Daphnia Longispina Complex Research Articles

Mitochondrial sequence variation suggests extensive cryptic diversity within the Western Palearctic Daphnia longispina complex

We report on a discovery of six divergent lineages within the European Daphnia longispina complex from various localities in central to northeast Europe. The levels of divergence from well‐known species of the complex suggest that they represent as yet unrecognized distinct taxa. These newly recognized lineages always coexisted in syntopy with widespread species of the complex. Particularly rich in cryptic diversity (with four of the six lineages present) was the delta of the River Pechora in northern European Russia, a region not covered by an ice sheet during most of the last glacial period. We suggest that ice‐free regions of northeastern Europe may have been important refugia for planktonic species, and still are overlooked hot spots of diversity. Our findings confirm that the real diversity within widespread crustacean planktonic taxa is much higher than presently recognized. The potential presence of cryptic species should be considered in ecological studies.

At the edge and on the top: molecular identification and ecology of Daphnia dentifera and D. longispina in high-altitude Asian lakes

The occurrence of members of the highly diverse Daphnia longispina complex in Southern and Central Asian high-mountain lakes has been recognized for more than a century. Until now, however, no molecular data have been available for these populations inhabiting the “Roof of the World.” Here, we present the first identification for D. gr. longispina from that region based on a molecular phylogeny. Our findings show that alpine lakes in the Pamir and Himalaya mountains host populations of widespread species of the complex, for which these are the highest known localities. A spineless morph from the Himalaya region, previously labeled as D. longispina var. aspina, was clustering tightly with D. dentifera, while a population from the Pamir mountain range was grouped with D. longispina. In addition, we analyzed ecological data available for lakes in the Khumbu region (Himalaya) to investigate ecological preferences of non-pigmented D. gr. longispina. The identified factors can at least partly be related to avoidance of high UV conditions by this species. We conclude that the widespread species D. dentifera and D. longispina also colonized the Asian high-mountain lakes, and identify the need for further research to trace the possible effect of rapid environmental changes in this region on the diversity and ecology of high-altitude Daphnia populations.

Interspecific hybridization in sympatric species of Daphnia inhabiting lakes in northeastern Poland

Abstract Populations of three sympatric species (Daphnia cucullata, Daphnia galeata, and Daphnia hyalina (Daphnia longispina complex)) inhabiting three lakes in northeastern Poland (Roś, Mikołajskie, Wigry) were checked for interspecific hybrids. Hybrid Daphnia coexisting with parental individuals were detected in each of the investigated lakes. Several classes of hybrids (F1, F2, backcrosses), including D. cucullata×galeata×hyalina individuals, have been detected. Hybrids constituted a substantial (13%–38%) part of the total abundance of individuals of the D. longispina complex. Deficiency of heterozygotes (hybrids) detected may indicate the existence of barriers for gene flow between the sympatric Daphnia taxa.

Fine-scale temporal and spatial variation of taxon and clonal structure in the Daphnia longispina hybrid complex in heterogeneous environments

BackgroundCyclical parthenogenetic water fleas of the genus Daphnia have become a prominent model organism in ecology and evolution. In the past, analyses of their population structure have been limited by the prevailing use of allozyme markers, which in general do not allow for the distinction of individual clones. In this study, we used 10 microsatellite markers to track changes in the taxonomic and clonal composition of Daphnia populations, and traced the abundance of the most common clones in two European reservoirs. One of the localities was inhabited by a single species of the Daphnia longispina complex (D. galeata), the other by two parental species (D. galeata and D. longispina) and their interspecific hybrids. The study took place during the transition from summer stratification to autumn mixing, representing a period of major environmental change within lake habitats.ResultsIn both reservoirs, we observed temporal (generation-to-generation) and spatial (along the heterogeneous reservoir environment) changes in Daphnia community structure. In the single-species reservoir, the clonal diversity of D. galeata increased with time, as a few dominant clones were replaced by a higher number of less common clones. A loss in selective advantage for the dominant clones may have been due to gradual changes in the environment, or due to selection acting in a negative frequency-dependent manner. In the multispecies reservoir, there were no apparent temporal trends in clonal diversity but we observed significantly lower clonal diversity in the interspecific hybrids than in the coexisting parental species, supporting the existence of reproductive barriers between the parental genomes.ConclusionsOur study, tracing clonal lineages of Daphnia in time and space by the fine-resolution markers, contributes to the understanding of how clonal reproduction impacts community structure in cyclically parthenogenetic organisms.

