Daphnia Longispina Research Articles

Temporal changes in cladoceran assemblages subjected to a low calcium environment: combining the sediment record with long-term monitoring data

Lakewater calcium (Ca) decline affects softwater lakes across the Canadian Shield. Ca decline is one consequence of acid deposition, and has impeded biological recovery in formerly acidified lakes. Reduced Ca availability may advantage taxa better adapted to low Ca waters. Crosson Lake in south-central Ontario (Canada) has an extensive monitoring record and has experienced strong Ca decline since the late 1970s, recently falling below 1.5 mg L−1, a threshold value for some large Daphnia O.F. Muller, 1785 taxa. Paleolimnological analysis of the sedimentary cladoceran assemblages revealed that changes associated with the Ca decline began in the early 1970s. Relative abundances of the jelly-clad Holopedium glacialis Rowe, 2007 and the Daphnia pulex complex increased while Ca-sensitive members of the Daphnia longispina complex decreased. Zooplankton net hauls (1981–2010) corroborate the paleolimnological analysis, revealing that increases in the D. pulex complex were due to Daphnia catawba Coker, 1926 (a taxon tolerant of low Ca). Lakewater Ca, dissolved organic carbon and total phosphorus explain a significant amount of variation within the cladoceran community; however, the relationship between Ca concentration and the daphniid community was most apparent. The Crosson Lake paleolimnological and direct monitoring data may describe ecological changes that are also occurring in many other softwater lakes across the Canadian Shield and elsewhere.

Parental and hybrid Daphnia from the D.longispina complex: long-term dynamics in genetic structure and significance of overwintering modes.

In recent decades, hybridization has become a focus of attention because of its role in evolutionary processes. However, little is known about changes in genetic structure within and between parental species and hybrids over time. Here, we studied processes of genetic change in parental species and hybrids from the Daphnia longispina complex (Crustacea, Cladocera) over a period of six years across ten habitats. These cyclical parthenogens respond to fluctuating environments by switching from asexual to sexual reproduction. Importantly, sexually produced diapausing eggs, which resist extreme conditions such as low temperatures and serve as dispersal stages, are produced to a lower extent by hybrids. Long-term microsatellite data revealed clear differences between hybrids and parental species. In hybrids, clonal diversity values were lower, whereas heterozygosity and linkage disequilibrium values were higher compared to parental species. Clonal diversity of hybrids responded to the strength of the winter, with cold winters resulting in few genotypes in the following spring. In time windows when only asexual hybrid females survive, priority effects will favour the establishment of the hybrid offspring before hatchlings from parental diapause eggs can enter the community. The constant high levels of heterozygosity maintained by clonal reproduction in hybrids might lead to their successful establishment over time, when they are able to escape competition from both parental species. Although we found evidence that hybrids diversity depends on fluctuating environments, a direct link between hybrid abundance and the strength of winter was missing. Because of reduced adaptability in clonally reproducing hybrids, multiple factors must contribute to promoting their long-term success in fluctuating environments.

The impact of trout introductions on macro- and micro-invertebrate communities of fishless boreal lakes

Effects of fish introductions on lake ecosystems have long been debated. It has been hypothesized that such effects should be strongest in oligotrophic lakes, where fish were not originally present. We investigated two lakes (one naturally fishless, one fish-stocked in 1980) in northern Fennoscandia, selected because of the absence of other anthropogenic stressors and a well-known stocking history. The diet of the introduced brown trout (Salmo trutta L.) was analysed to estimate the effect of their predation on the pelagic invertebrate communities. Quantitative and qualitative samples were taken to assess the current abundances of pelagic macro- and micro-invertebrates in different habitats of both lakes, to infer the impact of brown trout presence. Past abundances of Cladocera, Chironomidae, Gammarus lacustris and Daphnia longispina were also estimated based on subfossil remains in the sediment, and used to assess how brown trout introduction affected macro- and micro-invertebrates living in different habitats. Relative abundance and species richness of Cladocera were evaluated in sediment cores from both lakes, to assess whether changes were caused by fish-introduction-induced trophic cascades or climate change. Also, planktonic Cladocera (Eubosmina) body sizes were measured to evaluate their response to the release of macro-invertebrate predation pressure. Brown trout introduction displaced macro-invertebrates, i.e. G. lacustris, from the pelagic area, and caused a trophic cascade effect that slightly increased the species richness of Cladocera, but markedly increased their abundance, as shown in the sediment record. Introduced brown trout did not, however, cause a decline in Chironomidae, G. lacustris or D. longispina abundances. On the contrary, it resulted in an approximately five-fold increase in Chironomidae accumulation rates in the sediment. The release of macro-invertebrate predation pressure did not lead to changes in the body shapes of Eubosmina, which could be a consequence of the composition of the original macro-invertebrate species assemblage.

