2003 Publications

Deep chlorophyll maxima (DCM) represent high accumulations of algal biomass in the microaerobic metalimnion of mesotrophic lakes characterised by a few algal species which persist in time. We studied the accumulation of bacteria, protozoans and the mesozooplankton associated with the DCM of mesotrophic Grosser Vatersee in northern Germany over a three year period and related our findings to the pattern found in the epilimnion and the hypolimnion. More than 20% of the bacterial and protozoan biomass was concentrated in the narrow layer of the DCM, which comprised less than 10% of the whole water column. Between 16 and 36% of the rotifers and 12-31% of the juvenile cyclopoid copepods inhabited the DCM permanently on a day/night time scale, while calanoid copepods and adult cyclopoid copepods concentrated in the upper metalimnion and migrated into the DCM occasionally. Although bacteria and flagellates were generally larger in the DCM than in the epilimnion, ratios between bacterial and protozoan biomass were similar in both lake compartments. Our findings confirm a uniform community structure in the DCM of ciliates (Dexiotricha spp. and Strobilidium spp. comprised on average 70% of ciliate biomass) and, to a lesser extent, of mesozooplankton (rotifers and juvenile cyclopoid copepods dominated in the DCM). In contrast seasonal and interannual patterns of bacterial and protozoan biomass and cell size imply variation in the effects of predation.

We report that two structurally similar transposable elements containing reverse transcriptase (RT), Penelope in Drosophila virilis and Athena in bdelloid rotifers, have proliferated as copies containing introns. The ability of Penelope-like elements (PLEs) to retain introns, their separate phylogenetic placement and their peculiar structural features make them a novel class of eukaryotic retroelements.

The backwaters of the Delhi segment of the Yamuna River are shallow, weedy, and perennially open lentic habitats that harbor a rich variety of zooplankton, particularly rotifers. The present study is based on planktonic and epiphytic rotifers collected from these backwaters once a month over a period of 1 yr (September 1997 to August 1998). Planktonic rotifers were obtained by filtering water from the littoral zone through a plankton net, while epiphytic specimens were collected from the roots of Eichhornia crassipes and from floating and submerged leaves of Salvinia molesta. In total, 110 species belonging to 39 genera of 20 eurotatorian families were identified. Of these, five species of monogonont rotifers are new records from India, of which 2 are new to the Oriental region. The majority of the species were monogononts, while bdelloids were represented only by Rotaria sp. The largest fraction (76%) belonged to the following families: Lecanidae > Collurelidae > Brachionidae > Trichocercidae > Notommatidae > Flosculariidae. The fauna consisted mainly of cosmopolitan and tropicopolitan taxa except for 3 pantropical, 2 paleotropical, 2 arctic-temperate, 1 eastern hemispheric, and 1 holarctic taxa. The relative composition of planktonic and epiphytic rotifer species as well as the preference of the latter for the roots of Eichhornia compared to the leaves of Salvinia are discussed. Comments are also provided on species of special taxonomic and/or zoogeographic interest.

We examined the seasonal succession of the rotifer assemblages in the backwaters of the Delhi segment of the river Yamuna in relation to 18 physical-chemical variables across one year. These shallow, weedy, and perennial aquatic biotopes support a diverse and abundant zooplankton. A total of 89 rotifer species belonging to 34 genera and 18 families were recorded. Their seasonal dynamics were characterized by (i) maxima and minima in total densities during spring-early summer and winter, respectively; (ii) individual species reaching maximum and minimum densities during different seasons; and (iii) an absence of seasonal variation in species diversity. The relative importance of various physical and chemical factors in determining rotifer community structure and seasonal succession is evaluated and Pearson-product moment correlations between physical-chemical variates and rotifer densities are analyzed and discussed.

Tropical minute rotifer strains (SS-type) induce mixis at 30-35[degree]C but sexual reproduction and resting egg formation do not proceed well due to rapid environmental change. The present study examined the effect of temperature regulation on rotifer Brachionus rotundiformis (Langkawi strain, SS-type) resting egg formation in small (500 mL in culture volume)- and large-scale (500 L in culture volume) experiments. Rotifers were cultured at 30[degree]C in 15-17 p.p.t. seawater with an initial density of 1 individual (ind.)/mL. After 4 days, when cultures were in exponential growth stage with active mixis induction, the culture temperature of the experimental rotifers was changed to 25[degree]C. Control rotifers were cultured at 30[degree]C throughout the experiment. Fresh or frozen Nannochloropsis oculata and condensed freshwater Chlorella vulgaris were used as the rotifer diets in the small- and large-scale experiments, respectively. Significantly higher resting egg production was observed with the experimental rotifers (30[forward arrow]25[degree]C) versus the control rotifers. In the large-scale trial, experimental rotifers produced 2.6 x 106 resting eggs during a 9-day experiment, which was 1.6-fold more than the control rotifers. Moreover, the efficiency of resting egg formation was found to increase by a factor of 1.8. The present study indicates that decreasing culture temperature from 30 to 25[degree]C after active mixis increased resting egg formation in B. rotundiformis (SS-type).

Natural or anthropogenic movement of sediments may be an important vector for the dispersal of invertebrate resting stages between water bodies. Here we record the presence of invertebrate diapausing eggs in residual sediments from transoceanic vessels and explore whether these may pose an invasion risk. Viability of diapausing eggs was explored under light and dark conditions using sediment collected from eleven tanks on nine vessels operating on the Great Lakes. Seventeen cladoceran, copepod, and rotifer taxa were identified. Four of the species hatched have not yet been reported as established in the Great Lakes. Egg viability for individual species varied from 0% to 92%. Exposure to saline water may impact egg viability of some freshwater species. Generally, the proportion of eggs hatched in light and dark treatments did not differ significantly, indicating that light was not required to terminate diapause. As a result, eggs could potentially hatch in dark ballast tanks when immersed in freshwater loaded as ballast during operation on the Great Lakes. Viability of diapausing eggs differed among ballast tanks on a single vessel, indicating that tanks with independent ballast histories have different invasion risks. While additional work is needed to quantify risk, results from this study indicate that vessels entering the Great Lakes with only residual ballast are a potential vector for the introduction of new nonindigenous species during multiport operations.

The consequence of variable rates of clonal reproduction genetics of neutral markers are explored in diploid organisms within a subdivided population (island model). We use both analytical and stochastic simulation approaches. High rates of clonal reproduction will positively affect heterozygosity. As a consequence, nearby twice as many alleles per locus can be maintained and population differentiation estimated as F-ST value is strongly decreased in purely clonal populations as compared to purely sexual ones. With increasing clonal reproduction, effective populations size first slowly increases and then points toward extreme values when the reproductive system tends toward strict clonality. This reflects the fact that polymorphism is protected within individuals due to fixed heterozygosity. Contrarily, genotypic diversity smoothly decreases with increasing rates of clonal reproduction. Asexual populations thus maintain higher genetic diversity at each single locus but a lower number of different genotypes. Mixed clonal/sexual reproduction is nearly indistinguishable from strict sexual reproduction as long as the proportion of clonal reproduction is not strongly predominant for all quantities investigated, except for genotypic diversities (both at individual loci and over multiple loci).

The partial mitochondrial CO I gene was sequenced from 40 individuals of four Brachionus species. The sequences were compared and their molecular phylogenetic trees were constructed by UPGMA, neighbor-joining and maximum parsimony methods using B. plicatilis as outgroup. The length of sequences was 543 bp, in which frequency of A+ T was 65.3%, and a considerable variation of 157 nucleotide sites (28.9%) was detected. All of three trees suggested that B. quadridentatus is relatively closer to B. urceus than other species, and then to B. leydigi, last to B. calyciflorus. This result is consistent with that of traditional morphological taxonomy.

Sexual reproduction has long been proposed as a major factor explaining the existence of species and species diversity. Yet, the importance of sex for diversification remains obscure because of a lack of critical theory, difficulties of applying universal concepts of species and speciation, and above all the scarcity of empirical tests. Here, we use genealogical theory to compare the relative tendency of strictly sexual and asexual organisms to diversify into discrete genotypic and morphological clusters. We conclude that asexuals are expected to display discrete clusters similar to those found in sexual organisms. Whether sexuals or asexuals display stronger clustering depends on a number of factors, but in at least some scenarios asexuals should display a stronger pattern. Confounding factors aside, the only explanation we identify for stronger patterns of diversification in sexuals than asexuals is if the faster rates of adaptive change conferred by sexual reproduction promote greater clustering. Quantitative comparisons of diversification in related sexual and asexual taxa are needed to resolve this issue. The answer should shed light not only on the importance of the different stages leading to diversification, but also on the adaptive consequences of sex, still largely unexplored from a macroevolutionary perspective.

The meiofauna community (especially nematodes, oligochaetes and chironomids) in the streambed surface of two small submountain carbonate streams (Krahenbach and Korsch, Germany) was investigated from April 1998 to March 1999. The Krahenbach stream is relatively sorted and fine-grained, while the Korsch stream is more heterogeneous and coarse-grained. The streams also differ in velocity, water level, conductivity, chloride concentration and organic content of sediment. Total meiofauna density reached a maximum value of 906 individuals per 10(2) cm in the Krahenbach and 3166 individuals per 10(2) cm in the Korsch. Rotifers were the most abundant group in the Krahenbach (52% of total fauna), whereas nematodes were dominant in the Korsch (63%). Meiofauna showed one abundance peak in the Korsch and two abundance peaks in the Krahenbach. In the Krahenbach, distinct seasonal patterns at family and species level occurred, whereas in the Korsch even at high taxonomic level only one abundance peak was observed. The most abundant nematode family in both streams were Monhysteridae, followed by Tobrilidae in the Krahenbach and by Tylenchidae in the Korsch. The dominant oligochaete family in both streams were Naididae (especially Chaetogaster langi (Bretscher, 1896) and Nais elinguis (O. F. Muller, 1773)), followed by Tubificidae. The most abundant chironomid genera in the Krahenbach were Stichtochironomus and Corynoneura. Prodiamesa olivacea (Meigen, 1818) was the dominant chironomid species in the Korsch. Deposit-feeding and detritus-feeding animals were numerically dominant in both streams. The increased mean abundance of Diplogasteridae, Rhabditidae, Tubificidae and N. elinguis in the Korsch compared to that in the Krahenbach indicates an organically enriched situation.

The zooplanktonic fauna of Goksu dam lake was taxonomically investigated between April 1995 and December 1996. As a result, 16 species of cladocerans, three species of copepods and 28 species of rotifers, a total of 47 species, were identified in the lake. Of these, Monommata arndti (Rotifera) is a new record for Turkey's inland waters.

In recent years, most studies of the benthic microbial food web have either been descriptive or were restricted to the measurement of within sediment process rates. Little is known about benthic-pelagic coupling processes such as recruitment. We, therefore, developed an ex situ core incubation procedure to quantify the potential for microbial recruitment from the benthos to the pelagic in an acidic mining lake, Mining Lake 111 (ML 111; pH 2.6), in eastern Germany. Our data suggest that considerable zooplankton recruitment from the benthos takes place. Heliozoan and rhizopod recruitment in both summer and winter sediment cores was highest when they were incubated at 20 [degree]C. Maximum heliozoan recruitment was 23 ([plus or minus] 9 S.E.) individuals cm-2 day-1 (40% initial standing stock daily) in the winter 20 [degree]C incubation. Maximum rhizopod recruitment was 6 ([plus or minus] 2 S.E.) individuals cm-2 day-1 in the summer 20 [degree]C incubation. Little or no recruitment was apparent for either taxa when winter cores were incubated at 5 [degree]C, implying a temperature cue. Conversely, the rotifer, Cephalodella hoodi, exhibited a maximum recruitment of 6 ([plus or minus] 2 S.E.) individuals cm-2 day-1 during the winter 5 [degree]C incubation, representing 30% of initial standing stock daily, but little recruitment when incubated at 20 [degree]C. Cephalodella may have responded to an increased winter benthic food supply; in situ winter Chl a concentrations in the benthos were 3.4 times higher than those in the summer. The importance of this was reinforced by the poor pelagic food supply available in ML 111. In situ, Heliozoa, rhizopods and Cephalodella were first observed in the epilimnion of ML 111 in spring or early summer, suggesting active or passive recruitment following lateral transport from littoral sediments. Benthic-pelagic coupling via recruitment is potentially important in understanding the pelagic food web in ML 111 and warrants further investigation in this and other aquatic environments.

The first geographically extensive survey of rotifers in New England (U.S.A.) bogs is presented. Rotifers were collected during the summers of 1999 and 2000 from 31 bogs occurring throughout Vermont and Massachusetts, and in northwestern Connecticut. The survey incorporates three microhabitats within bogs: the bog ponds, interstitial (pore) water, and water-filled leaves of the northern pitcher-plant, Sarracenia purpurea L. Species similarity of these three habitats was low (Jaccard indices of similarity <0.25). During the survey over 50 000 individuals in 38 species were collected including Cephalodella anebodica Berzins and Colurella obtusa clausa (Hauer) which are reported for the first time from North America. Fifteen new species records for New England, 5 for Connecticut, 26 for Massachusetts and 20 for Vermont are also reported. Species richness of rotifers increased significantly with bog elevation but not with latitude, longitude, or bog area. The current known North American distribution of the rotifers we found in these bogs is presented for comparison.

Daily fluctuation of rotifer population abundance was studied in a lake and in a river of the Upper Parana River floodplain. Samples were collected in the open water for 14 consecutive days, in the high and low water periods. Densities were higher in the lake, chiefly in the low water period. During the studied period, changes in species dominance were observed. Rotifer abundance showed that higher variability occured during the high water period in both environments. Rotifer abundance showed high variability in the river during the sampling days. In the lake, fluctuation was related to the hydrological periods. Rotifer abundance fluctuations in the lake were influenced by regional factors (fluviometric level); and in the river, by local factors (flow). The sampling design pointed out that seasonal samples are necessary to evaluate rotifer abundance in the lake. However, this is not the case in the river where seasonal differences in abundance were not observed.

Two ESA facilities will be available for animal research and other biological experiments on the International Space Station: the European Modular Cultivation System (EMCS) in the US Lab Destiny and BIOLAB in the European Columbus Laboratory. Both facilities use standard Experiment Containers, mounted on two centrifuge rotors allowing either research in microgravity or acceleration studies with variable g-levels from 0.001 to 2.0xg. Standard interface plates provide each container with power and data lines, gas supply (controlled CO2, O-2 concentration and relative humidity), and -for EMCS only- connectors to fresh and waste water reservoirs. The experiment hardware inside the containers will be developed by the user, but ESA conducted a feasibility study for several kinds of Experiment Support Equipment with potential use for research on small animals: design concepts for experiments with insects, with aquatic organisms like rotifers and nematodes, and with small aquatic animals (sea urchin larvae, tadpoles, fish youngsters) are described in detail in this presentation. Also ESA's initial steps to support experiments with rodents on the Space Station are presented. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

During an ongoing study of the rotifer diversity in Thai peat swamps, several new or rare species were found. We here report on one new species, Lecane kunthuleensis n. sp., from a canal in Kun Thu Lee peat swamp, and on three rare species: Paracolurella aemula ( Myers, 1934) and Lecane junki Koste, 1975 from Kra Jood peat swamp ( Suratthanee province), and Lepadella punctataWulfert, 1939 from To- Daeng peat swamp ( Narathiwas province).

Inhabitants of a cryoconite hole formed in the Canada Glacier in the McMurdo Dry Valley region of Antarctica have been isolated and identified by small subunit (16S/18S) rDNA amplification, cloning, and sequencing. The sequences obtained revealed the presence of members of eight bacterial lineages (Acidobacterium, Actinobacteria, Cyanobacteria, Cytophagales, Gemmimonas, Planctomycetes, Proteobacteria, and Verrucomicrobia) and metazoan (nematode, tardigrade, and rotifer), truffle (Choiromyces), ciliate (Spathidium), and green algal (Pleurastrium) Eukarya. Bacterial recovery was similar to20-fold higher at 4 degreesC and 15 degreesC than at 22 degreesC, and obligately psychrophilic bacteria were identified and isolated. Several of the rDNA molecules amplified from isolates and directly from cryoconite DNA preparations had sequences similar to rDNA molecules of species present in adjacent lake ice and microbial mat environments. This cryoconite hole community was therefore most likely seeded by particulates from these local environments. Cryoconite holes may serve as biological refuges that, on glacial melting, can repopulate the local environments.

Abundance and body size of zooplanktonic organisms, testate amoebae, rotifers, cladocerans and copepods from the littoral and pelagic regions of three lakes were analyzed in February and August 2000. The lakes belong to three different river systems (Baia, Ivinhema and Parana rivers) of the upper River Parana floodplain. It was expected that average body size was different in space ( regions of the lake and limnological characteristics) and time ( summer and winter) because the variation of depth, pH, oxygen dissolved, chlorophyll-a and water temperature of each lake. Zooplankton community was represented by 119 species. Sorensen's coefficient showed that the three communities were similar. Larger organisms were found in the lakes' pelagic region, and seasonally larger individuals were registered in the winter and smaller individuals in the summer. The relationship between body size and density was slight, positively significant. The body size frequency distribution was bi-modal. ANOVA results showed a significant influence of the interaction of the littoral and pelagic regions, lakes, and seasons in the body size of zooplankton organisms. Spatial and temporal changes of the community size structure of zooplanktonic assemblages were related to the food resource (microbial-loop or herbivore chain), species habitat preference and life strategies ( growth and reproduction).