Effects of extreme floods on the Daphnia ephippial egg bank in a long narrow reservoir

Ephippial egg banks are important reservoirs of dormant stages that allow the recovery of Daphnia populations after unfavourable periods. Although the contribution of hatchlings from ephippia to a population in the water column is probably of minor importance in permanent water bodies with a year-round Daphnia persistence, this may differ after major disturbances. In 2006, two 500-year floods hit the long and narrow Vranov Reservoir (Czech Republic), in which we had investigated zooplankton densities and ephippia distribution in the sediment in preceding years. In this study, we evaluated the impact of those extraordinary floods on the population of the Daphnia longispina complex, and particularly on the local dormant egg bank. We considered two alternative hypotheses related to the egg bank: that either the substantial input of new material with the flood completely buried and therefore reset the existing egg bank, or that the sediment including ephippia was redistributed in the reservoir after the flood and dormant eggs could be exposed to hatching stimuli. A year after the floods, we did not observe any sediment layer that would be devoid of ephippia. However, we observed a significant increase in the proportion of empty ephippia and a decrease in the proportion of those containing eggs. We attribute these changes to disturbance of the sediment due to the floods, which caused redistribution of ephippia stored in the sediment and those detached from the reservoir shoreline. Dormant eggs inside ephippia deposited to shallow parts of reservoir after the floods could therefore receive and respond to hatching stimuli. Hatching from ephippia may have contributed to Daphnia recovery after the spring flood; however, a significant proportion of the Daphnia population probably survived the summer flood protected in the epilimnetic refuge of the thermally stratified environment.

Clonal diversity, clonal persistence and rapid taxon replacement in natural populations of species and hybrids of the Daphnia longispina complex

Hybridization is common among cyclical parthenogens, especially in zooplankton species assemblages of the genus Daphnia. To explore hybridization dynamics and the extent of clonal diversity in the Daphnia longispina complex, we analysed population structure in eight permanent lakes. Based on 15 microsatellite loci, three major taxonomic units emerged: two species, D.galeata and D.longispina and their F1 hybrids, supported by factorial correspondence analysis and two Bayesian methods. At the same time, the detection of backcross classes differed between methods. Mean clonal diversity was lowest in the F1 hybrids, as expected from the high rate of asexual reproduction. Within taxa, replicated genotypes were of clonal origin, but clonal lineages persisted in subsequent years in only one of three resampled lakes. In another lake, the taxon composition changed from being dominated by hybrids to complete dominance by one parental taxon. Such a year-to-year taxon replacement has not been reported for the D.longispina complex before. Our data on this hybrid complex illustrate that high-resolution genotyping is essential for the understanding of ecological and evolutionary outcomes of hybridization in partially clonal taxa.

The stabilizing effect of resting egg banks of the Daphnia longispina species complex for longitudinal taxon heterogeneity in long and narrow reservoirs

We compared the spatial distribution of taxa from the Daphnia longispina complex (D. longispina, D. galeata, D. cucullata, and their hybrids) in the active water column community and in resting egg banks in five long narrow reservoirs in the Czech Republic (Central Europe). In each reservoir, we sampled at both ends of the longitudinal gradient: in the inflow region and at the dam. Ephippia abundance in the sediments significantly increased in the downstream direction, reflecting differences in the sedimentation regime and Daphnia population size. Similarly to the active zooplankton community, in which D. cucullata and D. longispina tended to occur at opposite ends of the reservoirs, Daphnia species and interspecific hybrids in resting eggs revealed a spatially diversified pattern; however, we observed some differences in taxon distributions between sediments and water columns. High relative abundances of hybrid genotypes (up to 16% of resting eggs, and 74% of Daphnia in the water column) confirm that interspecific hybridization is frequent in these reservoirs, and some hybrids are successful in competition with the parental taxa. We assume that the spatial heterogeneity of Daphnia taxonomic composition in reservoirs, being affected by the seasonal selection of taxa within the mixed reservoir species pool, is substantially strengthened by the presence of spatially heterogeneous egg banks.