Clonal structure and depth selection during a Caullerya mesnili epidemic in a hybridizing population of the Daphnia longispina complex

Daphnia perform diel vertical migration (DVM), a predator-avoidance strategy to migrate towards deeper and colder layers in the water column in the morning and movement to the algae-rich surface layers in the evening. However, individuals performing DVM incur several trade-offs since they might suffer from resource limitation and a slower instantaneous birth rate in deeper depths. DVM patterns may be modified by abiotic factors such as temperature, food concentration, or pH and vary among different Daphnia species and genotypes. Furthermore, Daphnia host a variety of microparasites that might pose an additional factor influencing DVM behaviour. For infected individuals, migration into cooler temperature layers might slow down parasite growth. Moreover, parasites can increase opacity of their hosts. Non-migrating individuals might then be selectively purged from the upper layers by visually hunting predators. With these premises we asked, whether epidemics of the ichthyosporean parasite Caullerya mesnili affect or are affected by the DVM behaviour of Daphnia in Lake Greifensee, Switzerland by analysing the vertical distribution of Daphnia during day and night on two dates. Furthermore, we were interested whether a potential interaction depends on host genotype. We therefore studied the genotypic composition of the integrated population in regular sampling intervals over the course of one year and on a fine-grained vertical resolution during the Caullerya epidemic in late summer. Since Caullerya-infected Daphnia migrated equally well as uninfected ones, the findings of this study suggest that Caullerya epidemics neither affected nor were affected by the DVM behaviour of Daphnia. We observed clonal succession in the lake but could not link this succession to the Caullerya epidemic; all except one of the common multilocus genotypes were under-infected. In addition, outbreak and course of this Caullerya epidemic seemed to rely mainly on environmental cues. Because this first study only provides a snapshot of time, we hope that further studies will be done to verify our results.

Emergent effects of structural complexity and temperature on predator–prey interactions

AbstractEphemeral aquatic environments are important habitats for a variety of species. They are highly variable with regards to vegetation structure and physico‐chemical features that potentially mediate outcomes of biotic interactions. Multiple environmental variables and their emergent impacts on the relationship between prey consumption rate by a predator and prey density (functional response), however, are rarely assessed. Here, we investigated the combined effects of temperature and habitat complexity on the functional response of the freshwater predatory notonectidEnithares sobriaon the cladoceran prey organismDaphnia longispina. A TypeIIfunctional response was observed forE. sobriapredating onD. longispinaand while temperature and habitat complexity had no effect on the response type, these environmental variables interacted with consequences for the magnitude of the functional responses. Overall, structural complexity favored the predator as greater consumption was observed in the most complex habitat treatment. Temperature effects were also evident although these effects were not unidirectional with regard to treatment factor gradients as predators were the most successful at intermediary temperatures. Furthermore, there was a complex interplay between habitat complexity and temperature, with attack rates being greatest at low and high complexities within intermediate temperatures, while at zero complexity attack rates were greatest at the lowest temperature. The effect of habitat on handling times was only evident in the low temperature treatments which decreased steadily with each increase in complexity. Through the application of functional responses the synergistic effects of multiple environmental drivers on predator–prey interaction outcomes have been highlighted, adding insight into how interactions among species may be affected by natural or artificially induced environmental variability.

Local human pressures influence gene flow in a hybridizing Daphnia species complex.