We tested the effects of UV-B stressed algae on grazing rates of zooplankton. Four algal species (Chlamydomonas reinhardtii, Cryptomonas sp., Scenedesmus obliquus and Microcystis aeruginosa) were used as food and fed to three zooplankton species (Daphnia galeata, Bosmina longirostris and Brachionus calyciflorus), representing different taxonomic groups. The phytoplankton species were cultured under PAR conditions, and under PAR supplemented with UV-B radiation at two intensities (0.3 W m-2 and 0.7 W m-2, 6 hours per day). Ingestion and incorporation experiments were performed at two food levels (0.1 and 1.0 mg C l-1) using radiotracer techniques. The effect of food concentration on ingestion and incorporation rate was significant for all three zooplankton species, but the effect of UV-B radiation was more complex. The reactions of the zooplankton species to UV-B stressed algae were different. UV-B stressed algae did not affect Daphnia grazing rates. For Bosmina the rates increased when feeding on UV-B stressed Microcystis and decreased when feeding on UV-B stressed Chlamydomonas, compared with non-stressed algae. Brachionus grazing rates were increased when feeding on UV-B stressed Cryptomonas and UV-B stressed Scenedesmus, and decreased when feeding on UV-B stressed Microcystis, compared with non-stressed algae. These results suggest that on a short time scale UV-B radiation may result in increased grazing rates of zooplankton, but also in decreased grazing rates. Long term effects of UV-B radiation on phytoplankton and zooplankton communities are therefore difficult to predict.

Pourriotia carcharodonta gen. et sp. nov. is described from freshwater plankton collected at the subantarctic Kerguelen islands. The new taxon is provisionally placed in the Notommatidae. Main diagnostic characters separating the new taxon and the other genera of the family are provided by the morphology of the trophi. Apical rami chambers with toothed inner margin and blunt projection on outer margin. Apical rami teeth and subuncinal teeth with accessory spines. Proximal margin of major uncinal teeth firmly connected to distal margin of apical chambers, forming grasping unit. Fulcrum dumb-bell-shaped. Information is presented on the trophi structure of the genus Pleurata (Notommatidae).

A new dicranophorid rotifer, Paradicranophorus sinus sp. nov., is described from periphyton originating from poikilohaline waters in Belgium. The main distinguishing taxonomic features of the new species are intramallei with supramanubria and a pair of preuncinal teeth. Taxonomic problems associated with the genus Paradicranophorus are briefly discussed. A new genus, Donneria, is proposed to accommodate Paradicranophorus sudzukii Donner, 1968. Information is presented on the trophi of P hudsoni (Glascott, 1893) and D. sudzukii (Donner, 1968). Encentrum brevifulcrum Dartnall, 1997 is synonymised with P sordidus Donner, 1968.

Evolutionary relationships within the phylum Rotifera are poorly understood despite the important role that they play in freshwater ecosystems. Phylogenetic analyses of DNA sequences from two mitochondrial genes, 16S rDNA and cytochrome oxidase I (COI), were employed to examine the extent of genetic divergence within populations of several common taxa. This work sought to verify the role of phenotypic plasticity versus genetic variation in explaining the morphological variation in some taxa. Deep genetic divergence (4.4% COI nucleotide sequence divergence) was detected between spined and unspined forms of Keratella cochlearis, which suggests that they represent different species. However, morphological variation in K. hiemalis appeared to be environmentally induced. The study also sought to ascertain the role of one environmental variable, salinity, in the patterning of sequence variation. Greater haplotype diversity and genetic divergence were observed among populations of halophilic Brachionus plicatilis than among freshwater Keratella quadrata populations from northern Canada. When COI DNA sequences for B. plicatilis haplotypes were compared with those from Spain, there was evidence for considerable genetic diversity within this species among closely located saline lakes in northern Canada.

Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO4 and CO3, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5 - 3 gl(-1) total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (lambda(1) = 0.97 and lambda(2) = 0.62, P < 0.05). The rotifer Brachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO4/CO3-dominated lake water with elevated potassium (79 - 128 mg l(-1)) and total phosphorus concentrations (1322- 2915 &mu;g l(-1)). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO4/CO3 are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.

1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35,901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton (Stephanodiscus, Cyclotella-like, large diatoms, Skeletonema and non-siliceous algae) to model filter-feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus-like and Keratella-like rotifers. 2. According to density estimates from field surveys (Bachmann V. et al. (1995) Hydroecologie Appliquee, 7, 185, Bachmann V. & Usseglio-Polatera P. (1999) Hydrobiologia, 410, 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers. 3. The simulations suggest a significant impact of benthic filter-feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton. 4. A daily carbon balance for a typical summer shows the effect of benthic filter-feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches.

Diel vertical migration (DVM) behaviour is a predator avoidance mechanism observed within many zooplankton species in the presence of zooplanktivorous fish. A 24-h survey was carried out in June 1998 to investigate diel variation in the vertical distribution of fish, zooplankton and phytoplankton (chlorophyll) in Lake Kinneret, Israel. Fish revealed diel variation in vertical distribution but had no spatial overlap with zooplankton, and consequently no apparent influence on zooplankton dispersal. Zooplankton revealed some diel variation in distribution being affected by thermocline and oxycline position and movement of the internal the internal seiche wave. Cyclopoid species closely follow the movement of the seiche wave implying that, due to their greater motility, they are following conditions that are suitable to them. The Cladocera species and small rotifers only partly, which may be part of their phototaxic behaviour. Physical forces like convection, horizontal and vertical forcing probably have a role in contributing to a homogeneous distribution of the plankton by preventing stratification or interfering with the more motile zooplankton which may be attempting to migrate.

Rotifer communities inhabiting wet sands of lake beaches are dependent in their functioning on permanent input of organic matter from neighbouring sites. The aim of the study is to test the hypothesis that trophic state of lake waters may influence densities and structure of psammon communities of Rotifera. Studies were carried out in hydro-, hygro- and euarenal of 44 beaches in 18 lakes of different trophy in summer 1999 (since 2 till 17 July) and 38 beaches in 16 lakes in spring 2000 (since 10 till 23 May). Psammon was sampled always between 10 a.m. and 2 p.m. at similar weather conditions (no shadow. rains and strong winds). Interstitial waters were mostly alkaline and contained less oxygen than lake ones and oxygen concentrations decreased upward water line. Very high variability of phosphate P content made differences between trophic groups of lakes not significant. Similarly, concentrations of P total were more or less similar in all studied trophic groups of lakes. Total nitrogen values were increasing from meso-eutrophic to hypertrophic lakes in spring, whereas this trend was not observed in summer. Chlorophyll a concentrations were similar in meso-, meso-eu- and eutrophic and markedly higher in hypertrophic lakes. In general, some tendency to increasing values of chemical parameters with increasing trophy may be seen if their ranking list is compared. Rotifers were present in all studied stations. In total, 110 species (i.e. ca. 26% of all records of rotifer species in Poland) were found with 22 species occurring exclusively in psammon. Three species new in rotifer fauna of Poland were discovered [long dash] Cephalodella psammophila, Collotheca wiszniewski and Euchlanis dapidula. Generally all trophic groups of lakes were relatively similar as regards species structure of rotifer communities with rotifers of the genus Lecane playing most important role. The index of Percentage Similarity of Community calculated for randomly chosen 30 pairs of particular beaches from the same lake and for beaches of different lakes was in both cases almost identical. Species of high frequency constituted the overwhelming majority of individuals forming rotifer communities of all beaches. Taxons met in 1 to 5 lakes decided on faunistic originality of the communities. Some tendency was observed for higher diversity of psammon rotifer communities in mesotrophic and eutrophic lakes. The lowest values of diversity index occurred mostly in hypertrophic lakes. Psammobionts constituted only 20% and psammoxens 10% of the community abundance in all lakes and all zones of the beaches, whereas psammophilic rotifers decidedly dominated (70%). Rotifer abundance was relatively similar in eu- and hypertrophic lakes and markedly higher in mesotrophic and lower in meso-eutrophic lakes. However, due to high fluctuations of the values noted in particular beaches the differences were not significant in any of the possible configurations of compared data. Monogononta played much more important role in rotifer densities than bdelloids. The hypothesis on advantageous influence of high trophy of lake waters on abundance of psammon communities of Rotifera cannot be supported by results of this work. In lakes of moderate trophy (from meso- to eutrophy) the amount of nutrients and chlorophyll does not seem to influence psammon communities. In hypertrophic lakes this impact is observed, but it seems to be rather unfavourable for psammon rotifers. The communities in hypertrophic lakes are poorer in species, less diversified and less original. The group of animals developing well in this group of lakes are bdelloids. Species composition nad community structure of psammon rotifers seem to be rather determined by many different factors, lake trophy being only one of them and probably not the main one.

Is inshore, 2-cm layer of wet sand an ecotone? An attempt of this study is to answer the question by analysing characteristic patterns of a structure of rotifer communities inhabiting the psammolitoral zone. Psammon was sampled from sandy shore of a mesotrophic Lake Kuc (Masurian Lakeland, Poland), weekly from May to November 1996 and on one occasion in May 1998. Despite of extremely unfavourable conditions of their abiotic habitat, psammon rotifers of Lake Kuc were reaching occasionally extremely high densities. Seasonal dynamics of numbers and structure of psammon rotifer communities reflected variable character of their habitat. A course of the changes was similar in less variable higropsammon and extremely variable eupsammon. Patterns formed in psammolittoral [long dash] when illustrated with qualitative and quantitative features of psammon rotifer communities [long dash] fit definitions of an ecosystem, an ecotone, a part of a land /water ecotone, a microlayer in the ecosystem or a specific boundary zone in the lake ecosystem.

A prominent feature of Lake Nasser is the presence of khors (dendritic side extensions). We studied the zooplankton of the larger khors and coastal zone of the main lake in 1996 and 1997, and found an assemblage of rotifers, cladocerans and copepods that was partly tropical, partly temperate, at relatively high biomasses. Spatial differences were weak, but the upstream khors (Toushka and Korosko) were consistently richer than the downstream khors (El-Ramla and Kalabsha), with a rather sudden transition around km 150 at El Madiq. Summer standing crops were higher than those in winter by a factor 2-3. The zooplankton of the littoral of the main channel showed the same spatial pattern as that in the khors, being more abundant in spring (average 82 300 ind m-3) than in autumn (average 72 700 ind m-3). Zooplankton dry weight increased from 4 g m-2 at khor El-Ramla to 7 g m-2 at khor Toushka. These rather high values had low variation. The number of species, diversity and evenness all showed a high degree of similarity among the khors and in the littoral of the main lake. The lake fish fauna is poor, lacking a pelagic planktivore. The predominance of medium-sized Copepoda (one calanoid, two cyclopoids) in the zooplankton suggests that fish predation is moderate. This is confirmed by the persistence of two Daphnia species at low abundance, although rather strong variations in time suggest that Cladocera suffer from summer predation by invertebrates (copepods) as well as vertebrates (mostly larval fish). Because the zooplankton is underutilised by higher trophic levels, we suggest to assess the benefits of introducing a pelagic zooplanktivorous fish.

The vertical distribution of herbivorous zooplankton was examined over a 24-hr period in Lake Somerville, Texas, a shallow, well-mixed, warm-water reservoir in which temperature and oxygen gradients rarely occur. While no consistent preference for surface or bottom water was found, diel zooplankton population deficits were observed. Activity of the main planktivore, the non-visual, filter feeding gizzard shad, did not correspond to observed trends for zooplankton. Other factors such as sinking and resuspension of phytoplankton might have been important.

In the present work we tested the effect of Chlorella vulgaris and Scenedesmus acutus in different proportions on the population growth of Brachionus calyciflorus, Brachionus patulus, Ceriodaphnia dubia, and Moina macrocopa. In general, both rotifer species grew well on either type of algae. Regardless of algal mixture, B. calyciflorus had a shorter initial phase, while B. patulus needed more than a week to begin the exponential phase of growth. Both the rotifer species showed consistently better population growth with Chlorella than on Scenedesmus, or the mixture. At any given algal combination, B. patulus had higher peak values than B. calyciflorus. The rate of population increase (r) for both the rotifers varied from 0.18 to 0.48 d(-1) depending on the algal type and combination. Regardless of algal type and combination, B. calyciflorus had a much higher value of r than B. patulus. Both C. dubia and M. macrocopa grew on the algal types, whether offered separately or in mixture. Regardless of the treatment type, C. dubia needed a longer period (about 2 weeks) than M. macrocopa to reach peak abundances. Thus, our study did not support the view that Scenedesmus is consistently superior to Chlorella as a basic diet to the tested species of zooplankton.

Floscularia ringens is a cosmopolitan, sessile rotifer (class Monogononta) that lives inside a tube it constructs from numerous small, rounded pellets. Adults of F. ringens produce parthenogenetic eggs that are retained within the tube. Upon hatching, juveniles remain within the maternal tube for a short time completing their development before swimming away. The free-swimming juvenile has a conical body, short foot, small corona, and mastax with trophi, but appears unable to feed. After a short time (<1 day), the young rotifer attaches permanently to a substrate and its morphology changes radically: the corona develops 4 wide lobes and the foot elongates, becoming slender and retractable. Once the corona has developed, the young animal begins to feed by producing filtering currents, and also starts to build its own tube. Here we report 4 new morphological details regarding this species. (1) A specialized epidermal groove is present on the trunk in front of the cloaca. (2) A small hole is located in the center of the inner surface of each pellet of the tube. (3) The muscles inside the foot are U-shaped in transverse section. (4) The size of the trophi remains unchanged during growth of the juvenile into an adult.

Faunistic data concerning rotifer species not previously cited for the Italian fauna are reported. They are all found in the northwestern part of the country and belong to 24 genera, seven of which are new for Italy: Cyrtonia, Didymodactylos, Eosphora, Mikrocodides, Pleuretra, Proalinopsis, and Taphrocampa. For some of these species, data on rearing in laboratory cultures, dimensions, and SEM pictures of trophi or whole animals are given.

Pleuretra hystrix Bartos, 1950 is a peculiar bdelloid rotifer unrecorded for more than 50 years since its description. We found this species in the western Italian Alps and we redescribe it, confirming the validity of this species. New morphological details are described from scanning electron micrographs. Variability in spines on the trunk is great; their adaptative significance in bdelloid rotifers is discussed.

We describe some rare epizoic rotifers found on Potamon fluviatile (Herbst, 1785) from Italy. Three species are discussed: Lecane branchicola (Piovanelli, 1903) (Monogononta, Lecanidae; new synonym: L. piovanellii Bartos, 1957), Anomopus telphusae Piovanelli, 1903 and Embata parasitica (Giglioli, 1863) (Bdelloidea: Philodinidae). Lecane branchicola, previously considered a nomen nudum after Bartos (1957), is redescribed, and its identity is stabilized by the designation of a neotype. Both L. branchicola and A. telphusae are particularly rare, and have been found on a few occasions only. Lecane branchicola appears to be restricted to a specific body part of their host, namely the branchial chamber. On the contrary, E. parasitica has been recorded as epizoic from several hosts and regions. SEM photographs of the trophi of the three species are presented.

The effects of the pyrethroid insecticide cypermethrin on a natural freshwater community were studied in small in situ enclosures over an 11-day period. The experiment was conducted in a eutrophic lake using a regression design that included three untreated controls and a gradient of six unreplicated cypermethrin concentrations, ranging from 0.01 to 6.1 mu g/l. This paper is the first in a series of two, and describes the fate of cypermethrin and its effects on the abundance of crustaceans, rotifers, protozoans (cilliates and heterotrophic nanoflagellates (HNF)) and bacteria and the biomass of periphytic and planktonic algae. The concentration of cypermethrin decreased quickly during the experiment, with a half-life of 48 h for the total and 25 h for the dissolved fractions of cypermethrin, respectively. Cypermethrin proved to be acutely toxic to crustaceans in enclosures receiving nominal cypermethrin concentrations of 0.13 mu g/l. No Effect Concentration (NEC) and median Effect Concentration (EC50) for the total crustacean community and cladoceran and copepod subgroups ranged between 0.02-0.07 and 0.04-0.17 mu g/l, respectively, with copepods being less sensitive than cladocerans. The abundance of rotifers, protozoans and bacteria and the chlorophyll-a concentration of planktonic and periphytic algae was significantly related to the concentration of cypermethrin. All groups proliferated within 2-7 days after the cypermethrin application in those enclosures where the abundance of crustaceans was seriously affected by cypermethrin (i.e. 0.13 mu g/l). We hypothesise that the proliferation of rotifers, protozoans, bacteria and algae was due to a reduced grazer control from crustaceans and thereby mediated indirectly by cypermethrin. The results of this experiment provide knowledge on how an entire microplankton community may respond to pyrethroids in nature, and the indirect effects observed on the community clearly demonstrates the necessity of multispecies field experiments in ecotoxicological risk assessment.

Microevolution is typically ignored as a factor directly affecting ongoing population dynamics. We show here that density-dependent natural selection has a direct and measurable effect on a planktonic predator-prey interaction. We kept populations of Brachionus calyciflorus, a monogonont rotifer that exhibits cyclical parthenogenesis, in continuous flow-through cultures (chemostats) for more than 900 days. Initially, females frequently produced male offspring, especially at high population densities. We observed rapid evolution, however, towards low propensity to reproduce sexually, and by 750 days, reproduction had become entirely asexual. There was strong selection favouring asexual reproduction because, under the turbulent chemostat regime, males were unable to mate with females, produced no offspring, and so had zero fitness. In replicated chemostat experiments we found that this evolutionary process directly influenced the population dynamics. We observed very specific but reproducible plankton dynamics which are explained well by a mathematical model that explicitly includes evolution. This model accounts for both asexual and sexual reproduction and treats the propensity to reproduce sexually as a quantitative trait under selection. We suggest that a similar amalgam of ecological and evolutionary mechanisms may drive the dynamics of rapidly reproducing organisms in the wild.