A taxonomic reappraisal of the European Daphnia longispina complex (Crustacea, Cladocera, Anomopoda)

The Daphnia longispina complex contains some of the most common water flea species in the northern hemisphere, and has been a model organism for many ecological and evolutionary studies. Nevertheless, the systematics and nomenclature of this group, in particular its Palaearctic members, have been in flux for the past 150 years; this hinders the correct interpretation of scientific results and promotes the erroneous use of species names. We revise the systematics of this species complex based on mitochondrial sequence variation (12S rDNA and COI) of representative populations across Europe, with a special focus on samples from type localities of the respective taxa. Combining genetic evidence and morphological assignments of analysed individuals, we propose a comprehensive revision of the European members of the D. longispina complex. We show that D. hyalina and D. rosea morphotypes have evolved several times independently, and we find no evidence to maintain these morphotypes as distinct biological species. Alpine individuals described as D. zschokkei are conspecific with the above‐mentioned lineage. We suggest that this morphologically and ecologically plastic but genetically uniform hyalina–rosea–zschokkei clade should be identified as D. longispina (O. F. Müller, 1776). The valid name of Fennoscandian individuals labelled D. longispina sensu stricto in the recent literature is D. lacustris G. O. Sars, 1862. Additionally, we discovered another divergent lineage of this group, likely an undescribed species, in southern Norway. Our results present a solution for several prevailing taxonomic problems in the genus Daphnia, and have broad implications for interpretation of biogeographical patterns, and ecological and evolutionary studies.

Biochemical food quality effects on a Daphnia hybrid complex

Correlative field studies have shown that the food quality of natural seston for Daphnia is highly correlated with the content of eicosapentaenoic acid (EPA), indicating that the growth of Daphnia in nature is at least seasonally limited by a low availability of this polyunsaturated fatty acid. Here we test the hypothesis that a putative limitation due to limited availability of EPA in natural seston should lead to genetic adaptation in physiological traits reflected in genotype‐dependent differences in the ability of sympatric clones of Daphnia to cope with these shortages. We further test if this adaptation to the low availability of EPA provides another explanation for the coexistence of hybrids with their parental taxa. Standardized growth experiments were performed with and without dietary EPA using clones of three taxa from the Daphnia longispina complex: Daphnia galeata, Daphnia hyalina, and their interspecific hybrids. Fitness was estimated from juvenile somatic growth rates, g, and from intrinsic population growth rates, r. There was marked interclonal variability in the susceptibilities of g and r to the absence of EPA from the food, with considerable intraspecific variability. At the taxon level, we noted differences in susceptibility to EPA limitation with regard to the intrinsic rate of population increase r, which demonstrates that the availability of EPA affects the relative fitness of hybrids, but not of the parental species. On average, hybrids seemed less susceptible to the absence of EPA than do parental species. Environmental heterogeneity driven by EPA‐mediated changes in the quality of food may in consequence contribute to the maintenance of genetic diversity in Daphnia and may be a reason for the temporal dominance of hybrids.

Intra-specific rDNA-ITS restriction site variation and an improved protocol to distinguish species and hybrids in the Daphnia longispina complex

A collaborative research effort was undertaken to evaluate the robustness of a recently developed genetic tool for species identification of members in the morphologically variable Daphnia longispina species complex. This genetic method, based on restriction fragment length polymorphism (RFLP) of the internal transcribed spacer region (ITS) of nuclear ribosomal DNA (rDNA) with restriction enzymes Mwo I and Sau96 I [Billiones et al., 2004. Hydrobiologia 526: 43–53], was applied to many different European populations. Results were compared with two or more independently obtained characters (morphology, allozymes, mitochondrial DNA (mtDNA), or cloned rDNA-ITS sequences). Individuals of most taxa were readily identified, but unexpected ITS-RFLP patterns were found in many individuals indicated by other markers to be D. galeata or one of its hybrids. Among 43 investigated D. galeata populations (902 specimen analysed by ITS-RFLP), deviant RFLP fragment patterns occurred in 26 (i.e., more than half) of the populations. The deviant patterns could be attributed to the loss of one single restriction site in the ITS2 region. This loss made the distinction of D. galeata from other species unreliable, and F1 hybrids could not be identified. Future users should be aware of this shortcoming of the Billions et al. [2004. Hydrobiologia 526: 43–53] protocol. As a solution to this problem, we present an improved genetic identification protocol based on a simple double digestion of the rDNA-ITS region with the restriction enzymes BsrB I and EagI. Sequence analyses of rDNA-ITS clones and preliminary testing indicate that the new protocol is unaffected by the rDNA variation which troubled the Mwo I/Sau96 I protocol. Further, the new protocol identifies all European species of the D. longispina complex, as well as their F1 hybrids. However, a wider screening is required to verify its general utility for all species, since yet unknown variation may occur.