Anthropogenic environmental changes are considered critical drivers of the genetic structure of populations and communities through, for example, the facilitation of introgressive hybridization between syntopic species. However, the mechanisms by which environmental perturbations trigger changes in the genetic structure of populations and communities, such as the processes that determine the directionality of hybridization and patterns of mitochondrial introgression over many generations, remain largely unexplored. In this study, the changes in genetic structure of hybridizing members of the Daphnia longispina species complex were reconstructed over the last 100 years for three large temperate lakes under strong anthropogenic pressures via palaeogenetic analyses of resting egg banks. Drastic changes in the genetic structure of the Daphnia community, associated with hybridization events between D. longispina and D. galeata and subsequent introgression, were detected in Lakes Geneva and Bourget. In Lake Bourget, these changes were induced by the successful establishment of D. galeata with rising phosphorus levels and reinforced by the sensitivity of D. longispina to fish predation pressure. In Lake Geneva, the pattern of hybridization during eutrophication is more likely a function of the original taxonomic composition of the species complex in this lake. Lakes seem to require at least a meso-oligotrophic status to allow D. galeata populations to establish and accordingly no D. galeata genotypes were found in the egg bank of oligotrophic Lake Annecy. In contrast to the generally assumed pattern of unidirectional hybridization in this species complex, bidirectional hybridization was recorded in Lakes Geneva and Bourget. Our results also demonstrate complex genetic trajectories within this species complex and highlight the irreversibility of changes in the genotypic architecture of populations driven by local human pressures. Finally, we show that extensive hybridization and introgression do not necessarily result in a large and homogenous hybrid swarm.

ZOOPLANKTON OF KILAVUZLU DAM LAKE (KAHRAMANMARAŞ) AND THE EFFECT OF CAGE FISH FARMING ON WATER QUALITY AND ZOOPLANKTON FAUNA OF THE DAM LAKE

Water quality parameters and zooplankton fauna of Kilavuzlu Dam Lake were determined. It was found that among water quality parameters, sechi depth, temperature, silica, Ca and CaCO 3 amounts were higher in the first (referans) station; while conductivity, dissolved oxygen, pH, chlorophyll a , nitrate and phosphate values were higher in second (cage) station. A total of 57 taxa were identified in the study. Of these taxa, 33 belonged to Rotifera, 14 belonged to Cladocera and 10 belonged to Copepoda. It was found that Keratella cochlearis , Daphnia longispina , Cyclops vicinus , Acanthodiaptomus denticornis were the most common throughout the year, while Ascomorpha ovalis , Dicranophorus epicharis , Keratella tecta , Notholca acuminata , Testudinella patina , T. mucronata , Trichotria pocillum , Disparalona rostrata , Scapholeberis kingi , Leydigia leydigi , Alona guttata , Eucyclops speratus , Paracyclops chiltoni were the least species. Monommata longiseta , Trichocerca porcellus , Diaphanasoma birgei , Eurycercus lamellatus were only found in the first station, while Ascomorpha ovalis , Notholca acuminata , Rotaria neptunia , Trichotria pocillum , Disparalona rostrata and Eucyclops speratus were only found in the second station. Rotifera was represented with higher number of species in first station for 5 months but Copepoda was represented with higher number of species in second station for 5 months. The abundance of groups according to months and stations revealed that Rotifera and Copepoda were abundant quantitatively in first station for 7 months; while Cladocera was abundant in first station for 8 months. On the other hand, amount of all zooplankton species were found to be more abundant in cage station in April (6605 ±4597.35 individual m -3 ) and more abundant in first station in September (1635 ±2384.852 individual m -3 ) (P > 0.05).

Feasibility of planctomycetes as a nutritional or supplementary food source forDaphniaspp

Daphnia magna is widely used as a standard organism in ecotoxicology assays. It plays a key role in energy transfer in freshwater food webs as a primary consumer, grazing on microalgae, yeast and bacteria. Daphnids are commonly reared in the laboratory using microalgae cultures but alternative or complementary sources are important to reduce the dependency on a single food source. The role played in nature by planctomycetes as a food source for other higher trophic levels is still unknown. In this study, we aimed to evaluate the potential of Rhodopirellula rubra strain LF2 as a nutritional or a supplementary food source for D. magna and Daphnia longispina . Life-history assays were conducted with daphnids fed with R. rubra in exponential and stationary growth phases, in three concentrations. Additionally, its adequacy as a supplement to the microalga Raphidocelis subcapitata was tested. In general, both daphnids showed impairment in all the parameters evaluated, especially when fed with R. rubra . However, when daphnids were fed with the two food sources, no changes were recorded for the rate of population increase. At the tested concentrations, R. rubra was not a good alternative food source in the daphnid diet.