Microevolution is typically ignored as a factor directly affecting ongoing population dynamics. We show here that density-dependent natural selection has a direct and measurable effect on a planktonic predator-prey interaction. We kept populations of Brachionus calyciflorus, a monogonont rotifer that exhibits cyclical parthenogenesis, in continuous flow-through cultures (chemostats) for more than 900 days. Initially, females frequently produced male offspring, especially at high population densities. We observed rapid evolution, however, towards low propensity to reproduce sexually, and by 750 days, reproduction had become entirely asexual. There was strong selection favouring asexual reproduction because, under the turbulent chemostat regime, males were unable to mate with females, produced no offspring, and so had zero fitness. In replicated chemostat experiments we found that this evolutionary process directly influenced the population dynamics. We observed very specific but reproducible plankton dynamics which are explained well by a mathematical model that explicitly includes evolution. This model accounts for both asexual and sexual reproduction and treats the propensity to reproduce sexually as a quantitative trait under selection. We suggest that a similar amalgam of ecological and evolutionary mechanisms may drive the dynamics of rapidly reproducing organisms in the wild.

Ancient asexuals have been considered to be a contradiction of the basic tenets of evolutionary theory. Barred from rearranging genetic variation by recombination, their reduced number of gene arrangements is thought to hamper their response to changing environments. For the same reason, it should be difficult for them to avoid the build-up of deleterious mutations. Several groups of taxonomically diverse organisms are thought to be ancient asexuals, although clear evidence for or against the existence of recombination events is scarce. Several methods have recently been developed for predicting recombination events by analyzing aligned sequences of a given region of DNA that all originate from one species. The methods are based on phylogenetic, substitution, and compatibility analyses. Here we present the results of analyses of sequence data from different loci studied in several groups of evolutionarily distant species that are considered to be ancient asexuals, using seven different types of analysis. The groups of organisms were the arbuscular mycorrhizal fungi (Glomales), Darwinula stevensoni (Darwinuloidea crustacean ostracods) and the bdelloid rotifers (Bdelloidea), which are thought to have been asexual for the last 400, 25-100, and 35-40 Myr, respectively. The seven different analytical methods evaluated the evolutionary relationships among haplotypes, and these methods had previously been shown to be reliable for predicting the occurrence of recombination events. Despite the different degree of genetic variation among the different groups of organisms, at least some evidence for recombination was found in all species groups. In particular, predictions of recombination events in the arbuscular mycorrhizal fungi were frequent. Predictions of recombination were also found for sequence data that have previously been used to infer the absence of recombination in bdelloid rotifers. Although our results have to be taken with some caution because they could signal very ancient recombination events or possibly other genetic variation of nonrecombinant origin, they suggest that some cryptic recombination events may exist in these organisms.

Littoral rotifers and cladocerans feed on bacteria, phytoplankton, and detritus. In comparison to planktonic organisms their species diversity is high, yet little is known about their biology. In this study we present data on the functional response of the cladocerans Macrothrix triserialis and Alona rectangula, and the rotifer Brachionus macracanthus to different levels of the alga Chlorella vulgaris. Based on the incipient limiting level, we chose the food concentration and tested the population growth on four types of diets for three cladoceran species - Macrothrix triserialis, Alona rectangula, and Chydorus sphaericus - and three rotifer species - Brachionus macracanthus, Lecane quadridentata, and Platyias quadricornis. We studied growth rates of each of these species on diets of live Chlorella vulgaris, heat-killed Chlorella vulgaris, baker's yeast (Saccharomyces cerevisiae), and field collected detritus. The incipient limiting level was around 0.9 . 10(6) cells mL(-1) of Chlorella for the tested zooplankton species. The population growth patterns showed that, in general, the cladocerans took 25 . . . 50 d to reach their peak population densities, which ranged from 10 . . . 75 ind. mL(-1). Among the rotifers L. quadridentata and B. macracanthus had equally high growth rates on live and heat-killed forms of C. vulgaris while P quadricornis grew best on detritus. The growth rates ranged from 0.03...0.21 d(-1). The similarities and differences between littoral and planktonic organisms in relation to food type and availability have been discussed.

The effects of food component and concentration on the population growth, body size, and egg size of freshwater rotifer Brachionus rubens were studied using population accumulative culture method. The results showed that there were very significant effects of food component and concentration on the population growth rate, body volume and egg volume. Among three types of algal food, the population growth rate of rotifers fed with Chlorella pyrenoidosa was lowest, and that fed with Scenedesmus obliquus was the highest. Rotifers fed with C. pyrenoidosa had the smallest body volume, but there were no significant difference between the two others. The relationship between population growth rate and food concentrations was curvilinear, and it could be described as Y=-0.0040 X2+0.0409 X+0.4471. The body and egg volumes tended to be smaller, when the food concentrations were higher than 6.0x106 cells[center dot]ml-1 and or lower than 3.0x106 cells[center dot]ml-1.

Plankton populations and physico-chemical parameters were evaluated monthly over a year period in the springs Ain El-Sera and El-lmam El-Shaffie. The objective of the work presented here was to characterize the water quality and the seasonal succession of phytoplankton and zooplankton in these ecosystems. The influence of seasonal factors on the zooplankton translated into alternating populations dominated by rotifers (Brachionus) in autumn and winter, and by Cladocera specially Daphnia in winter in case of Ain El-Sera ecosystem. In El-Imam EI-Shaffie ecosystem the zooplankton community was dominated by the cladoceran Artemia in spring which is reddish in colour and gives the water a rosy tint. Of the phytoplankton in Ain El-Sera spring were Oocystis solitaria and Closterium pronum (Chlorophyceae), the predominant taxonomic units in spring whilst Peridinium (Dinophyceae), dominated during the months with lowest irradiance (autumn). In El-Imam EI-Shaffie spring, Closterium pronum dominated in summer but Nitzschia linearis was abundant in winter followed by the cryptophycean Clamydomonas. Physico-chemical properties of these springs indicated their therapeutic importance. The water temperature of the two springs varied from 18[degree]C to 24[degree]C. The two springs are of alkali type. pH varied from 7.6 to 8.3 . Conductance and salinity in El-Imam EI-Shaffie spring were ten-folds those of Ain El-Sera spring. Dissolved oxygen varied from 7.0mg/L in spring in El-Imam EI-Shaffie spring water to 8.7mg/L in Ain El-Sera spring water . The concentrations of Ca, Mg and S04 were very high in the two springs Recommendations for the protection of these thermal springs are given according to the results of this study.

Crowding induced the production of mictic (male-producing) females in Brachionus calyciflorus from two North American strains and an Australian strain. The specificity of this response to crowding was tested by culturing single individuals of a North American clone in three treatment conditions: a small volume (high density), a large volume (low density), and a large volume with a high density of an Australian clone. The results were consistent and clear in six experiments using different combinations of clones. Crowding low-density individuals of the North American strains with the Australian strain failed to induce them to produce mictic females. The mictic-female response in this treatment was similar to that in the low-density treatment, and both of these responses were significantly lower than that in the high-density treatment. Since the mictic-female response to crowding in Brachionus is mediated by a chemical produced by the rotifers themselves, the chemical inducers produced by the Australian and North American strains must be different. Taxonomically specific responses to crowding should increase fitness by assuring that sexual reproduction in the heterogonic life cycle coincides with a high population density of individuals able to mate with one another and, thus, when the production of fertilized resting eggs can be maximized. This would be especially important in plankton communities with diverse rotifer assemblages and multiple congeneric species. Otherwise, a low-density population of a species could be induced to initiate bisexual reproduction by populations of other species, curtailing its potential for population growth via female parthenogenesis and limiting its production of resting eggs in the future.

A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis. Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs.Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta, and rarely or never settled on the rotifer Keratella, the cladocerans Bosmina and Scapholeberis, and the body of the copepod.Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 degree C. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate ( lambda =26 day super(-1)); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare. 4. Life-table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.

Induction of mictic females, and hence initiation of sexuality, in the life cycle of some Brachionus requires an environmental stimulus associated with crowding. The inducing stimulus appears to be a taxonomically specific chemical released into the environment by the rotifers. Oocytes are induced to develop into mictic females before they are oviposited by their amictic mothers and begin cleavage divisions. Thus, the inducer affects the oocyte in the maternal body cavity either directly or indirectly by altering the physiology of its mother. The level of sexual reproduction expressed in populations of a Florida strain of B. calyciflorus is controlled by two types of endogenous factors and by the degree of crowding. First, some fraction of genetically identical oocytes in a clonal population fails to respond to even extreme crowding conditions, thus ensuring some potential for continued population growth by female parthenogenesis. Second, the propensity of amictic females to produce mictic daughters is extremely low when they hatch from fertilized resting eggs and then gradually increases to an asymptote after about 12 parthenogenetic generations. This multigenerational parental effect likely is due to a cytoplasmic factor in fertilized eggs that inhibits expression of the mictic-female phenotype and that is gradually diluted in successive parthenogenetic generations. The effect may increase a clone's genetic contribution to the resting-egg bank by increasing its population size through parthenogenetic generations before mictic females are induced.

1. A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis . Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs.2. Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta , and rarely or never settled on the rotifer Keratella , the cladocerans Bosmina and Scapholeberis , and the body of the copepod.3. Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 degreesC. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate (lambda=4.26 day(-1)); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare.4. Life-table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.

The taxonomic composition, abundance and biomass of microzooplankton were studied at eight stations in Lake Shinji–Ohashi River–Lake Nakaumi brackish-water system, Japan, monthly from April 1998 to March 1999. Over the entire area, naked ciliates numerically dominated the microzooplankton community (annual mean 39.6%) followed, in order, by tintinnids (30.3%), copepod nauplii (24.6%) and rotifers (5.5%). The abundance of each taxonomic group of microzooplankton varied geographically due to large salinity variations (range 1.5–33.3 p.s.u.). It was notable that naked ciliates occurred overwhelmingly in Lake Shinji (54.9% of total microzooplankton) and rotifers were relatively numerous in Lake Shinji (8.8%) and Ohashi River (11.1%), where the salinity was lower (annual mean 4.1 and 13.6 p.s.u., respectively) than in Lake Nakaumi and Sakai Strait (26.3 and 29.8 p.s.u., respectively). Owing to large seasonal temperature variation (range 5.4–29.8[degree]C), the abundance of microzooplankton showed marked seasonal variations, being higher in spring and summer than in the remaining seasons. A total of 49 species of tintinnids were identified, and 15 of these species reached concentrations >500 individuals l-l. The occurrence of most tintinnid species was confined to certain months or locations, closely associated with species-specific temperature and salinity preference and/or tolerance. In this eutrophic system, food supply for microzooplankton might be sufficient due to extremely high chlorophyll a concentration (annual mean 8.8 [mu]g l-l in Sakai Strait to 22.6 [mu]g l-l in Lake Shinji). However, microzooplankton biomass remained moderate (range 0.19–18.7 [mu]g C l-l) due probably to heavy predation by mesozooplankton, which inhabit this brackish-water system at extremely high biomass.

Five Gram-negative bacterial strains, oxidase-positive, motile by means of more than one polar flagella, facultative anaerobe, arginine dihydrolase-negative, lysine- and ornithine decarboxylase-positive, sensitive to the vibriostatic agent O/129, were isolated from a flow-through rotifer culture system in Gent, Belgium, and previously characterized by fluorescent amplified fragment length polymorphism. Comparison of the 16S rDNA sequence of strain LMG 21460T indicated close relationships ([approximately]99% similarity) to Vibrio campbellii, Vibrio harveyi, Vibrio alginolyticus and Vibrio parahaemolyticus. However, DNA hybridization experiments revealed similarity values below 70% with its closest species V. campbellii and V. harveyi. Additionally, the analysed strains differ from related Vibrio species by the utilization of melibiose and production of acid from L-arabinose and amygdalin. Among the strains analysed, differences were observed in some phenotypic characters, particularly susceptibility to ampicillin, polymyxin B and amikacin, and urease activity. The major fatty acids identified were 16:0, 18:1[omega]7c, 14:0, 12:0 3-OH and 18:0. Vibrio rotiferianus sp. nov. is proposed, with type strain LMG 21460T (=CAIM 577T); it has a DNA G+C content of 44.5[plus or minus]0.01 mol%.

Zooplankton from Lake Coatetelco, a shallow tropical reservoir in Morelos State, Mexico, was surveyed monthly through one year. The entire zooplankton community was represented by only five species, with the calanoid Arctodiaptomus dorsalis overwhelmingly dominant throughout the year. A cyclopoid copepod species, one cladoceran species, and two species of rotifers completed the zooplankton. Although some seasonal fluctuations were noted, zooplankton abundance did not appear related to simple physiocochemical parameters; however, there was a general inverse relationship between zooplankton and phytoplankton.

Aquatic organisms, ranging from bacteria to fish, living in clear lakes are presently receiving damaging levels of UV radiation. Photoreactivation is a light-dependent mechanism by which some organisms deal with DNA damage caused by UV radiation. Yet, photoreactivation is a mechanism that confounds long-term predictive modeling of UV effects on the survival of these organisms. Here we show that a short-lived rotifer species, Asplanchna girodi, previously thought to have little to no photoreactivation, does indeed have a significant amount of it. The ability to undergo photoreactivation in A. girodi is dependent on age and becomes apparent only after several days of observation after UV exposure.

The Okavango Delta has an annual flood cycle that spreads slowly from the northwestern 'panhandle' into a widening delta to the southeast. Rotifers were sampled from areas where the flood was active, and from other areas not yet reached by the flood. In still waters, the samples were dominated by euplanktonic rotifers, particularly of the genera Brachionus, Keratella and Hexarthra, with about 20 species per 1000 individuals at a station. Where the water was moving the samples were dominated by periphytic rotifers, with over 100 species per 1000 individuals at a single station. The periphytic species were dominated by the genus Lecane, with over 45 species, followed by Lepadella with 24 species, and Trichocerca with 23 species. Comparison of the Okavango with six other tropical localities reveals fairly consistent ratios of the numbers of species in the periphytic genera Lecane, Lepadella and Trichocerca, indicating that there may be assembly rules for communities of tropical periphytic rotifers.

Trophic-niche differentiation is often cited as a main factor in structuring zooplankton assemblages, although field evidence for this is rarely presented. The study was based on a survey of 29 Pyrenean lakes with altitudes ranging between 1,875 and 2,990 m carried out during July and August 2000. Because of the oligotrophic nature of these lakes, we aimed to confirm that food partitioning is a major factor in shaping zooplankton assemblages. We analysed the amino acid composition of six cladocera and seven copepod species. A discriminant analysis showed that each species could be distinguished according to its amino acid composition. A negative relationship between amino acid differentiation and co-occurrence among the cladocera and cyclopoid copepod was observed. In contrast, calanoids did not show any relationship and were characterised by a high amino acid differentiation between species. As the differences in the amino acid composition among zooplankton species indicate distinct food sources, the relationship found indicates that trophic-niche differentiation plays a key role in determining the assemblage of these zooplankton communities. Therefore exploitative competition, either at present or in the past by driving co-evolutionary histories, has been a significant factor in structuring the cladocera and cyclopoid communities in these oligotrophic lakes.

In recent decades, net-cage aquaculture has become one of the main patterns of the intensive fish-culture in the lakes, reservoirs and even rivers in China. This aquaculture pattern results in enriching exogenous nutrients in water and, consequently, accelerates the process of lake eutrophication. To ensure that normal environmental conditions and fisheries in a lake remain sustainable, qualitative estimations of nutrients in relation to ecosystem changes are essential. A study, mainly on nitrogen (N) and phosphorus (P) influences due to cage fish-culture was carried out in a shallow 35.5 ha bay in Niushanhu Lake, a shallow lake located in middle Yangtze Basin, during the period from March to December 2000. Net-cages in total covered an area of 1000 m(2) and the annual fish yield was 16.0 metric tons (MT). Fish feeding residue entering the water during the period was equivalent to 1532.9 kg of total N and 339.2 kg of total P. Sampling and analyses of the total N and total P concentrations, diversity and biomass of plankton and Chi a were made monthly, while data on zoobenthos were collected twice, respectively, at the beginning and the end of the study. Results showed that the Chi a content in water was correlated negatively to distance from the cage. The Chi a content that is converted into wet biomass of phytoplankton may be expressed by the regression: B = 2.673 - 0.0016D (B, biomass in mg/l; D, distance in km, r=0.9362; n=7). The biomass of rotifers inside or near the cages was higher than that in areas more distant, while that of the cladocerans was the opposite. No significant difference of copepod density or biomass was detected between cages and open water. Changes of zoobenthic community were remarkable. At the beginning of fish farming, there were nine zoobenthic taxa inside and 13 outside the cages. Only two saprophilous taxa, chiefly oligochaetes, were present in the cages at the end of the culture. Density and biomass of benthic animals decreased as well. Several bioindices, such as Shannon-Wiener index, Simpson index, and Margelef index, also exhibited a declining tendency. Through this study, the authors are of the opinion that mass-input of exogenous nutrients may cause negative effects on water quality in areas from the cage to a distance of 50 m outwards. (C) 2003 Elsevier B.V. All rights reserved.

The phylogeny of the Syndermata (Rotifera: Monogononta, Bdelloidea, Seisonidea; Acanthocephala: Palaeacanthocephala, Eoacanthocephala, Archiacanthocephala) is key to understanding the evolution of acanthocephalan endoparasitism from free-living ancestors. In the present study, maximum likelihood, distance/neighbor-joining, and maximum parsimony analyses have been carried out based on 18S rDNA data of 22 species (four new sequences). The results suggest a monophyletic origin of the Eurotatoria (Monogononta + Bdelloidea). Seison appears as the acanthocephalan sistergroup. Palaeacanthocephala split into an Echinorhynchus-and a Leptorhylnchoides-group, the latter sharing a monophyletic origin with the Eoacanthocephala and Archiacanthocephala. As inferred from the phylogeny obtained acanthocephalan endoparasitism evolved from a common ancestor of Seison and Acanthocephala that lived epizoically on an early mandibulate. Probably, an acanthocephalan stem species invaded the mandibulate host, thus establishing an endoparasitic lifestyle. Subsequently, vertebrates (or gnathostomes) became part of the parasite's life cycle. In the stem line of the Archiacanthocephala, a terrestrial life cycle has evolved, with an ancestor of the Tracheata (Insecta, Myriapoda) acting as intermediate host.