Long-Term Patterns in the Population Dynamics of Daphnia longispina, Leptodora kindtii and Cyanobacteria in a Shallow Reservoir: A Self-Organising Map (SOM) Approach.

The recognition of long-term patterns in the seasonal dynamics of Daphnia longispina, Leptodora kindtii and cyanobacteria is dependent upon their interactions, the water temperature and the hydrological conditions, which were all investigated between 1999 and 2008 in the lowland Sulejow Reservoir. The biomass of cyanobacteria, densities of D. longispina and L. kindtii, concentration of chlorophyll a and water temperature were assessed weekly from April to October at three sampling stations along the longitudinal reservoir axis. The retention time was calculated using data on the actual water inflow and reservoir volume. A self-organising map (SOM) was used due to high interannual variability in the studied parameters and their often non-linear relationships. Classification of the SOM output neurons into three clusters that grouped the sampling terms with similar biotic states allowed identification of the crucial abiotic factors responsible for the seasonal sequence of events: cluster CL-ExSp (extreme/spring) corresponded to hydrologically unstable cold periods (mostly spring) with extreme values and highly variable abiotic factors, which made abiotic control of the biota dominant; cluster CL-StSm (stable/summer) was associated with ordinary late spring and summer and was characterised by stable non-extreme abiotic conditions, which made biotic interactions more important; and the cluster CL-ExSm (extreme/summer), was associated with late spring/summer and characterised by thermal or hydrological extremes, which weakened the role of biotic factors. The significance of the differences between the SOM sub-clusters was verified by Kruskal-Wallis and post-hoc Dunn tests. The importance of the temperature and hydrological regimes as the key plankton-regulating factors in the dam reservoir, as shown by the SOM, was confirmed by the results of canonical correlation analyses (CCA) of each cluster. The demonstrated significance of hydrology in seasonal plankton dynamics complements the widely accepted pattern proposed by the plankton succession model for lakes, the PEG (Plankton Ecology Group), and may be useful for the formulation of management decisions in dam reservoirs.

Is bigger better? A possibility for adaptation of Daphnia to filamentous cyanobacteria in the face of global warming

Body size is a key determinant of fitness in Daphnia. Bigger size means higher feeding efficiency and reproduction. However, filamentous cyanobacteria have a more detrimental effect on larger daphnids. Predicted global warming is expected to reduce size of Daphnia and facilitate frequent occurrence of cyanobacteria. Therefore, we asked two questions: (i) does elevated temperature cause reduced size of daphnids, and (ii) is temperature-dependent size reduction adaptive in an environment dominated by filamentous cyanobacteria? To address these issues, we obtained 8 clones of the Daphnia longispina complex from artificially heated lakes and 8 clones from control lakes, and exposed them to a favorable food Scenedesmus obliquus and a mixture of S. obliquus and the filamentous cyanobacterium Cylindrospermopsis raciborskii in life table experiments at 16, 20, and 24°C. Individuals from heated lakes attained larger body size than those from control lakes. Moreover, exposure to the filamentous cyanobacterium led to reduced fecundity of Daphnia from the non-heated lakes and did not affect reproduction of Daphnia from the heated lakes. We conclude that Daphnia display some evolutionary adaptations to cope with filamentous cyanobacteria, linked to long-term exposition to elevated temperature. Our results violate broadly accepted assumptions that ectotherms are smaller in warmer environments.

How perceived predation risk shapes patterns of aging in water fleas

Predation is an important selection pressure which shapes aging patterns in natural populations, and it is also a significant factor in the life history decisions of individuals. Exposure to the perceived threat of size-dependent fish predation has been shown to trigger adaptive responses in animal life history including an increase in early reproductive output. In water fleas, this response to perceived predation risk appears to have a cost, as a lifespan in an environment free of predation cues is 20% longer. The aim of this study is to establish the biodemographic basis of phenotypic differences in the water flea lifespan which are induced by the cues of fish predation. We examined mortality by fitting the Gompertz–Makeham model of mortality to large cohorts of two cladoceran species, Daphnia longispina and Diaphanosoma brachyurum. Our findings indicate that perceived exposure to the threat of fish predation (induced through chemical cues) only accelerated the rate of aging in Diaphanosoma, and not in Daphnia where the treatment led to an earlier onset of aging. The second of these two phenotypic responses is consistent with the genetically based differences between Daphnia from habitats that differ with respect to predation risk. In contrast, the response of Diaphanosoma demonstrates that the cue of extrinsic mortality—in this case, fish predation—is a key factor in shaping these cladoceran life histories in the wild, and is one of the few interventions which has been shown to induce a plastic change in the rate of aging.

New possibilities arise for studies of hybridization: SNP-based markers for the multi-species Daphnia longispina complex derived from transcriptome data

In order to trace community dynamics and reticulate evolution in hybrid species complexes, long-term comparative studies of natural populations are necessary. Such studies require the development of tools for fine-scale genetic analyses. In the present study, we developed species-diagnostic SNP-based markers for hybridizing freshwater crustaceans: the multispecies Daphnia longispina complex. Specifically, we took advantage of transcriptome data from a key species of this hybrid complex, the annotated genome of a related Daphnia species and well-defined reference genotypes from three parental species. Altogether eleven nuclear loci with several species-specific SNP sites were identified in sequence alignments of these reference genotypes from three parental species and their interspecific hybrids. A PCR-RFLP assay was developed for cost-efficient large population screening by SNP-based genotyping. Taxon assignment by RFLP patterns was nearly perfectly concordant with microsatellite genotyping across several screened populations from Europe. Finally, we were able to amplify two short regions of these loci in formaldehyde-preserved samples dating back to the year 1960. The species-specific SNP-based markers developed here provide valuable tools to study hybridization over time, including the long-term impact of various environmental factors on hybridization and biodiversity changes. SNP-based genotyping will finally allow eco-evolutionary dynamics to be revealed at different time scales.

Biochemical and populational responses of an aquatic bioindicator species, Daphnia longispina, to a commercial formulation of a herbicide (Primextra® Gold TZ) and its active ingredient (S-metolachlor)

The growing demand of human populations for food supplies has led to an increase in the use of synthetic products, mainly pesticides, which induce adverse effects not only to target organisms, but also to non-target biota of agroecosystems. Aquatic ecosystems in the proximity of agricultural areas are particularly vulnerable to pesticides, which cause underperformance or extinction of non-target sensitive species. Once in the aquatic system, these chemicals can affect biological processes at multiple levels (molecular, individual, populational), causing ecosystem imbalance across multiple scales. In this study, the effect of a commercial formulation of a herbicide (Primextra® Gold TZ) and its main active ingredient (a.i., S-metolachlor) was studied on a freshwater cladoceran species (Daphnia longispina), at different levels of biological organization and temporal scales. S-metolachlor is used in many herbicide formulations applied in corn/maize cultures, which is a relevant culture worldwide. As a first step, the acute and chronic effects of both commercial formulation and a.i. were quantified, and both formulations negatively affected the cladoceran's survival and reproductive parameters (age at first reproduction, number of offspring and number of broods), as well as the population's rate of increase. Whilst acute effects were comparable, the commercial formulation was slightly more toxic (EC50 was two-times lower) than the a.i. in chronic exposures, being prejudicial to D. longispina populations above 4.0mg/L of S-metolachlor. In a second experimental step, we focused on the potential multi-generational impacts of the exposure to the a.i. alone on biochemical (lipid biomarkers, namely fatty acids) and populational responses, because of the relevance of S-metolachlor as a biosynthesis inhibitor in many herbicidal formulations. The herbicide caused a significant decrease in Daphnia fecundity (in the size of the 1st clutch), but no concomitant alterations were found in fatty acid profiles of mothers or offspring. More important, this experiment showed that S-metolachlor did not cause effects in the subsequent generation, thus suggesting that biotic communities may recover after exposure to the xenobiotic.

A mixture of environmental organic contaminants in lake sediments affects hatching from Daphnia resting eggs.

Despite the relevance of resting eggs for ecology and evolution of many aquatic organisms and their exposure to contaminants accumulating in sediments, ecotoxicological studies using resting eggs are vastly underrepresented. The authors established a method to perform exposure assays with resting eggs produced by the Daphnia longispina species complex, key species in large lake ecosystems. A mixture of organic contaminants previously detected in sediments of Lake Greifensee was selected to test the potential effect of organic contaminants present in sediments on the hatching process. Resting eggs were exposed to a mix of 10 chemicals, which included corrosion inhibitors, biocides, pesticides, and personal care products, for a period of 15 d. Using an automated counting software, the authors found a significant increase in hatching success in the exposed resting eggs compared with controls. Such an effect has not yet been reported from ecotoxicological assays with resting eggs. Possible mechanistic explanations as well as the potential implications on the ecology and evolution of aquatic species that rely on a resting egg banks are discussed. Observed increased mortality and developmental abnormalities for hatchlings in the exposure treatments can be explained by toxic contaminant concentrations. The results of the present study highlight the need for additional studies assessing the effects of organic contaminants on resting egg banks and aquatic ecosystems.