A survey on phytoplankton:zooplankton biomass ratios was performed in 342 Norwegian lakes, covering a wide range in lake size and productivity (total phosphorus: 3-246 [mu]g l-1), but with most localities being oligo- to mesotrophic. Mean phytoplankton biomass was 88 [mu]g C l-1, yet with the majority below 50 [mu]g C l-1 and a median of 25 [mu]g C l-1. Total zooplankton biomass displayed a mean and median of 37 and 26 [mu]g C l-1, respectively. Cladocerans were by far the dominant group, making up a median of almost 60% of total zooplankton biomass. Total zooplankton biomass as well as that of major aggregated metazoan taxa (cladocerans, calanoid copepods, cyclopoid copepods and rotifers) all showed a positive, but weak correlation with total phytoplankton biomass. These weak correlations suggest that algal biomass pet se is a poor predictor of zooplankton biomass. An average phyto-:zooplankton biomass ratio (C:C) of 2.8 (SD[plus or minus]4.7) was found. 30% of the lakes had a phyto-:zooplankton biomass ratio below unity. While there was no correlation between the phyto-:zooplankton biomass ratio with increasing productivity in terms of P concentration, there was a higher biomass ratio in lakes with high fish predation pressure. The low ratio of phyto-:zooplankton biomass suggest major requirements from non-algal sources of C in the zooplankton diet. The need for dietary subsidizing is also supported by the fact that more than 75% of the lakes had algal biomass less than the estimated threshold for net positive growth of zooplankton, although it should be kept in mind that a high share of picoplankton would imply an underestimation of autotroph biomass in these lakes. Since the C-deficiency apparently is most pronounced in oligotrophic systems, it contradicts the view that the detritus pathways plays a predominant role in highly productive systems only, but while the source of detritus probably is mostly of autochthonous origin in eutrophic lakes, allochthonous detritus will be more important in oligotrophic systems.

The objective of this study was to evaluate the chronic lethal and sublethal aquatic toxicity effects associated with the phytoremediation of water contaminated with 2,4,6-trinitrotoluene (TNT) by the wetland plant species Myriophyllum aquaticum (parrot feather). Rotifers (Brachionus calyciflorus) feeding on an algal species (Nannochloropsis spp.) were used as the aquatic test organisms. Continuous flow laboratory microcosms were used to quantify effects on rotifer populations from TNT and the primary degradation product aminodinitrotoluene (ADNT) during and after phytoremediation. Rotifer demographic parameters from life tables, including survivorship, fecundity, reproductive values, net reproductive rate, generation time, intrinsic growth rate, and life expectancy, were used as measures of treatment effects. High-performance liquid chromatography analyses were performed to determine nitroaromatic concentrations. Results from this study have revealed significant differences in rotifer demographic parameters between microcosms with elevated initial TNT concentrations. Significant differences in demographic parameters also existed between the microcosms that did and did not receive phytoremediation treatment and the control microcosms. Study results have indicated that TNT phytoremediation via artificial wetlands not only may clean up hazardous waste at munitions sites but also may encourage the growth of aquatic populations such as rotifers.

The rotifer Brachionus plicatilis was fed in experimental conditions with a small celled (2-5 mum) Chlorella sp. and a large celled (16-22 mum) Asteromonas gracilis algae. The specific growth rate (SGR) of rotifers fed Asteromonas (maximum 0.79) was statistically higher than that for rotifers fed Chlorella (maximium 0.61). The filtration and ingestion rates using different rotifer and algal densities exhibited certain maxima depending on the species, the cell density and the condition of the rotifers. The filtration rate was higher with Asteromonas and, although ingestion rate was lower than with Chlorella, the ingestion in terms of cell volume was 10-fold higher. It seems that B. plicatilis ingests the larger cell diameter algal species more efficiently than the smaller species that is usually used for its mass culture.

The embryonic developmental period (De), pre-reproductive period (Dp), the least generation time (Tg), body size of juveniles and adults, egg volume and relative egg volume of three strain Brachionus angularis from Qingdao, Guangzhou and Wuhu were studied with Scenedesmus obliquus at 2.4x106 cells[center dot]ml-1 as the rotifers' food at 25[degree]C. We found that there were significantly different in De, Dp and Tg of three strains. De of WH strain was the top, and subsequently was GZ strain and QD strain. QD strain had the longest Dp, but GZ strain had the shortest. Tg in GZ strain was the shortest, and QD strain, and WH strain were longer, respectively, but no significantly difference existed in the later two. De tended to decrease as the relative egg volume increased in the three strains. Body size at the same stage in pre-reproductive period of three strains was significantly different. WH strain had the largest body size during all of the stages. The relationships between body size and the age of the juvenile of QD, GZ and WH strain were all curvilinear. The variance of the neonates and the adults was 244.24% in WH strain, and 182.89%, 156.28% in QD and GZ strain, respectively. The adults' body size, egg size, and relative egg size was significantly different in three strains.

Three water bodies of contrasting trophic status located at Hope Bay (Antarctic Peninsula) were studied during the summer of 1999, analysing all of their planktonic communities (zooplankton, phytoplankton and bacterioplankton) and their main limnological features. Important differences associated with their trophic conditions were found among lakes. At one extreme of the gradient, in the most oligotrophic lake (Lake Chico), the nektobenthic copepod Boeckella poppei and the rotifer Philodina gregaria were dominant in the open waters, and copepods presented a single reproductive event (univoltine life cycle); phytoplankton exhibited the lowest densities, dominated by nanoplanktonic Chrysophyceae and picocyanobacteria. In the meso-eutrophic Lake Boeckella, B. poppei, the dominant zooplankter, exhibited a multivoltine life cycle; phytoplankton were mainly represented by nanoplanktonic species of Volvocales, alternating with flagellate Chrysophyceae, and a great abundance of picocyanobacteria. In the hypertrophic Pingui Pond, zooplankters were exclusively represented by bdelloid rotifers and ciliates; phytoplankton samples included some strictly planktonic species (Volvocales), a great proportion of picocyanobacteria and many typically benthic species (oscillatorians and diatoms) due to the shallowness of the water body. Bacterioplankton densities did not show important differences among lakes, but fluctuations, probably associated with a top-down control, were observed in the hypertrophic pond. This paper constitutes the first survey concerning all the Planktonic compartments of water bodies of different trophic status at Hope Bay describing the relative contributions of autotrophic and heterotrophic components to their food webs.

Notable records of rare Rotifera are presented and their geographical distribution, autecology, and taxonomy is discussed. All species are new to Austria, others are new to Europe or the Palaearctic. Numerous records of Cephalodella edax and Synchaeta verrucosa indicate a wider distribution of these little known pelagic species, while findings of Ascomorpha tundisii, Cephalodella evabroedae and Lecane elegans reveal highly disjunct distributional patterns.

Although over 40 years of theory have addressed how evolutionary processes can affect the ecology of predator-prey interactions, few empirical data have addressed the same issue. Shertzer et al. and Yoshida et al. have recently combined manipulative experiments with mathematical models to demonstrate that evolutionary change in an algal prey strongly affects community dynamics with their rotifer predator. These studies contribute to recent developments in community genetics and the diversity-stability debate.

Cryptobiosis is an ametabolic state of life entered by some lower organisms (among metazoans mainly rotifers, tardigrades and nematodes) in response to adverse environmental conditions. Despite a long recognition of cryptobiotic organisms, the evolutionary origin and life history consequences of this biological phenomenon have remained unexplored. We present one of the first theoretical models on the evolution of cryptobiosis, using a hypothetical population of marine tardigrades that migrates between open sea and the tidal zone as the model framework. Our model analyses the conditions under which investments into anhydrobiotic (cryptobiosis induced by desiccation) functions will evolve, and which factors affect the optimal level of such investments. In particular, we evaluate how the probability of being exposed to adverse conditions (getting stranded) and the consequences for survival of such exposure (getting desiccated) affects the option for cryptobiosis to evolve. The optimal level of investment into anhydrobiotic traits increases with increasing probability of being stranded as well as with increasing negative survival effects of being stranded. However, our analysis shows that the effect on survival of being stranded is a more important parameter than the probability of stranding for the evolution of anhydrobiosis. The existing, although limited, evidence from empirical studies seems to support some of these predictions.

We amplified three kinds of cDNA fragments encoding stress proteins from the rotifer Brachionus plicatilis by polymerase chain reaction in order to investigate the molecular mechanisms underlying mediation of its lifespan. The stress proteins were heat shock protein 70 (HSP70), glucose regulated protein 94 (GRP94) and ubiquitin-conjugating enzyme, which have been suggested to extend the lifespans of fruitfly and yeast. The isolated clones consisted of 579, 776 and 257bp in the above order, respectively, and their deduced amino acid sequences showed 81, 59 and 48% identities, respectively, with corresponding sequences from the nematode Caenorhabditis elegans. As rotifers in the stationary phase can extend their lifespan we subsequently performed northern blot analysis on rotifers both in the exponential and stationary phases. The mRNA levels of HSP70 and GRP94 in the exponential growth phase were 2.5 and 1.6 times higher, respectively, than those in the stationary phase, whereas those of ubiquitin-conjugating enzyme did not differ between rotifers in the two phases. These results suggest that stress proteins are not directly responsible for the extension of rotifer lifespan, but another factor(s) is possibly involved. Our results, however, demonstrated that these genes are useful as molecular markers for monitoring the population growth of rotifer.

Seasonal changes in the abundance of zooplankters and inorganic factors in Kahoku-gata were studied in 1990 and 1991. Horizontal differences were small in all factors. Dissolved oxygen was usually saturated. The density of chloride ions was below 50 mg/L, which shows that Kahoku-gata was freshwater. Three rotifer species, Brachionus diversicornis, Brachionus calyciflorus and Asplanchna sieboldi became abundant. Crustaceans included one branchiopod species, Diaphanosoma brachyurum, and 9 copepod species. Eucyclops roseus, Cyclops vicinus, Thermocyclops taihokuensis, Eodiaptomus japonicus and Schmackeria inopinus became abundant. Of all zooplankters, the highest density was attained by B. diversicornis in spring and summer. Brachionus calyciflorus increased when neither the competitor B. diversicornis nor the predator A. sieboldi was abundant. Brachionus calyciflorus was spined in the presence of A. sieboldi. Crustaceans increased in August and September.

Floodplain systems along rivers are influenced by the hydrological regime of the river to an extent which depends on the degree of connectivity. As a result, the age of water within the system varies widely. Zooplankton development is restricted to areas and periods of higher water age and thus the role of zooplankton in planktonic carbon flow is strongly influenced by the hydrological dynamics. In 1997 and 1998 the plankton community was examined in the floodplain system along the River Danube, at two sections differing in connectivity to the main river. Zooplankton grazing rates and consumption were calculated, using filtration rates from the literature, based on qualitative and quantitative phyto- and zooplankton data. A succession in grazing dominance from rotifers to cladocerans and copepods was found with increasing water age. Maximal carbon flow and impact on algae by grazing rates of >100% (mean 40.5%) were observed at intermediate connectivity, when zooplankton biomass peaked. Mean grazing impact at high connectivity amounted to 2.5%, and at low connectivity 8.8%, of the total phytoplankton biomass. The main grazers were Synchaeta spp., Polyarthra spp., and the small cladoceran, Bosmina longirostris. Herbivory dominated carbon transfer in the planktonic food webs during dynamic conditions. When conditions are stable, additional food pathways (bacterivory, predation) increase in significance and result in an increased biotic control.

The rich faunal diversity of Zooplankton community, which play an important role in the trophic dynamics of freshwater ecosystem, has not been given due attention by the ecologist in the country, due to the non availability of a concise taxonomic literature. Realising this, a detailed programme of work was initiated to work out the species diversity, community structure and dynamics of zooplankton in some freshwater wetlands of southeastern West Bengal. This region of the country, which covers the districts of North 24 Parganas, Calcutta, South 24 Parganas, Hugly, Haora and Mednipur of West Bengal State, located on either side of the major River Ganga near or on Sunderban delta, is very rich in freshwater resources where almost all types of wetlands occur. The studies were carried out for a period of over one decade (1991-2001) in 20 selected wetlands belonging to six different types viz., 1) floodplain oxbow lakes (open and closed types, 11) natural wetlands (jheels), III) urban recreational lakes and ponds, IV) fish culture ponds, V) sewage-fed fish culture ponds and VI) multipurpose village ponds. The zooplankton community was mainly comprised of 89 species belonging to Rotifera Cladocera and Copepoda. A general tropical character was very much visible and most of the species recorded were typically associated with this region of the world representing cosmopolitan : cosmotropical : pantropical elements in the descending order of abundance. The rotifers were represented by highest number of species (43), which constituted nearly 29% of the species reported from West Bengal and 13% of the country's rotifer fauna. This was followed by Cladoceran, represented by 36 species, which constituted 63% of the total cladoceran species known from West Bengal and 32.% of the country's cladoceran fauna. The species diversity of copepods was lowest as only 10 species belonging to both, calanoids and cyclopoids, were recorded. This constituted nearly 50%% of the species known from West Bengal and about 11.3% of total known species of the country. Variations in the diversity of zooplankton in different wetland types was quite evident. Highest number of species of all groups were recorded from Type-I, Oxbow lakes. The density of zooplankton fluctuated widely between the wetlands and was related to the nature of wetlands. Highest density was recorded from village pond where very high organic load and comparatively lower predation pressure resulted in the increased density of a few species of each group. The impact of predation was quite evident in the two fish culture ponds where the density was considerably low. Inspite of very high nutrient load of Sewage-fed bheries, the density of zooplankton species was severely limited. While copepods dominated numerically in oxbow lakes, natural wetlands, village pond and urban lakes, rotifers formed numerically dominant component in the fish culture ponds. All the wetlands were characterized by a set of a few numerically abundant species that controlled the bulk of zooplankton density. The analysis of species richness indices revealed clearly the status of these wetlands. Oxbow takes and natural wetlands, mainly fed by rainwater with abundant macrophytes, exhibited high species richness and on the other hand, sewage-fed fish culture pond, with considerably high organic load, was characterised by lowest diversity. Further, due of their comparatively unpolluted conditions, the oxbow lakes and natural wetlands exhibited a greater similarity in respect of their zooplankton fauna. The analysis has significantly isolated the sewage-fed fish culture ponds, which due to their highly specialised nature, exhibited considerably different conditions.

This study examined the effects of storage time on the fatty acid composition of freshwater Selenastrum capricornutum algal paste under 4 C refrigeration, the fatty acid composition of rotifers fed the fresh and stored algal paste, and the toxicological properties of the algal paste. Microalgae were produced in a hydraulically integrated serial turbidostat algal reactor (HIS-TAR), harvested as a paste, refrigerated and analyzed every 2 wk. Fresh Selenastrum capricornutum paste had almost three times greater concentration of unsaturated fatty acids than saturated fatty acids. Over 50% of the unsaturated fatty acids were made up of n-3 and n-6 fatty acids. Total unsaturated, n-3 group and n-6 group fatty acids decreased (P < 0.05) during storage, including the nutritionally important fatty acids (C20:4n6, C20:5n3, C22:6n3). Rotifers fed 2- and 4-wk-old algal paste had a significantly lower (P < 0.05) total unsaturated fatty acid percentage and significantly greater (P < 0.05) total saturated fatty acids than those fed fresh algae. There were no significant changes in the n-6 group fatty acid level in the 4-wk-old paste feeding study or for the n-3 or n-6 groups in the 2-wk-old paste feeding study as compared to fresh algae. The levels of the three nutritionally important fatty acids (C20:4n6, C20:50, C22:6n3) did not differ between rotifers fed fresh and stored algae. Stored algae did not present toxicity to rotifers and Daphnia at the normal feeding concentration. These results indicated that the use of refrigerated freshwater algal paste for production of rotifers results in live feed with adequate nutritional properties for marine larviculture. This could eliminate the costs associated with production of marine algae, which could be replaced with freshwater algae, and may provide an alternative to cryopreservation.

Dispersal among local communities can have a variety of effects on species composition and diversity at local and regional scales. Local conditions (e.g., resource and predator densities) can have independent effects, as well as interact with dispersal, to alter these patterns. Based on metacommunity models, we predicted that local diversity would show a unimodal relationship with dispersal frequency. We manipulated dispersal frequencies, resource levels, and the presence of predators (mosquito larvae) among communities found in the water-filled leaves of the pitcher plant Sarracenia purpurea. Diversity and abundance of species of the middle trophic level, protozoa and rotifers, were measured. Increased dispersal frequencies significantly increased regional species richness and protozoan abundance while decreasing the variance among local communities. Dispersal frequency interacted with predation at the local community scale to produce patterns of diversity consistent with the model. When predators were absent, we found a unimodal relationship between dispersal frequency and diversity, and when predators were present, there was a flat relationship. Intermediate dispersal frequencies maintained some species in the inquiline communities by offsetting extinction rates. Local community composition and the degree of connectivity between communities are both important for understanding species diversity patterns at local and regional scales.

A study on the horizontal distribution of rotifers (Rotifera) and crustaceans (Cladocera and Copepoda) was conducted in Lake Budzynskic, located in Wiclkopolski National Park, Poland. Zooplankton was sampled six times within 24 hours (31 August-1 September, 1996) from five stations. These were located in a zone of rushes, two zones of submerged macrophytes (Chary and Myriophyllum) and two areas of free water between the vegetation beds. It was observed that the diurnal horizontal distribution of particular groups of zooplankton differs, mostly depending on the particular species of macrophyte. The highest numbers of both rotifers and crustaceans were recorded for the Myriophyllum verticillatum zone, irrespective of the time of the day.

The omnivorous cyclopoid copepod, Mesocyclops thermocyclopoides, perennially found in many lakes and ponds of Delhi, preys on a variety of zooplankton species ranging from protozoans to crustaceans, but its impact on the population dynamics of the prey is variable. I studied in the laboratory the population growth patterns of selected prey species of different taxa- ciliates (Stylonychia notophora, Paramecium caudatum and Pseudourostyla levis), rotifers (Brachionus angularis, B. rubens and B. calyciflorus), and cladocerans (Ceriodaphnia cornuta, Moina macrocopa, and Daphnia similoides) in the presence and in the absence of M. thermocyclopoides. I used the intrinsic rate of natural increase of the prey and a predator impact index to assess the impact of cyclopoid predation. The predator impact was significantly higher on protozoans and cladocerans than on rotifers. The most adversely affected species were C. cornuta, P. caudatum and B. calyciflorus, and the least affected were D. similoides, B. angularis and P. levis. The mortality imposed by the copepod was significantly less (or no mortality) on the seventh day than on the third day in each case. My laboratory studies suggest that the differential impact of predation by M. thermocyclopoides may be one of the determinants of zooplankton community structure in shallow, eutrophic subtropical and tropical water bodies.

Clarification of municipal wastewater was shown to be improved significantly by the addition of cultured bdelloid rotifers. The rate and degree of suspended particle removal were correlated with rotifer number. The size range of unsettled particles suspended in wastewater was determined and found to overlap with the size range of particles consumed by rotifers. Rotifers were shown to have two distinct effects on suspended particles: consumption of biomass due to feeding activity; and improved settling, probably due to enhanced aggregation. These experiments demonstrate the potential for the use of bdelloid rotifers in an enhanced wastewater treatment process, with reduced biomass production and improved effluent clarity.

Eukaryotes able to withstand desiccation enter a state of suspended animation known as anhydrobiosis, which is thought to require accumulation of the non-reducing disaccharides trehalose (animals, fungi) and sucrose (plants), acting as water replacement molecules and vitrifying agents. We now show that clonal populations of bdelloid rotifers Philodina roseola and Adineta vaga exhibit excellent desiccation tolerance, but that trehalose and other disaccharides are absent from carbohydrate extracts of dried animals. Furthermore, trehalose synthase genes (tps) were not found in rotifer genomes. This first observation of animal anhydrobiosis without trehalose challenges our current understanding of the phenomenon and calls for a re-evaluation of existing models. (C) 2003 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Planktonic organisms exhibit diverse morphological, behavioural and life-history responses to the chemical presence of potential predators. Prey organisms have been found to sense such predators via predator-derived kairomones. The induced reactions are assumed to reduce predation risk and thus to be adaptive. Numerous studies have investigated various aspects of inducible defences in different crustaceans, in rotifers, planktonic ciliates and algae. As a first step, we summarise recent work on chemically induced anti-predator defences in morphology, life history and behaviour. Morphological defences have been found in a wide range of different plankton organisms and recent studies on predator-induced morphologies mainly addressed the question of costs for these changes. Life-history responses were mainly studied in cladocerans and several studies have recently addressed some novel topics, such as diapause induction and the influence of predator kairomones on hatching of resting stages. Behavioural anti-predator defences also have been found for several plankton species and are characterised by relatively fast induction times. We further identified four research directions in which substantial progress has been made recently: (I) The effects of simultaneous exposure to infochemicals from different predators and the consequences of a complex chemical environment. Some environmental contaminants, such as synthetic chemicals or heavy metals, have been found to potentially disturb natural chemical communication in aquatic predator-prey systems. (II) The influence of genetic variation on the reaction to infochemicals and its implications. Clonal differences have not only been found for the presence or absence of a certain trait but also with respect to the type of response. (III) The degree to which different types of responses to a specific kairomone are coupled. Recent studies underline the uncoupling of different anti-predator responses of which some have been considered to be coupled. (IV) Studies on the chemical properties and on the metabolic origin of predator kairomones. Substantial progress has been made recently, especially with respect to the identification of predator kairomones that are important for planktonic ciliates. The identification and isolation of kairomones are an important step towards studies addressing the consequences of predator-induced defences on the level of populations, communities and ecosystems. So far most studies have considered effects and consequences on the level of individual prey organisms and studies taking the consequences at higher ecological levels into account are rare.

Photosynthesis and microbial plankton dynamics of two lakes in the Kongsfjorden catchment of Spitzbergen (Svalbard Archipelago, 78[degree]N) were investigated during the summer of 2000. One of the lakes (Tvillingvatnet) served as the water supply for the village of Ny Alesund. The other was a deeper, larger unnamed lake in the Ossian Sarsfjella reserve[long dash]named Lake OS in this study. Both lakes can be classified as oligotrophic on the basis of chlorophyll a and inorganic nutrient concentrations. Chlorophyll a concentrations ranged between 0.33 and 1.65 [mu]g l-1 in Tvillingvatnet and 0.2 and 0.3 [mu]g l-1 in Lake OS. The phytoplankton was dominated by chrysophytes and cryptophytes, with the diatom Rhizosolenia and a number of dinoflagellate species. Rates of photosynthesis were typically low, between 24.5 [mu]g and 1.0 mg l-1 day-1 in Tvillingvatnet (photo-synthetic efficiency 0.004-0.26), and between 3.1 and 29.5 [mu]g l-1 day-1 in Lake OS (photosynthetic efficiency 0.0019-0.0085). Among the phytoflagellates (PNAN) there were a number of mixotrophs which reached their peaks of abundance before other PNAN. Mixotrophy appeared to provide a competitive advantage. Grazing rates for the mixotroph Dinobryon ranged between 0.063 and 1.12 pg C cell-1 day-1 in Lake OS and between 0.22 and 1.11 pg cell-1 day-1 in Tvillingvatnet, with rates increasing between July and August. However, Dinobryon removed less than 1% of bacterial biomass day-1, while the heterotrophic nanoflagellates (HNAN) removed up to 28% of bacterial biomass day-1. Bacterial concentrations were low, with a maximum of 28.8x108 l-1 in Tvillingvatnet and 23.6x108 l-1 in Lake OS. Ciliated protozoan and rotifer diversity in the plankton was low.

Laboratory populations of two Brachionus calyciflorus strains were cultured on five levels (3.0, 6.0, 9.0, 12.0, and 15.0x106 cells/ml) of Chlorella pyrenoidosa. There were highly significant effects of both food level and strain, independently and in interaction, on population growth rate, body size, and egg size.

Laboratory populations of two Brachionus calyciflorus strains were cultured on five levels (3.0, 6.0, 9.0, 12.0, and 15.0 X 10(6) cells/ml) of Chlorella pyrenoidosa. There were highly significant effects of both food level and strain, independently and in interaction, on population growth rate, body size, and egg size.

In the PHYTO-PAM phytoplankton analyzer the minimal fluorescence of dark-adapted samples (F0) was assessed, which gives direct information on the chlorophyll-a content. Clearance rates (CR) of Daphnia and Brachionus were calculated from a decrease in chlorophyll-a concentration using the PHYTO-PAM fluorometer for non-sacrificial sampling of chlorophyll-a. Clearance rates of Daphnia were measured and compared with those based on the cell-counts method using an electronic particle counter (Coulter counter). Chlorophyll fluorescence-based CR for Daphnia magna were very strongly correlated with Coulter-based CR, signifying the potential suitability of the PHYTO-PAM in grazing experiments. A procedure for determination of rotifer clearance rates was developed and the effects of rotifer density, duration of the grazing period, and food concentration on CR were investigated. Between 10 and 30 rotifers in 2.5 ml food suspension (i.e. 4-12 rotifers per ml) appeared optimal for calculating CR. The application of the deconvolution of F0-spectra in food selectivity experiments was evaluated using various mixtures of the green alga Scenedesmus obliquus and the cyanobacterium Microcystis aeruginosa fed to Brachionus. CR for Brachionus on M. aeruginosa were lower than on S. obliquus but this was not caused by toxicity, because no mortality was observed. The higher CR on Scenedesmus than on Microcystis in the mixtures suggested selectivity. The importance of digital suppression of background fluorescence is highlighted in additional experiments with Daphnia feeding on mixtures of Microcystis and Scenedesmus, or on Microcystis alone. Without background correction of filtered samples, negative clearance rates were obtained for the 'blue' Microcystis signal. Soluble fluorescing compounds of cyanobacterial origin, phycocyanin, were released from the Daphnia and contributed 40% to the overall-fluorescence. Deconvolution of F0-spectra for the determination of chlorophyll-a using the PHYTO-PAM appears to be a suitable tool for determination of rotifer CR even at very low food concentrations. A drawback of the method is that rather high rotifer densities are required. The required grazing period, however, is shorter than for cell-count methods, the method is sensitive, clearance rates can be measured at low food concentrations (<0.1 mg C l-1) and information on selective feeding can be obtained.

During the Lake Towada survey from April through October 1998, we measured primary production at shore and offshore stations, and calculated crustacean zooplankton production from samples collected at the offshore station. We then analyzed these data and compared them with commercial fishery data in order to discuss the energy flow in this lake where kokanee (Oncorhynchus nerka) fisheries are one of the main businesses. At all stations, primary production was relatively high: 150-300 mg Cm-2 day-1 in April-mid-June and lower at ca. 100 mg Cm-2 day-1 thereafter. The variation in primary productivity could largely be explained by multiple regression models that included phytoplankton biomass and ambient nutrient conditions as independent variables. Among zooplankton, rotifers had their peak abundance in May, before the crustacean zooplankton (Daphnia longispina, Bosmina longirostris, and Acanthodiaptomus pacificus) population was well established. D. longispina dominated the crustacean zooplankton community in terms of biomass and production; their production during the study period made up 80% of crustacean community production (19.6 g dry-wt m-2), which was 40% of primary production during the survey. In July, when the abundance of D. longispina was particularly high, their daily production slightly exceeded daily primary production, which resulted in ca. 30% and 75% reduction in the amount of particulate organic carbon and chlorophyll a, respectively, during this period. The community ingestion rate of crustacean zooplankton, calculated from their daily production (D. longispina accounted for 90%) and the assumption that their gross production efficiency (K1) was 60%, could roughly explain this reduction of particulate matter, corroborating previous studies that the grazing of D. longispina can significantly improve the water transparency of this lake. The catch of kokanee and pond smelt (Hypomesus transpacificus nipponensis, another important fish in the lake) during the survey corresponded to 1.1% of crustacean community production, and corresponded to 0.45% of the primary production, which is one of the highest recorded values. Bearing in mind that D. longispina was the major food item of planktivorous fish such as kokanee and pond smelt, the present study suggests that the energy transfer from phytoplankton to zooplankton to fish is outstandingly efficient, compared with other aquatic ecosystems, when D. longispina dominates in the lake.

In aquatic environments heterotrophic flagellates are an important component within the microbial loop and the food web, owing to their involvement in the energy transfer and flux and as an intermediate link between bacteria and primary producers, and greater organisms, such as other protists and metazoan consumers. In the microbial loop heterotrophic flagellates highly contribute to fast biomass and nutrient recycling and to the production in aquatic environments. In fact, these protists consume efficiently viruses, bacteria, cyanobacteria and picophytoplankton, and are grazed mainly by other protists, rotifers and small crustaceans. In this paper the knowledge about these unicellular organisms is reviewed, taking into particular account their ecological relationships and trophic role within the plankton community of marine and freshwater environments.

Ancient asexual animal groups, such as bdelloid rotifers and darwinuloid ostracods, are excellent model organisms to study the effects of long-term asexuality. However, the absolute length of time that these groups have been fully asexual is mostly ignored. In the case of the darwinuloid ostracods, the fossil record shows that sexual reproduction disappeared almost completely after the end of Permian mass extinction (ca. 245 Myr ago), although several putative records of males from the Mesozoic obscure the exact time-frame of obligate asexuality in darwinuloids. Here, we re-examine the Mesozoic darwinuloid records, with regard to the reproductive mode of the assemblages. Three criteria to distinguish males in fossil populations (lack of brood pouch, position of muscle scars and size dimorphism) are used here to test for the presence of males in darwinuloid assemblages. A large, well-preserved assemblage of Darwinula leguminella (Forbes 1885) from the latest Jurassic (ca. 145 Myr ago) of England is found to be markedly variable in size and shape, but nevertheless turns out to be an all female assemblage. The exceptional preservation of the material also allows the re-assignment of this species to the extant darwinuloid genus Alicenula. All other putative dimorphic darwinuloid records from the Mesozoic are re-examined using the same criteria. The hypothesis that these assemblages represent bisexual populations is rejected for all post-Triassic (ca. 208 Myr ago) records.

The bioencapsulation of live bacteria in the rotifer Brachionus plicatilis was determined under monoxenic conditions. The first objective was to evaluate the microhiota of the rotifer during intensive production and to obtain sterile rotifer cultures starting from adult females or amictic eggs using PVP-Iodine, Hydrogen peroxide or antibiotic mixtures. In the rotifers. the proportion of vibrios increased significantly during the mass production, displacing other unidentified marine bacteria. Rotifers, in the absence of culturable bacteria were obtained starting from amictic eggs and using Trimetroprim-sulfametoxasole (Bactrim Roche[registered trademark]) at 10 ml 1-1. The effect of members of Vibrionaceae on the survival and growth rate of rotifers was determined under monoxenic conditions. The survival of rotifers was not affected in the presence of different isolates, while amictic egg formation occurred and the populations increased when the strains Vibrio proteolyticus C279 and Aeromonas media C226 were tested. All isolates were successfully incorporated in the rotifers, since there was no significant difference between the numbers of bioencapsulated cells of different strains of isolates. The results show that it is possible to replace the microbial community in rotifer cultures, started from disinfected amictic eggs, with selected bacterial strains. This could be used as a tool for future studies to reveal the role of specific bacteria on first larval stages of marine fish species.

We describe several uncommon contaminants presumably derived from the tap water used in the staining procedure of cytological specimens. We would like to draw attention to the occasional presence of diatoms and fragments of rotifers in cytological specimens. Whilst most of these entities are harmless curiosities, they may cause concern as to their nature and significance.

The present work was carried out during summer (May & June) and rainy period (October, November and December) on Thirukkulam pond (Mannampandal). Qualitative analysis of zooplankton population of the pond indicates occurrence of 21 species during both summer and rainy seasons. The major groups of zooplankton in descending order are Copepoda, Cladocera, Rotifera and Ostracoda. Higher density of zooplankton population was noted during rainy season. Among the 21 zooplanktonic species, 4 from Protozoa, 2 from Porifera, 5 from Rotifera, 4 from Cladocera and 3 each from Ostracoda and Copepoda have been recorded. Simultaneously physico-chemical parameters such as both atmospheric and surface temperature, transparency, pH, CO2 and DO values were recorded. All the values of physico-chemical parameters showed slight variations during the summer and rainy seasons.

In oligotrophic Andean lakes, omnivorous calanoid copepods are the dominant zooplankters and, remarkably, phototrophic nanoflagellates and mixotrophic ciliates are the prevailing primary producers. In Lake Rivadavia (Patagonia, Argentina), the centropagids Boeckella michaelseni and Parabroteas sarsi coexist with the large cladoceran Daphnia middendorffiana. The particular feeding modes of these zooplanktonic species probably impact differentially on the microbial community. To determine the effect of predation on the pelagic microbial food web in this lake, we conducted a series of field experiments manipulating different zooplankton structures in 21 enclosures. The results showed that the presence of B. michaelseni and rotifers depressed ciliates and nanoflagellates, but did not affect autotrophic picoplankton and total bacteria abundances. In contrast, the presence of Daphnia was decisive in decreasing autotrophic picoplankton abundances. P. sarsi was observed to prey on B. michaelseni copepodites and adults and a weak cascading effect on the microbial fraction could be detected.

In January 2001, we surveyed streams and ponds above 300 m a.s.l. in Taylor Valley, South Victoria Land, Antarctica. One pond was examined in detail. Organic materials covered nearly 100% of the adjacent soil to 5-20 m from the shore, with intermittent patches to 80 m. Organic matter averaged 257 g C/m2, and totaled 1,388 kg organic C on the soil around the pond. Soil-moisture content (0.56-12.41%) decreased with distance from shore, whereas pH (7.8-10.8) increased with distance. Electrical conductivity was lowest in the soils <10 m from the pond (416[plus or minus]94 [mu]S/cm). Mineral soil organic C and total N concentrations were greatest between 10 and 30 m from the edge of the pond (1.21[plus or minus]0.37 and 0.13[plus or minus]0.05 mg/g soil, respectively). Soil invertebrates were present in only 50% of samples and included tardigrades, rotifers, and two nematodes, Scottnema lindsayae and Plectus antarcticus. A non-parametric, discriminant function analysis based on soil moisture, soil organic carbon, and electrical conductivity correctly predicted 87.0% of sites that had invertebrates and 70.8% of sites for which invertebrates were absent. Tardigrades, rotifers, and P. antarcticus were found only in the wettest soils nearest the pond whereas S. lindsayae was restricted to drier soils further from shore. Other ponds and streams also showed substantial accumulations of organic matter, suggesting that upland wetlands serve as resource islands in these polar deserts that provide a source of organic matter to nearby soils.

1. We investigated the numerical response, functional response and prey preference of Asplanchna sieboldi to five different prey brachionids. We also analysed the feeding behaviour of the predator in terms of encounters, attacks, capture and prey ingested per unit time.2. The five prey species (Brachionus havanaensis, B. rubens, B. patulus, B. macracanthus and B. calyciflorus) differed in their body size and spine length.3. The population growth rates of A. sieboldi ranged from 0.074 +/- 0.03 to 0.431 +/- 0.02 depending on prey type and density. There was a significant impact of the spine length rather than body size per se on the population growth rates of the predator.4. The maximum number of prey consumed depended on both body size and spine length. In the functional response analyses, the plateau was reached at a prey density of 4-8 ind. mL(-1).5. There was a significant impact of prey density on the prey preference of the predator.