Rotatoria–Cladocera–Copepoda relations in the long-term monitoring of water quality in lakes with trophic variation (E. Poland)

On the basis of long-term research (since the 1960s), changes were determined in zooplankton in five lakes located in the Łeczna-Wlodawa Lake District (E. Poland). During this time period, the region changed from being economically neglected and difficult to explore to being under intense human impact, with hydrological changes and deformations in the earth’s surface also taking place. This alteration was connected with substantial changes in abiotic variables in the lakes that were studied; these were accompanied by changes in species number, density and structure of zooplankton dominance as well as the ROT:CLA:COP ratio. The most highlighted changes in the zooplanktonic communities were a (1) decrease in zooplankton species richness in lakes showing strongest changes in water chemistry, (2) replacement of large cladocerans by smaller cladocerans with an increase in trophic status and inverse operation in the process of deeutrophication, (3) decrease in Rotatoria density in favour of Cladocera and Copepoda in the ROT:CLA:COP ratios along with the process of eutrophication, and inverse operation in the process of deeutrophication. The study showed that species of Brachionus, Filinia and Polyarthra as well as Bosmina longirostris are indicative of a long-term rise in water temperature; Trichocerca prefer elevated conductivity; the occurrence of Chydoridae species and some Daphnidae, including Ceriodaphnia quadrangula and Simocephalusvetulus coincides with a rising gradient in dissolved oxygen; Daphnia longispina and Monospilus dispar prefer waters with elevated N–NH4; Cyclops kolensis and Cyclops strenuus correlate with a rising gradient in P–PO4; and Eucyclops serrulatus, Eudiaptomus graciloides, and Macrocyclops albidus are indicative of elevated pH levels.

Assessment of Pollution in Sidi M'Hamed Benali Lake (Algeria) Based on Bioindicators and Physicochemical Parameters

A B S T R A C T This study was carried out to investigate the degree, the nature and the origin of pollution in Sidi M’hamed Benali Lake using the physicochemical parameters, saprobic index and cladocerans. For this purpose, water and zooplankton sampling was collected from six sites in lake during five seasons. The average seasonal values of physicochemical parameters showed that the lake undergoes a slight anthropogenic and natural pollution in the dry and wet periods. Presence of certain toxic substances (CN , Cr, Ni) require us to be more careful in irrigation, bathe and the consumption of fishes of that reservoir. Overall, oligo-mesosaprobic to beta-mesosaprobic rotifers have been prevailing in all five seasons indicating that the water was slightly or moderate polluted. The presence of Bosmina longirostris, Daphnia longispina, Daphnia cuculata, Daphnia ambiga and Sididae diaphonosoma brachyrum indicate bacterial contamination with the intense development of the phytoplankton in the lake, especially in springs and summer. Pearson correlation analysis revealed significant correlation between all of the physicochemical parameters. However, it revealed no significant correlation between zooplanktons occurrence and the majority environmental variables values. In present investigation, the Lake water is relatively little exposed to pollution and does not undergo strong organic pollution. doi: 10.5829/idosi.ijee.2015.06.04.09

Filamentous cyanobacteria alter the relative fitness in a Daphnia hybrid species complex