In the present study, two small lakes on the margins of the River Cuiaba were analyzed regarding taxonomic composition and population densities of the zooplankton. Diversity was evaluated for two groups, Rotifera and Cladocera; sampling was carried out on two dates: 2 March 1999, in the rainy season, and 25 August 1999, in the dry season. Seventy-nine rotifer taxa, 30 cladoceran taxa, and 6 copepod taxa were found. Comparing the species identified in the present study with those recorded by other authors for several water bodies in Mato Grosso and Mato Grosso do Sul states, it was found that 9 species of Cladocera, 2 of Copepoda, and 14 of Rotifera are new records for the region. The most abundant rotifer species were Keratella cochlearis, Brachionus angularis, Polyarthra vulgaris, and Keratella americana. Moina minuta and Bosminopsis deitersi were dominant among the cladocerans, and Notodiaptomus transitans and N. devoyorum among the copepods. Comparing both lakes, the greatest species richness of both Rotifera and Cladocera was observed in Lake Souza Lima, during the rainy season. This is probably linked to the fact that the littoral region of this lake is densely colonized by macrophytes. The lake also has better environmental conditions since it does not receive domestic sewage inputs, as does Lake Parque Atalaia. The diversity of the Rotifera was markedly low in Lake Parque Atalaia, during the dry season, again perhaps linked domestic sewage input found in this water body.

Ancient asexuals [long dash] organisms that have lived without sex for millions of years [long dash] offer unique opportunities for discriminating among the various theories of the maintenance of sex. The last few years have seen molecular studies of a number of putative ancient asexual lineages, including bdelloid rotifers, Darwinulid ostracods, and mycorrhizal fungi. To help make sense of the diverse findings of such studies, we present a review and classification of the predicted effects of loss of sex on the eukaryotic genome. These include: (1) direct effects on the genetic structure of individuals and populations; (2) direct effects on the mutation rate due to the loss of the sexual phase; (3) decay of genes specific to sex and recombination; (4) effects of the cessation of sexual selection; (5) dis-adaptation due to the reduced efficiency of selection; and (6) adaptations to asexuality. We discuss the utility of the various predictions for detecting ancient asexuality, for testing hypotheses of the reversibility of a transition to asexuality, and for discriminating between theories of sex. In addition, we review the current status of putative ancient asexuals.

Long-term coevolution of transposable elements (TEs) in sexual hosts leads to evolution of extremely active and dangerous mutagens kept in tenuous check by host-derived mechanisms and via natural selection against TE-rich genomes. To the extent that sexual reproduction and recombination are important in maintaining a stable TE copy number and a tolerable mutation load, the switch to clonality from sexual reproduction can be extremely damaging and, generally, should lead to clonal lineage extinction. Surprisingly however, the loss of powerful selective mechanisms constraining TEs can be beneficial in the short-term by immediately eliminating selective load and possibly promoting the early success of clonal lineages. The clonal lineages that do survive in the long-term must find a way to eliminate or domesticate TEs. Indeed bdelloid rotifers, which are ancient asexuals, do appear to have lost most of the otherwise wide-spread TEs and might have domesticated others. The path to this TE-free haven is anything but clear at the moment. We have considered a novel scenario of instantaneous inactivation of TEs by starting off with a genome carrying repressive host alleles for all TEs in the genome. We show that such a scenario appears plausible and provide some limited empirical evidence in its support. (C) 2003 The Linnean Society of London.

This study clarifies the identity and development of the male in the life cycle of Symbion pandora. The male is not produced directly by the feeding stage, as previously thought, but arises as a distinct individual from budding cells inside an intermediate stage named the Prometheus larva. The morphology and the development of the two distinct stages are described with light and electron microscopy. Furthermore, the following terminology is suggested to clearly distinguish between the different individuals: 1) the Prometheus larva, which is the free-swimming individual being produced inside the feeding stage; 2) the attached Prometheus larva on the feeding stage, which mostly degenerates following settlement, except for the internal budding cells; and 3) the dwarf male, which is the ciliated, sexually mature stage. The budding cells inside the attached Prometheus larva usually develop two internal dwarf males. Each dwarf male is heavily ciliated and has a well-developed nervous system with a relatively large brain, numerous gland and muscle cells, testis with bundles of sperm, and one penial structure. The male lacks a gut, as in the other free stages in the life cycle of Symbion pandora. This study also indicates that the dwarf male is freed from the attached Prometheus larva. Copulation, which has not been observed yet, probably takes place between a free-swimming male and the female, either while the female is released or afterwards. (Copyright 2003 Wiley-Liss, Inc.)

The Commission has ruled that the homonymy between the family-group names CLARIIDAE Kutikova, Markevich & Spiridonov, 1990 (Rotifera) and CLARIIDAE. Bonaparte, 1846 (Osteichthyes) is removed by emending the spelling of the rotifer family-group name by adopting the full genus name as the stern, giving the corresponding family-group name CLARIAIDAE: Kutikova, Markevich & Spiridonov, 1990. The fish name CLARIIDAE. Bonaparte, 1846 remains unchanged.

1. The coexistence of five cryptic species of the rotifer species complex Brachionus plicatilis was investigated in four coastal Mediterranean ponds. Monthly sampling was undertaken for 15 months and species were characterised using allozyme electrophoresis.2. We describe species-diagnostic allozyme loci that can be used for rapid identification of these species.3. The five species overlapped to some extent in their temporal use of the ponds, although some seasonal segregation was observed.4. The match between temporal and spatial distribution and limnological conditions suggested ecological specialisation in some cases, although we found striking examples of extensive seasonal overlap.5. Our results indicate that sympatry of cryptic rotifer species is largely because of seasonal ecological specialisation, which allows seasonal succession and partitioning of resources. The processes that might be involved in the long periods of overlapping seasonal distributions of species which are potentially competitors are discussed. This example illustrates that the 'paradox of the plankton' is more the rule than the exception.

Based on two mesocosm experiments and 10 in vitro predation experiments, this work aimed to evaluate the impact of nutrient supply and Chaoborus predation on the structure of the zooplankton community in a small reservoir in Cote d'Ivoire.During the first mesocosm experiment (M1), P enrichment had no effect on phytoplankton biomass (chlorophyll a) but significantly increased the biomass of some herbivorous zooplankton species (Filinia sp, Ceriodaphnia affinis). During the second experiment (M2), N and P enrichment greatly increased phytoplankton biomass, rotifers and cladocerans (C. affinis, C. cornuta, Moina micrura and Diaphanosoma excisum). In both experiments, nutrient addition had a negative impact on cyclopoid copepods.Larger zooplankton, such as cladocerans or copepodites and adults of Thermocyclops sp., were significantly reduced in enclosures with Chaoborus in both mesocosm experiments, whereas there was no significant reduction of rotifers and copepod nauplii. This selective predation by Chaoborus shaped the zooplankton community and modified its size structure. In addition, a significant Chaoborus effect on chlorophyll a was shown in both experiments.The preference of Chaoborus for larger prey was confirmed in the predation experiments. Cladocerans D. excisum and M. micrura were the most selected prey. Rotifer abundance was not significantly reduced in any of the 10 experiments performed.In conclusion, both bottom-up and top-down factors may exert a structuring control on the zooplankton community. Nutrients favoured more strictly herbivorous taxa and disadvantaged the cyclopoid copepods. Chaoborus predation had a strong direct negative impact on larger crustaceans, favoured small herbivores (rotifer, nauplii) and seemed to cascade down to phytoplankton.

1. Based on two mesocosm experiments and 10 in vitro predation experiments, this work aimed to evaluate the impact of nutrient supply and Chaoborus predation on the structure of the zooplankton community in a small reservoir in Cote d'Ivoire. 2. During the first mesocosm experiment (M1), P enrichment had no effect on phytoplankton biomass (chlorophyll a) but significantly increased the biomass of some herbivorous zooplankton species (Filinia sp, Ceriodaphnia affinis). During the second experiment (M2), N and P enrichment greatly increased phytoplankton biomass, rotifers and cladocerans (C. affinis, C. cornuta, Moina micrura and Diaphanosoma excisum). In both experiments, nutrient addition had a negative impact on cyclopoid copepods. 3. Larger zooplankton, such as cladocerans or copepodites and adults of Thermocyclops sp., were significantly reduced in enclosures with Chaoborus in both mesocosm experiments, whereas there was no significant reduction of rotifers and copepod nauplii. This selective predation by Chaoborus shaped the zooplankton community and modified its size structure. In addition, a significant Chaoborus effect on chlorophyll a was shown in both experiments. 4. The preference of Chaoborus for larger prey was confirmed in the predation experiments. Cladocerans D. excisum and M. micrura were the most selected prey. Rotifer abundance was not significantly reduced in any of the 10 experiments performed. 5. In conclusion, both bottom-up and top-down factors may exert a structuring control on the zooplankton community. Nutrients favoured more strictly herbivorous taxa and disadvantaged the cyclopoid copepods. Chaoborus predation had a strong direct negative impact on larger crustaceans, favoured small herbivores (rotifer, nauplii) and seemed to cascade down to phytoplankton.

Resting stages (cysts) of Artemia franciscana, Hexarthra fennica and Fabrea salina were exposed for two periods (acute and chronic exposures) to different concentrations of five aquaculture disinfectants (formalin, sodium hypochlorite, potassium permanganate, organic iodine, copper sulphate). The effects of chemical treatments were ranked according to their action on cyst hatching: total inhibition (no cyst hatching), heavy inhibition (significant decrease of cyst hatching), alteration of hatching synchrony, and occurrence of anomalous hatching (death of emerging individuals or birth of malformed organisms). Resting-stage viability was not completely impaired by disinfectant exposures at the ordinary doses used in aquaculture, so that usual treatments are possibly ineffective against the protist and metazoan cysts potentially present in breeding systems. On the other hand, the high resistance shown by cysts suggests the possibility of using these chemicals in live-feed disinfection.

We sampled zooplankton and benthic macroinvertebrate assemblages in 30 shallow natural lakes to determine the effects of the environment (i.e., habitat and fish abundance) on invertebrates. Zooplankters were identified to genus, and up to 120 individuals per genus were measured. Macroinvertebrates were identified to order, class, or family. Fish communities were also sampled. Relative abundances of zooplankton and macroinvertebrates were low at increased chlorophyll a concentrations, although mean zooplankton length increased with total phosphorus, possibly because of an increased proportion of microzooplankton (rotifers and copepod nauplii) at higher phosphorus levels. Canonical correspondence analysis revealed that zooplankton and macroinvertebrate abundance was influenced by submersed vegetation coverage, whereas zooplankton abundance and size structure were also related to productivity (i.e., chlorophyll a and total phosphorus). However, relative abundance of fish species or fish feeding guilds was not strongly correlated with zooplankton or macroinvertebrate abundance or zooplankton size structure. Physical habitat (e.g., vegetation coverage) may exert substantial influences on invertebrate assemblages in these lakes, possibly providing a refuge from fish predation.

We analyzed three species of Lecane, a littoral rotifer, for susceptibility to six metals and four organic toxicants using a fluorometric assay based on inhibition of activity of the enzyme phospholipase A2. The metallic toxicants that we tested included Cd, Cr, Cu, Pb, Hg (as HgCl2), and Ti; the organic toxicants included benzene, ethyl acetate, toluene, and vinyl acetate. The three species differed greatly with respect to their susceptibility to the various toxicants. Lecane quadridentata, for example, was particularly sensitive to the four organic compounds (median effective concentration values [EC50] ranged from 6.6x10-4-0.987 mg/L). Lecane luna, in contrast, seemed particularly sensitive to metals (EC50 values ranged from 2x10-6-1.92 mg/L). Lecane hamata was relatively insensitive to organic solvents (EC50 values ranged from 4.25-126.5 mg/L).

The ecotonal zone was created by psammolittoral, emerged macrophytes in eulittoral and littoral, and submerged vegetation in littoral. Immigration of typical plankton species of Rotifera to the psammon communities occurred. The highest density of rotifers was found in psammolittoral zone, lower in littoral and the lowest in eulittoral zone. The highest biodiversity was found in eulittoral and littoral zones of lakes with well-developed pond type phytolittoral.

Nutrient content of plants is low relative to that of herbivores. Dietary nutrients can limit the growth and reproduction of herbivores. We studied life history consequences and starvation resistance for a common planktonic rotifer, Keratella cochlearis, feeding on algae grown on nutrient-limited media. A strain of Cryptomonas was grown on three types of growth medium with nitrogen (N) and phosphorus (P) adjusted to produce N-limiting, P-limiting, and nutrient-sufficient conditions. The analysis of nutrient content of Cryptomonas cells grown on nutrient-limited conditions showed that those algae exhibited higher P content than algae growing on a nutrient-sufficient medium. However, Cryptomonas reached lower densities in nutrient-limited media. The life history responses of Keratella to food quality were examined with low and high food availability. Our study showed that the interaction of food quantity and quality had a significant effect on rotifer growth rates. We observed, at low food levels, that Keratella growth rates were highest when the algae were grown under P limitation. The lowest rotifer growth rates were obtained when the rotifer fed on Cryptomonas grown in nutrient-sufficient conditions. Our study also showed that starvation resistance was higher for those rotifers fed on N-limited Cryptomonas. In natural situations, rotifers could even grow better under nutrient-limited conditions if this group of algae is dominant in the phytoplankton community. Moreover, differences in starvation resistance could be critical in determining competitive outcome and community structure in nutrient-variable environments.

Different species of flora and fauna exhibit variation in their response to any alteration in the environment and have indicator values. Hence, the high degree of aquatic pollution results in dominance of pollution tolerant species, which leads to change in biodiversity of the specific lake. The three lakes studied showed abundance of three different species of macrophytes namely Lemna minor, Pistia stratiotes and Eichhornia crassipes. High fluctuation in DO (1.539.69 mg/L), CO2 (0-28.16 mg/L), PO4 -P (0.0029-0.3000 mg/L) and NO3-N (0.086-0.330 mg/L) were found. Similarly, from total 35 species of phytoplankton observed, 19 were common to uninfested and infested lakes but 16 species were seen only in infested lakes and 12 only in uninfested lakes. Similarly, among the zooplankton rotifers, which are considered the pollution indicators, 10 species were found in infested lakes out of which 4 were common to infested and uninfested lakes, proving the change in biodiversity.

We desiccated bdelloid rotifers (Macrotrachela quadricornifera), submitting the animals to four desiccation procedures (protocols A, B, C, D) that differed in the rate of water evaporation, in the time of desiccation, and in the substrates provided. We observed external morphological changes of the rotifer bodies during drying with scanning electron microscopy and, in parallel, assessed rates of recovery after a 7-day period of dormancy. Two protocols produced disorganized morphologies of the anhydrobiotic animals, with no (A) or very poor (B) recovery. Protocols C and D gave rather high rates of recovery and dry rotifers appeared unaltered and well organized. The different protocols affected rotifer morphology during the 7-day anhydrobiosis and rates of recovery after the 7-day anhydrobiosis; high recovery rates corresponded to well-organized morphologies of anhydrobiotic bdelloids, suggesting that a proper contraction of the body into a tun shape and probably a rigorous packing of internal structures are necessary for survival after anhydrobiosis. These features are affected by the time between water shortage and full desiccation, but also by the surrounding relative humidity and by the nature of the substrate. Possible adaptations of anhydrobiotic rotifers are discussed.

Bdelloid rotifer research in Australia is reviewed, the current systematic status of the group is summarized. Based on a survey of floodplain and alpine sites in northern Victoria and Tasmania conducted in January-February 1999 we recorded 20 new bdelloid species for Australia. This brings the continental record to 106 species. The description of Philodinavus aussiensis n.sp. is given, with SEM images of its trophi. Trophi of three more bdelloid species are here presented.

There is presently, a substantial amount of information being gathered concerning the environmental risk associated with the perfluorooctanoic acid (PFOA) compound. The aim of this paper was to determine a 35 day community no observable effect concentration (NOECcommunity) or lowest observable effect concentration (LOEC) for freshwater zooplankton exposed to PFOA during a study in 30 1 indoor aquatic microcosms. Some significant (P<0.01) temporal fluctuations in zooplankton abundance were observed, however, a NOECcommunity could not be calculated. LOEC for various species varied between 10 and 70 mg 1-1. According to LOEC values, the tentative order of descriptors sensitivity was as follows: Daphnia magna>richness>=Cyclops canthocamptus staphylinus>Cyclops diaptomus>total zooplankton>=Rotifera sp. The long term ecological significance of these temporal fluctuations could not be determined in this study, however, the overall study cessation analysis showed that the structure of the ecosystem was changed from a more diverse community dominated by larger species towards a less diverse community dominated by smaller more and robust species (P<0.05). Additional chronic toxicity testing should also be addressed since these compounds are so persistent and recalcitrant.

Population growth and life table demography of the predatory rotifer A. girodi using spineless Brachionus calyciflorus and spined Brachionus havanaensis as prey at densities of 1, 2, 4 and 8 ind. ml-1 at 25[degree]C were studied. Regardless of the prey species, the population of A. girodi increased with increasing availability of Brachionus in the medium. At any given prey density, A. girodi fed B. calyciflorus showed consistently better growth than when fed B. havanaensis. The maximum population densities of A. girodi varied from 0.28 to 1.8 ind. ml-1 depending on the prey species and the density. The rate of population increase observed in population growth studies varied from 0.17 to 0.43 day-1 when fed B. calyciflorus and 0.09 to 0.27 day-1 when fed B. havanaensis. Male population of A. girodi was closely related to female density. The lowest average lifespan was observed for A. girodi when fed B. havanaensis at 1 ind. ml-1, while the converse was the case when fed B. calyciflorus at comparable prey concentration. Net reproductive rates varied from 16 to 26 offspring female-1 lifespan-1 depending on the prey species and concentration. Generation time of A. girodi decreased with increasing food concentrations for both the prey species. The rates of population increase obtained from life table demography were lower for A. girodi when fed B. havanaensis than when fed B. calyciflorus.

We studied the population growth of three Brachionus species (B. calyciflorus, B. patulus and B. rubens) using domestic (Mexico City) wastewater at different phases of treatment (treated: type C, partially treated: type B and crude: type A). We also evaluated growth characteristics of a predatory rotifer (Asplanchna sieboldi) fed B. rubens raised on wastewater and compared the growth rates of animals fed cultured algae. All the three tested brachionid species grew well in controls (i.e. fed on the alga Chlorella). However, populations of B. calyciflorus and B. patulus did not grow on the fully treated wastewater (type C). All three brachionid species grew poorly on partially treated wastewater (type B). In crude wastewater, B. rubens reached densities as high as 200 ind. ml(-1). Regardless of Brachionus species, the rates of population increase per day (r) varied between 0.29 and 0.4 in the controls. B. rubens in crude wastewater experienced steep mortality in the first two days but stabilized thereafter. It had generation times, which varied from 3 to 5 days depending on the treatment. Prey (B. rubens) raised on wastewater supported better population growth of A. sieboldi, the highest being from crude wastes. The growth rate of A. sieboldi fed B. rubens, raised on crude wastewater, was the highest (similar to0.8 d(-1)). Thus, the present study showed that culturing of certain species of brachionid rotifers on crude wastewater or partially treated is feasible without addition of alga.

Parthenogenetic lineages within non-marine ostracods can occur either in mixed (with sexual and asexual females) or exclusively asexual taxa. The former mode of reproduction is associated with a high intraspecific diversity at all levels (genetic, morphological, ecological) and, at least in the Cypridoidea, with geographical parthenogenesis. Obligate asexuality is restricted to the Darwinuloidea, the strongest candidate for an ancient asexual animal group after the bdelloid rotifers, and is characterized by low diversity. We have compared rates of molecular evolution for the nuclear ITS1 region and the mitochondrial COI gene amongst the three major lineages of non-marine ostracods with sexual, mixed and asexual reproduction. Absolute rates of molecular evolution are low for both regions in the darwinulids. The slow-down of evolution in ITS1 that has been observed for Darwinula stevensoni (Brady & Robertson) apparently does not occur in other darwinulid species. ITS1 evolves more slowly than COI within non-marine ostracod families, including the darwinulids, but not between superfamilies. The ancient asexuals might have a higher relative substitution rate in ITS1, as would be expected from hypotheses that predict the accumulation of mutations in asexuals. However, the speed-up of ITS could also be ancient, for example through the stochastic loss of most lineages within the superfamily after the Permian-Triassic mass extinction. In this case, the difference in rate would have occurred independently from any effects of asexual reproduction.

Fully asexual lineages cannot purge accumulating mutations from their genome through recombination. In ancient asexuals that have persisted without sex for millions of years, this should lead to high allelic divergences (the 'Meselson effect') as has been shown for bdelloid rotifers. Homogenizing mechanisms can counter this effect, resulting in low genetic diversity within and between individuals. Here, we show that the ancient asexual ostracod species Darwinula stevensoni has very low nucleotide sequence divergence in three nuclear regions. Differences in genetic diversity between embryos and adults furthermore indicate that up to half of the observed genetic changes in adults can be caused by somatic mutations. Likelihood permutation tests confirm the presence of gene conversion in the multi-copy internal transcribed spacer sequence, but reject rare or cryptic forms of sex as a general explanation for the low genetic diversity in D. stevensoni. Other special mechanisms (such as highly efficient DNA repair) might have been selected for in this ancient asexual to overcome the mutational load and Muller's ratchet. In this case, our data support these hypotheses on the prevalence of sex, even if the two extant ancient asexual groups (bdelloids and darwinulids) seem to follow opposite evolutionary strategies.

Epiphanes senta is a littoral rotifer species that occurs in temporary waters and displays a mating behaviour which has not, to my knowledge, so far been described for monogonont rotifers. Monogonont rotifers show distinctive periods within their life cycle during which mictic females appear. Mictic females produce haploid eggs that develop into males or into diapausing eggs if fertilized. The females of E. senta are mostly stationary on the substrate while males are more active swimmers. If they encounter eggs with female embryos of their own species, they attend them and mate with the hatching female. Experiments showed that males are able to discriminate between male, female and diapausing eggs. They exhibit a strong preference for female eggs that are only a few hours away from hatching compared with eggs in early developmental stages. Further experiments did not show any significant differences in male attendance of mictic and amictic eggs. It is hypothesized that males judge the age of a female egg by sensing a chemical that is produced by the growing embryo and diffuses through the egg shell. The male mating behaviour is similar to precopulatory mate guarding known from arthropods but it lacks the monopolization of the female by the male.

Microfaunal diversity in a biodiversity hotspot: new rotifers from southwestern Australia. Zoological Studies 42(4): 516-521. We present the descriptions of 3 new and apparently endemic species of rotifer (Rotifera: Monogononta: Lecanidae, Trichocercidae). Lecane halsei sp. nov. belongs to the L. ludwigii (Eckstein)-group, and is diagnosed by the absence of a posterior projection on the lorica. The taxonomy of the L. ludwigii-group is commented upon, Lecane noobijupi sp. nov. is a sister taxon of the common, cosmopolitan L. bulla (Gosse), whereas Trichocerca wanarra sp. nov. is close to T. insignis (Herrick), T. myersi (Hauer), and T. plaka (Myers), but the trophi are characteristic. The 3 new species illustrate the diversity of the freshwater microfauna in southwestern Australia, and the need for a thorough taxonomic approach to biodiversity inventories of cryptic microfaunal groups.

An analysis of distribution patterns reveals a unique group of Nearctic endemics in Trichocerca Lamarck, 1801. This group, comprising 13.4% of all taxa analysed in the genus, is of diverse origin. A glacial origin is postulated for one species. The observed biogeographic pattern of eight others, and possibly two New World taxa, suggests a pre-Pleistocene origin followed by differential extinctions during glaciations in the Nearctic and Palaearctic. In general, endemism in Trichocerca is strongly biased towards the Northern hemisphere, with no endemism in tropical regions. This suggests a Laurasian origin of the genus. The analysis further reveals a majority (65.7%) of widely distributed taxa, with strict cosmopolitanism in more than a third of the species analysed. Latitudinal variation is evident in 26.9% of Trichocerca, and a warm-water preference appears to be indicated for a majority of these. Although the results should be interpreted with caution due to confused taxonomy, a Southern hemisphere, warm-water and Northern hemisphere, cold water component appear to be present. Comments on the taxonomy and distribution of several species are provided, along with illustrations of poorly known species. Suggestions include elevating T. maior (Hauer, 1936) to species rank, and several new cases of synonymy.

Rotifers present a high diversity in freshwater ecosystems. This study registered 11 genera and 42 species, new records for the Upper Parana River floodplain. These results showed an increase in rotifer diversity in this ecosystem from 184 to 230 species. Among them some were registered only in the rivers and others in the lagoons. Thirty-seven species occurred in the littoral zone and 34 species in the pelagic; 3 species were registered only in the former zone and 2 species only in the latter. The lagoons presented the greatest richness, probably because of the greater stability, low current velocity, and the extensive aquatic macrophyte banks in the littoral zone of these environments as compared to those of the rivers. The highest number of species in the littoral habitats occurred due to the greater influence of shoreline vegetation, which allows greater habitat diversification. This fact contributed to the occurrence of non-planktonic species in the zooplankton samples.

From 20 April to 25 June in 1999, an enclosure experiment was conducted in Lake Donghu to assess the impact of planktivorous silver carp on the planktonic rotifer community. We set up four treatments with silver carp biomass at 0, 116, 176, and 316 g m(-2). Total rotifer density was significantly higher in the no-fish enclosure than in fish-present enclosures. Fish predation on the rotifers alleviated zooplankton competition and resulted in dominance of small zooplankton species (Anureaopsis fissa, Trichocerca pusilla and Moina micrura) in fish-present enclosures. However, some relatively larger species (Polyarthra vulgaris, Brachionus angularis, Brachionus calyciflorus, and Asplanchna spp.) showed higher densities in the no-fish enclosure than in fish-present enclosures.

Replicated groups of Atlantic cod were reared for up to 40 days in 100 l tanks stocked at a density of 75 eggs l(-1). Larvae were transferred from rotifers, Brachionus plicatilis, to either fresh-hatched or enriched Artemia nauplii on each of days 5, 15 and 25 post-hatch (ph). Rotifers were progressively withdrawn over a 5 day period. The type of Artemia offered (fresh-hatched, enriched) did not affect survival or growth rates at any of the 3 transfer ages. Larvae transferred to Artemia from day 5 ph suffered a high incidence of swimbladder over-inflation and high mortality during metamorphosis (<1% survival to day 36 ph). Cod in the day 15 and day 25 transfer groups did not differ significantly in weight-specific growth rate or size on day 40 ph ( mean standard length 13.8 mm, dry weight 3.8 mg). Highest mean survival rates to day 40 ph (18.1%) and lowest mortality following transfer to nursery tanks were also observed in the day 25 transfer groups. Fish that received Artemia from day 5 ph contained circa twice as much total lipid per unit body weight and had a 30% higher triacylglycerol ( TAG) content compared to all other groups. Ratios of the essential fatty acids docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and arachidonic acid (ARA) also differed according to age-at-transition. DHA: EPA ratio exceeded 1 only in cod transferred to Artemia on day 25 ph. Based on these findings, it is recommended that intensively reared Atlantic cod should continue to receive rotifers until completion of metamorphosis.

Rotifers, one of the smallest metazoans, are only seldom found in marine environments. Surprisingly, we discovered high abundances of at least two new species of rotifers settling in anoxic and highly sulphidic sediments associated with shallow gas hydrates (GH) at the southern crest of Hydrate Ridge off Oregon, NE Pacific, in a water depth of about 780 m. At basins adjacent to Hydrate Ridge, 1,285-2,304 m deep, we found rotifers co-occurring with the sulphide-oxidising bacteria Thioploca sp.

The jaws of Limnognathia maerski, Micrognathozoa, were investigated with light- and scanning electron microscopy. The study yielded several new structures and sclerites, including the ventral part of main jaw, the pharyngeal lamellae, the manus, the dorsal and ventral fibularium teeth, and a reinterpretation of the fibularium compartmentalization. Furthermore, it was shown that several jaw elements are composed of densely packed rods. Comparison with Rotifera and Gnathostomulida suggested that the micrognathozoan main jaw is homologous with the rotifer incus and the gnathostomulid articularium and that the pseudophalangids (the ventral jaws) and their associated sclerites correspond to the rotifer mallei. These results imply that Micrognathozoa is more closely related to Rotifera than to Gnathostomulida.

The body-wall and visceral musculature of Notholca acuminata was visualized using phalloidin-linked fluorescent dye under confocal laser scanning microscopy. The body-wall musculature includes dorsal, lateral, and ventral pairs of longitudinally oriented body retractor muscles, two pairs of head retractors, three pairs of incomplete circular muscles, which are modified into dorso-ventral muscles, and a single pair of dorsolateral muscles. The visceral musculature consists of a complex of thick muscles associated with the mastax, as well as several sets of delicate fibers associated with the corona, stomach, gut, and cloaca, including thin longitudinal gut fibers and viscero-cloacal fibers, never before reported in other species of rotifers. The dorsal, lateral, and ventral retractor muscles and the incomplete circular muscles associated with the body wall appear to be apomorphies for the Rotifera. Muscle-revealing staining shows promise for providing additional information on previously unrecognized complexity in rotifer musculature that will be useful in functional morphology and phylogenetic analyses.

1. Larger body size at low temperatures is a commonly observed phenomenon in ectothermic organisms. The mechanisms that lead to this pattern and its possible adaptive significance were studied in laboratory experiments using the parthenogenetically reproducing rotifer Synchaeta pectinata .2. At low temperatures of 4degreesC mean body volume was 46% larger than in individuals cultured at 12degreesC. Egg volume was 35% larger in low vs high temperatures.3. Larger body size at low temperatures was caused by two mechanisms. First, when exposed to low temperatures, mothers laid larger eggs and the hatchlings of these eggs developed into larger adults (irrespective of temperature). Second, individuals cultured at low temperatures grew to a larger body size during their juvenile phase. The former mechanism had a greater influence on adult size than the latter.4. The production of larger eggs at low temperatures seemed to be due to a higher reproductive investment into individual offspring as it occurred independently of differences in maternal size.5. Life table experiments showed that offspring from small eggs (produced at high temperatures) had a significantly higher population growth rate than offspring from large eggs, when cultured at high temperatures. This was mainly due to an increase in fertility during the first days of adult life.

Induction of mixis (sexual reproduction) in rotifers of the genus Brachionus is believed to be triggered by a chemical that is released into the water and accumulates at high population densities. However, direct and conclusive evidence for this hypothesis is thus far lacking. In this study, two mass cultures of the rotifer Brachionus plicatilis were monitored as they grew from low to high population densities. Conditioned water was prepared daily from these cultures, and females were exposed in a bioassay, which consisted of juvenile Brachionus, cultured individually in large volumes that would normally suppress mixis. Conditioned water induced mixis in the bioassay at rates comparable to those found in the mass cultures. Both in bioassay and mass cultures, mixis was essentially absent in the beginning of the experiment, when population densities were very low. The first mictic females appeared at densities of 0.1 females ml-1, and their proportion increased rapidly as the populations grew to >1 female ml-1. The maximum rates of mixis in the bioassay were highly significant and reached 51% of those observed in the mass cultures. These results strongly support the hypothesis that mixis in Brachionus plicatilis is induced by a density-dependent chemical cue.

Predation by free-living protozoa and rotifers was investigated as a possible mechanism for the removal of Cryptosporidium parvum oocysts in aquatic ecosystems including wastewater treatment plants. Free-living ciliated protozoa (Stylonychia mytilus, Paramecium caudatum and an unidentified wastewater wetland ciliate), an amoeba (Acanthamoeba culbertsoni) and rotifers, all commonly found in aquatic ecosystems, were exposed to varying doses of C. parvum oocysts. All organisms investigated ingested oocysts. Predation activity and rates of ingestion varied with predator species and prey density. Ciliated protozoa demonstrated greater predation activity than A. culbertsoni or rotifers when exposed to 2 x 10 super(5) oocyst/mL for up to 3 h. Greatest predation after 1 h exposure was observed in P. caudatum, the largest ciliate, with on average 1.9 oocysts/cell (range 0-9 oocysts/cell). Stylonychia mytilus and the wetland ciliate had a similar mean ingestion of around 0.3 oocysts/cell, with numbers internalised ranging from 0-3 oocysts/cell. Rotifers ingested on average 1.6 oocysts/individual (range 0-7 oocysts/individual) whilst amoebae ingested on average 1.8 oocysts/cell after 2 h exposure (up to 3 oocysts/cell). Grazing activity by P. caudatum was demonstrated at a variety of prey levels ranging from 9 to 9,000 oocysts. Numbers of oocysts internalised by Paramecium frequently exceeded the reported human infective dose of 30 oocysts. In general, numbers of internalised oocysts increased with incubation time of up to 20-30 min although the rate of accumulation was slower at lower dose levels. The significance of predation on the fate of Cryptosporidium oocysts in the environment is discussed.

The taxonomic position of the fluorescent amplified fragment length polymorphism fingerprinting groups A46 (five isolates), A51 (six isolates), A52 (five isolates) and A53 (seven isolates) obtained in a previous study were further analysed through a polyphasic approach. The 23 isolates were phylogenetically related to Vibrio splendidus, but DNA-DNA hybridization experiments proved that they belong to three novel species. Chemotaxonomic and phenotypic analyses further disclosed several features that differentiate between the 23 isolates and known Vibrio species. The names Vibrio kanaloae sp. nov. (type strain LMG 20539T= CAIM 485T; EMBL accession no. AJ316193; G+C content 44-7 mol°/o), Vibrio pomeroyi sp. nov. (type strain LMG 20537T= CAIM 578T; EMBL accession no. AJ491290; G+C content 44-1 mol%)and Vibrio chagasii sp. nov, (type strain LMG 21353T = CAIM 431T; EMBL accession no. AJ316199; G+C content 44-6 mol°/o) are respectively proposed to encompass the five isolates of A46, the six isolates of A51 and the 12 isolates of A52/A53. The three novel species can be distinguished from known Vibrio species by several phenotypic features, including utilization and fermentation of various carbon sources, [beta]-galactosidase activity and fatty acid content (particularly of 12:0, 14:0, 14:0 iso and 16:0 iso).

The fluorescent amplified fragment length polymorphism (FAFLP) groups A5 (21 isolates), A8 (6 isolates) and A23 (3 isolates) distinguished in an earlier paper(Thompson et al., Syst Appl Microbiol 24, 520-538, 2001) were examined in more depth. These three groups were phylogenetically related to Vibrio tubiashii, but DNA-DNA hybridization experiments proved that the three AFLP groups are in fact novel species. Chemotaxonomic and phenotypic analyses further revealed several differences among the 30 isolates and known Vibrio species. It is proposed to accommodate these isolates in three novel species, namely Vibrio neptunius (type strain LMG 20536T; EMBL accession no. AJ316171; G+C content of the type strain 46.0 mol%), Vibrio brasiliensis (type strain LMG 20546T; EMBL accession no. AJ316172; G+C content of the type strain 45.9 mol%) and Vibrio xuii (type strain LMG 21346T; EMBL accession no. AJ316181; G+C content of the type strain 46.6 mol%). These species can be differentiated on the basis of phenotypic features, including fatty acid composition (particularly 14:0 iso, 14:0 iso 3-OH, 16:0 iso, 16:0, 17:0 and 17:1[omega]8c), enzyme activities and utilization and fermentation of various carbon sources.