Summary Interspecific hybridisation is common in freshwater cladocerans. Within the Daphnia longispina complex hybrids frequently dominate over parental species, and environmental heterogeneity in the pelagial of lakes has been invoked to explain the coexistence of hybrids and parental species. In laboratory conditions, I investigated the effects of filamentous cyanobacteria on the relative fitness of Daphnia hyalina, Daphnia galeata and Daphnia hyalina×galeata hybrids. For each taxon, the performance of three clones was measured using animals fed with two diets: (i) a mixture of the filamentous cyanobacterium Cylindrospermopsis raciborskii and the green alga Scenedesmus obliquus and (ii) Scenedesmus obliquus in non‐limiting concentration. Inter‐ and intraspecific differences in ability to cope with cyanobacterial filaments were found; hybrids were, on average, superior to parental species in the absence of filaments, but in the presence of filaments one of the parental species (D. hyalina) was superior, while performance of hybrids did not differ from D. galeata. No relationship was found between size at first reproduction (range 1.3–2.0 mm) and reduced fitness due to the presence of cyanobacterial filaments. Shifts in relative fitness of daphnids due to variation in food quality, mediated by the presence of filamentous cyanobacteria, may promote coexistence of hybrids and parental species of the D. longispina complex.

Chronic aquatic effect assessment for the fungicide azoxystrobin.

The present study examined the ecological effects of a range of chronic exposure concentrations of the fungicide azoxystrobin in freshwater experimental systems (1270-L outdoor microcosms). Intended and environmentally relevant test concentrations of azoxystrobin were 0 µg active ingredient (a.i.)/L, 0.33 µg a.i./L, 1 µg a.i./L, 3.3 µg a.i./L, 10 µg a.i./L, and 33 µg a.i./L, kept at constant values. Responses of freshwater populations and community parameters were studied. During the 42-d experimental period, the time-weighted average concentrations of azoxystrobin ranged from 93.5% to 99.3% of intended values. Zooplankton, especially copepods and the Daphnia longispina group, were the most sensitive groups. At the population level, a consistent no-observed-effect concentration (NOEC) of 1 µg a.i./L was calculated for Copepoda. The NOEC at the zooplankton community level was 10 µg azoxystrobin/L. The principle of the European Union pesticide directive is that lower-tier regulatory acceptable concentrations (RACs) are protective of higher-tier RACs. This was tested for chronic risks from azoxystrobin. With the exception of the microcosm community chronic RAC (highest tier), all other chronic RAC values were similar to each other (0.5-1 µg a.i./L). The new and stricter first-tier species requirements of the European Union pesticide regulation (1107/2009/EC) are not protective for the most sensitive populations in the microcosm study, when based on the higher tier population RAC. In comparison, the Water Framework Directive generates environmental quality standards that are 5 to 10 times lower than the derived chronic RACs.

Diversity of the Daphnia longispina species complex in Chinese lakes: a DNA taxonomy approach

Cladocerans of the Daphnia longispina complex are often the key components of pelagic food webs in northern temperate lakes and ponds. In the present study, we aimed to fill the gap in knowledge on the biogeography and diversity of this species complex, through analysis (by sequencing two mitochondrial genes) of the taxonomic structure of 18 lake populations across China, covering a large geographical and ecological range. Based on the patterns observed in the Western Palaearctic and Japan, we hypothesized that several species of the D. longispina complex should coexist and that some cryptic lineages are present in China. In the lakes studied, however, we detected haplotypes of only two species (D. galeata and D. dentifera). Daphnia galeata was detected in eutrophic lakes at lower altitudes (in central and eastern China), whereas D. dentifera was found in high-altitude oligotrophic lakes of the Tibetan Plateau in western China. The two lineages coexisted in only one of the lakes studied, in Tibet. The variation in mitochondrial DNA differed between the two species. Daphnia dentifera haplotypes were lake specific, while D. galeata haplotypes were often shared across lakes and geographic regions, indicating a recent rapid expansion of the latter species.

REDESCRIPTION OF DAPHNIA LONGISPINA (CRUSTACEA: CLADOCERA), INHABITING EGYPTIAN WATER WITH SPECIAL REFERENCE ON ITS FILTER THORACIC APPENDAGES

Specimens of cladoceran zooplankton including Daphnia longispina were collected from three different fresh water streams around Kafr El-zayat, North Delta region, Egypt. They were microscopically examined and identified. Detailed morphological and morphometric studies were carried out of Daphnia logispina. Because of the importance of the trunk limbs of D. longispina, which are responsible for feeding and are modified to extract food particles from the water in which it lives, the limbs were examined with a scanning electron microscope after double fixation and critical point drying techniques. The study revealed some fine structures of these limbs and setae. Their morphology and arrangement as well as their armature, were revealed by SEM observations, the armature of limbs 3 and 4 dominates the trunk limb complex and make up an extensive filter chamber.