Physical conditions are usually considered pre-eminent in controlling river plankton, but biotic interactions may be important in slackwater areas. To begin testing this general hypothesis, we conducted a 12-day, predator-prey experiment in 3500 litre mesh enclosures in a slackwater area of the St. Lawrence River using planktivorous, juvenile yellow perch (Perca flavescens) and Dreissena mussels. Results generally supported our hypotheses that: (1) perch would directly suppress large zooplankton via predation but benefit microzooplankton through indirect interactions; and (2) dreissenids would directly depress rotifer densities via predation and have indirect negative effects on macrozooplankton. Based on gut contents of experimental fish, cladocera were the principal prey of smaller yellow perch (c. 46-50 mm), followed by copepods, ostracods, and rotifers. Larger juvenile perch (c. 67-73 mm) fed almost exclusively on copepods and ostracods. Densities of calanoid copepodids, nauplii, and some cyclopoid copepods (Diacyclops thomasi) were significantly depressed by perch, and adult Eurytemora affinis (99% of adult calanoids) essentially disappeared from fish enclosures. Despite being a favourite prey item of small perch, densities of the small cladoceran Bosmina (Sinobosmina) spp. were significantly higher when fish were present (150% greater than control densities on Day 12). Densities of the very abundant rotifer Polyarthra were >300% greater in fish enclosures than controls by Day 12, and the rotifers Synchaeta and predaceous Ploesoma were significantly more abundant in the presence of perch. Increases in rotifers and cladocera suggest indirect, positive effects of fish related to significantly higher phytoplankton biomass or decreased densities of predaceous copepods. Densities of eight of ten zooplankton groups examined declined significantly when mussels were present, and calanoid copepodids also declined but not significantly. Chlorophyll-a concentrations were slightly lower in mussel enclosures. This evidence suggests biotic interactions play important roles among potamoplankton in slackwater habitats, but river-wide implications of these findings require further study.

In 1702, Van Leeuwenhoek was the first to describe the phenomenon of anhydrobiosis in a species of bdelloid rotifer, Philodina roseola. It is the purpose of this review to examine what has been learned since then about the extreme desiccation tolerance in rotifers and how this compares with our understanding of anhydrobiosis in other organisms. Remarkably, much of what is known today about the requirements for successful anhydrobiosis, and the degree of biostability conferred by the dry state, was already determined in principle by the time of Spallanzani in the late 18th century. Most modern research on anhydrobiosis has emphasized the importance of the non-reducing disaccharides trehalose and sucrose, one or other sugar being present at high concentrations during desiccation of anhydrobiotic nematodes, brine shrimp cysts, bakers' yeast, resurrection plants and plant seeds. These sugars are proposed to act as water replacement molecules, and as thermodynamic and kinetic stabilizers of biomolecules and membranes. In apparent contradiction of the prevailing models, recent experiments from our laboratory show that bdelloid rotifers undergo anhydrobiosis without producing trehalose or any analogous molecule. This has prompted us to critically re-examine the association of disaccharides with anhydrobiosis in the literature. Surprisingly, current hypotheses are based almost entirely on in vitro data: there is very limited information which is more than simply correlative in the literature on living systems. In many species, disaccharide accumulation occurs at approximately the same time as desiccation tolerance is acquired. However, several studies indicate that these sugars are not sufficient for anhydrobiosis; furthermore, there is no conclusive evidence, through mutagenesis or functional knockout experiments, for example, that sugars are necessary for anhydrobiosis. Indeed, some plant seeds and micro-organisms, like the rotifer, exhibit excellent desiccation tolerance in the absence of high intracellular sugar concentrations. Accordingly, it seems appropriate to call for a re-evaluation of our understanding of anhydrobiosis and to embark on new experimental programmes to determine the key molecular mechanisms involved.

Zooplankton surveys were made from May, 1997, to July, 2000, in the detention pond closed off from Isahaya Bay, an inlet of Ariake Sound, to follow changes in the zooplankton community concomitant with desalination after the closing of the dike in April, 1997. Mean salinity at the surface decreased from 27 to 3.9 psu in the four months after closing. Mean density of zooplankton (excluding protozoans) increased from 11.7 l-1 in May, 1997, to 225.7 l-1 in August, 1997, mainly due to increases in copepod nauplii and the rotifers Brachionus plicatilis and probably B. rotundiforms. Copepods consisted mostly of Oithona davisae (86%) and Acartia pacifica (10%) in May, 1997, but these had been completely replaced by brackish-water species, Sinocalanus tenellus (44%), Pseudodiaptomus inopinus (35%), and Paracyclopina nana (19%) by August, 1997. With further desalination, the proportion of freshwater copepods, consisting mostly of Thermocyclops spp., increased. Zooplankton densities in the pond were comparable to those in other brackish waters until one year after closing. However, densities in the summers of 1998 and 1999 were significantly lower (<10 l-1) than in 1997 and 2000; food-limitation and the extremely low salinities (<1.0 psu) are discussed as possible causes of the low densities in 1998 and 1999. Occurrences of marine copepods and the appendicularian Oikopleura sp. in 2000 suggest inflow of seawater through the gates of the dike.

A total number of 1473 Vibrio isolates were collected from different aquaculture systems in many countries. Isolates were obtained from bivalves (mussels, scallops, oysters), shrimp and fish, sea urchins, live feed (algae, Artemia, rotifers), seaweed, aquaculture market products and from the aquaculture environment (tank water, seawater, sediments). Eggs, healthy and diseased or dead larvae, and adult organisms were sampled from cold-water species and moderate- to warm-water species. All isolates were phenotypically characterized using the Biolog GN technique. Eighty-nine different clusters were obtained, of these clusters, only 33 were identified comprehending 992 isolates. The remaining 56 groups did not cluster with any of the included type strains and remained unidentified. Seventy-eight isolates did not cluster with any other strain. It was shown that the Vibrio genus is a phenotypically diverse group making the identification with the Biolog system difficult and unreliable.

This paper evaluates long-term changes in the atmospheric depositions of S and N compounds, lake water quality, and biodiversity at eight glacial lakes in the Bohemian Forest over the past 130 years. This time interval covers 0) the 'background' pre-acidification status of the lakes, (ii) a period of changes in the communities that can be partly explained by introduction of fish, (iii) a period of strong lake acidification with its adverse impacts on the communities, (iv) the. lake reversal from acidity, which includes the recent status of the lakes. The lake water chemistry has followed-with a characteristic hysteresis-both the sharp increase and decline in the deposition trends of strong anions. Remarkable changes in biota have mirrored the changing water quality. Fish became extinct and most species of zooplankton (Crustacea) and benthos (Ephemeroptera and Plecoptera) retreated due to the lake water acidification. Independent of ongoing chemical reversal, microorganisms remain dominant in the recent plankton biomass as well as in controlling the pelagic food webs. The first signs of the forthcoming biological recovery have already been evidenced in some lakes, such as the population of Ceriodaphnia quadrangula (Cladocera) returning into the pelagial of one lake or the increase in both phytoplankton biomass and rotifer numbers in another lake. (C) 2002 Elsevier Science B.V. All rights reserved.

Pelagic rotifers were studied in lakes with contrasting acidification histories situated in an acid-stressed region of southern Norway. Life histories and spatial distribution varied considerably between the investigated species, and influenced the recovery processes. Most headwater lakes have experienced strongly acidified environments during the last five decades, whereas lakes close to the Skagerrak coast have been stable within the same period. Rotifer diversity and abundance were reduced in the most acidic sites and increased towards the coast. Most surveyed species are known to possess sediment egg-banks, and after chemical recovery most rotifers dispersed into the plankton from these egg-banks and produced viable populations. Some species of the genera Polyarthra and Collotheca, and the species Kellicotta longispina and Keratella serrulata showed a striking ability to tolerate acidification, and were the dominant taxa in the acidmost environments. K. serrulata characterised, but did not numerically dominate, acid rotifer communities especially in the most coloured sites, and decreased following liming. The predominantly bacteriophageous genus Conochilus exploded in numbers shortly after liming, most probably because bacteria increased strongly during this transition phase. Planktivorous fish influenced indirectly rotifer abundance by consuming invertebrate predators and important rotifer competitors such as filter feeding cladocerans. Invertebrate predators, such as larvae of Chaoborus spp. and Heterocope saliens probably influenced rotifer distributional patterns in a complex top- down manner, both during chronic acidification and liming in environments with low fish predation. Important rotifer predators such as pelagic cyclopoid copepods, Bythotrephes longimanus and Leptodora kindti, were absent from the most acidic fishless lakes. Considerable populations of large-sized Daphnia longispina probably suppressed several rotifer species in sites with low fish predation, as did large populations of Bosmina longispina and Ceriodaphina quadrangula in lakes with intense fish predation.

The approximately 360 species of the Class Bdelloidea (Phylum Rotifera) constitute the largest, most diverse and oldest eukaryotic group for which obligate asexuality has morphological, cytological and molecular support. DNA sequence studies indicate that the class constitutes a single clonal lineage, 50-100 million years old. Here we report cytofluorometric measurements of oocyte nuclear DNA content and GC proportion for six bdelloid species, representing the three major families of Bdelloidea. We find wide differences between species in nuclear DNA content (0.5-2.4 pg) and proportion of GC (37-57%). The proportion of GC in the nuclear DNA of all six species is greater than that in their coding regions examined to date, and tends to be greater in species with greater nuclear DNA content. Interspecific differences in nuclear DNA content do not correlate with chromosome numbers, which range from 10 to 13, and are therefore not due to differences in ploidy. In addition, since bdelloids seemingly lack functional reverse transcriptase genes, the observed interspecific differences in nuclear DNA content and GC proportion do not appear to have resulted from retrotransposon activity. The values of oocyte nuclear DNA content obtained by cytofluorometric measurement are close to the values of total genome size we previously obtained from measurements of DNA hybridization intensity, indicating that bdelloid genomes do not undergo significant somatic chromatin diminution and, unlike the genomes of sexually reproducing diploids or polyploids, do not consist of two or more nearly identical haplotypes.

The effects of cypermethrin, a commonly used pyrethroid insecticide, were studied in small in situ enclosures situated in an eutrophic lake over an 11-day period. The experimental design used a regression principle that included three untreated controls and a gradient of six unreplicated cypermethrin concentrations, ranging from 0.01 to 6 mu g/l. This paper is the second in a series of two and describes the effects on the species composition of the crustacean, rotifer, periphyton and phytoplankton communities. Multivariate ordination technique (redundancy analysis (RDA) combined with Monte Carlo permutation tests) showed that exposure to cypermethrin caused significant changes in the species composition of the communities. Changes in the structure of the communities were observed following exposure to a nominal concentration of 0.13 mu g cypermethrin per litre above. The direct acute effect of exposure to cypermethrin was a rapid decrease of many species of crustacean zooplankton. The alterations in crustacean species composition were probably due to variations in susceptibility to the direct toxic effects of cypermethrin. No effects concentration (NEC) for individual zooplankton species were calculated using inverse regression and revealed that copepod nauplii were the most sensitive (NEC=0.01 mu g/l) of the crustacean groups examined. The observed alterations of the species composition of the autotrophic communities as well as of the rotifers were most likely caused indirectly by cypermethrin, mediated through the direct negative effects of the insecticide on the crustacean grazers. The results of this experiment provide further knowledge about the direct and indirect effects of pesticide stress on the ecosystem level. They also show that there is a variation in sensitivity between different species of zooplankton under natural conditions and thus exemplify the necessity of multispecies approaches in the risk assessment of pesticides.

We tested the hypothesis that mesozooplankton is a potential food source for 2 marine mussels; the temperate blue mussel Mytilus edulis and the tropical and subtropical green mussel Perna viridis. We fed the rotifer Brachionus plicatilis to each mussel species at 3 rotifer densities (0.1, 0.5, and 1.0 ind./ml) and found that each mussel species could significantly reduce the abundance of rotifers. We also labeled rotifers by feeding them super(14)C-labeled phytoplankton. The labeled rotifers were fed to mussels at densities of 0.1, 0.2, 0.5, and 1.0 individuals ml-1, and the assimilation efficiencies were generally higher at higher rotifer densities (59 to 73% for M. edulis and 37 to 73% for P. viridis). After standardization for mass and metabolic requirements, we calculated that rotifers make significant contributions to the mussels' energy budgets, which provides quantitative evidence for a potential trophic link between mesozooplankton and marine benthic bivalves. This study demonstrates that mesozooplankton could have an important role in the transformation of energy between benthic and pelagic systems in coastal areas. Dense populations of bivalves could exert a strong top-down effect on planktonic food webs.

Soil microfauna in 0- to 10-cm soil under grazed pasture on a sand (Mollic Psammaquent) was assessed quarterly in free air CO2 enrichment (FACE) rings that were at either ambient CO2 or had been exposed to 475 mul 1(-1) CO2 for 4-5 years. There were significant increases in nematode (1.5x) and rotifer (4. 1 x) abundance in soils subjected to elevated CO2. Ten nematode taxa were significantly more abundant under elevated CO2. The greatest increase was 4.3x in root-feeding Longidorus. three other root-feeders showed no increase in population densities at elevated CO2. Bacterial-feeding Cervidellus was the only nematode with a significant decrease (0.4x). The abundance of all nematode feeding groups increased significantly in soils subjected to elevated CO). The relative increases in abundance of feeding groups (bacterial-feeders 1.3x, root-feeders 1.3x, plant-associated 1.5x, fungal-feeders 1.6x, omnivores 2.0x, predators 2. 1 x) suggest marked increases in fluxes through microbial-feeding nematodes and a multitrophic response among the soil biota to the increase in atmospheric CO, above ambient. Data from the site suggest soil microbial biomass C and N pools were unchanged over the sampling period. Of eight nematode indices only total maturity index increased (2.9 to 3.2), reflecting the increased proportion of the large Longidorus. Further work on microbial-microfaunal interactions and their micro-scale relation to roots is needed to better understand the impact of increasing atmospheric CO2 on soil processes.

Ecological and evolutionary dynamics can occur on similar timescales. However, theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions. Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey (rotifer-algal) cycles in laboratory microcosms. Our experiments tested explicit predictions from a model for our system that allows prey evolution. We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption, and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population. Single-clone algal cultures (lacking genetic variability) produced short cycle periods and typical quarter-period phase lags between prey and predator densities, whereas multi-clonal (genetically variable) algal cultures produced long cycles with prey and predator densities nearly out of phase, exactly as predicted. These results confirm that prey evolution can substantially alter predator-prey dynamics, and therefore that attempts to understand population oscillations in nature cannot neglect potential effects from ongoing rapid evolution.

Predation and food supply are generally perceived as important determinants of spatial and temporal variations of populations. The population dynamics of freshwater rotifers have been well researched in this aspect. However, their spatial variations have attracted less attention and have not been studied by simultaneously considering both predation and food supply. We studied spatial variations of rotifer abundance among 34 Canadian boreal lakes. A large part of the variance of rotifer abundance was associated with variables related to trophic status including chlorophyll a and total phosphorus. However, abundances of mesozooplankton such as potential predators and competitors did not correlate with rotifer abundance and did not explain the residual of the regression between rotifer abundance and chlorophyll a. The results of the present study indicated that variation in rotifer abundance among lakes was caused by 'bottom-up' forces related to food supply and not by 'top-down' predatory interactions. This provides a contrast to previous empiric and experimental studies that reported that temporal variations of rotifer abundance were mainly regulated by 'top-down' interactions. This discrepancy suggests that overall differences in rotifer abundance among lakes are mainly determined by 'bottom-up' forces while temporal changes in single lakes are shaped by 'top-down' forces. Meanwhile, the composition of rotifer species was correlated with mesozooplankton abundance as well as trophic status. Rotifer species with long spines or rigid loricae were found in the lakes where mesozooplankton were abundant, which suggests that defensive morphology could have affected the rotifer species distribution among the study lakes.

To examine the life history response and age-specific tolerance to starvation in the rotifer Brachionus plicatilis O.F. Muller, we carried out two series of individual culture experiments. In the first experiment, rotifers were fed until each of the ages of 1-4 days, and were then starved during the rest of their lifetimes. The control group was fed throughout their lifespans. Rotifers stopped active reproduction just after the onset of food deprivation, and showed shorter subsequent survival times when they were starved at older ages. The finding that the larger the number of offspring produced before food deprivation, the shorter the subsequent lifetime under starvation, appeared to reflect a trade-off with the cost of reproduction. In the second experiment, newborns were starved until each of the ages of 1-5 days, and were fed thereafter. The lifespans of the rotifers starved up to the age of 3 days were not statistically different from those that were not starved. Although the starved rotifers began to reproduce once fed again, their lifetime fecundity decreased significantly from that of the non-starved group. Based on these results, it was suggested that the reproductive suppression caused by starvation would cause rotifers to have a longer lifespan to allow for future reproduction.

The rotifer Brachionus plicatilis is a widely-used model for population dynamics studies. During the population growth of B. plicatilis, life history parameters such as reproduction and lifespan change widely, and determine the balance between birth and death rates that regulates the population fluctuations. The lifespan of B. plicatilis was extended 30% by inhibiting a phosphatidylinositol-3-OH kinase involved in an insulin/insulin-like growth factor (IGF) signal transduction pathway that regulates the reproduction and lifespan in nematodes. Subsequently, we cloned a cDNA encoding Mn-superoxide dismutase (SOD), which may function downstream of the IGF pathway Real-time reverse-transcription polymerase chain reaction analysis revealed that the expression level of Mn-SOD mRNA was higher in B. plicatilis with longer lifespans than those with shorter lifespans. In addition, stress proteins may also influence population dynamics as molecules regulating lifespan and molecular chaperones to maintain the cellular integrity. Accordingly, we cloned two stress protein genes encoding HSP70 and GRP94, and found that their expression changed during the population growth of rotifers. Thus, this novel approach of integrating population ecology and molecular biology has potential use in investigation the detailed mechanisms of rotifer population dynamics. (C) 2003 Elsevier Inc. All rights reserved.