Effects of food availability on the acute and chronic toxicity of the insecticide methomyl to Daphnia spp.

The widespread increase of pesticides application in crops threats vicinal freshwater lentic ecosystems, frequently leading to their contamination. Due to their position in the aquatic food web, the responses to these pesticide inputs of freshwater filter-feeding zooplankters, as daphnids, provide relevant information the general risk to the ecosystem of xenobiotics. Moreover, cladoceran grazers often face fluctuations in food availability due to the phytoplankton dynamics in lentic water bodies, and food acquisition naturally conditions their fitness. In this study, the responses of Daphnia magna, and of three genotypes within the Daphnia longispina complex, to acute and chronic exposures of methomyl, were assessed. In addition, we focused on whether the food level can model the Daphnia life-history responses to the insecticide. Results showed that methomyl was acutely and chronically toxic to both D. magna and the D. cf longispina populations at very low concentrations, and remarkable differences in sensitivity were noticed when comparing the responses to the toxic among taxa/genotypes. Furthermore, food availability conditioned the overall fitness of the species although not interacting specifically on the response to the toxicant stress.

Short- and long-term responses of Daphnia spp. to propanil exposures in distinct food supply scenarios

The widespread increase of pesticides application in crops frequently leads to the contamination of vicinal freshwater lentic ecosystems. Herbicides such as propanil may impair cladoceran fitness, which is per se strongly influenced by the food availability and/or its acquisition efficiency. This work intended to evaluate the responses of Daphnia magna and three clonal lineages belonging to the Daphnia longispina complex to acute and chronic exposures of the herbicide propanil, as well as to assess whether food availability features these responses. Results showed that the agrochemical was acutely and chronically toxic to both D. magna and the D. cf. longispina clones at the same range of low concentrations, while relevant differences were depicted between the three distinct genotypes belonging to the D. longispina complex. Food-level conditioned the general fitness of the daphnids in the tests but evidences suggest that it does not interfere specifically with the toxicant mode of action.

Genetic assessment of species boundaries in the North American Daphnia longispina complex (Crustacea: Daphniidae)

Abstract Species boundaries in the North American Daphnia longispina group have proved difficult to establish on the basis of morphology alone. This confusion may be due to hydridization, phenotypic plasticity or the existence of sibling species. We therefore used genetic analysis to delineate species boundaries by examining 27 North American populations belonging to the longispina complex for variation at 15-26 allozyme loci. The populations consisted of Daphnia thorata from two western sites and two eastern sites, Daphnia galeata mendotae from its type location and seven sites across its range, and Daphnia rosea from eight temperate and seven arctic sites. Two populations from the Eurasian longispina complex were also included for reference. Populations assigned to D. galeata mendotae formed a genetically cohesive group, whereas a genetic dichotomy was found between temperate and arctic D. rosea, suggesting that this taxon includes two species. Genetic analysis also confirmed the distinctness of western D. thorata from other members of the longispina group. Unexpectedly, eastern populations resembling D. thorata were genetically more similar to temperate D. rosea than to any helmeted species (D. galeata, Daphnia hyalina or D. thorata). Our results suggest that the helmet character is a poor indicator of phylogenetic relationships, as the genetic ability to produce this feature has been lost or acquired several times in the evolution of the longispina group.

Genetic assessment of species boundaries in the North American Daphnia longispina complex (Crustacea: Daphniidae)

Species boundaries in the North American Daphnia longispina group have proved difficult to establish on the basis of morphology alone. This confusion may be due to hydridization, phenotypic plasticity or the existence of sibling species. We therefore used genetic analysis to delineate species boundaries by examining 27 North American populations belonging to the longispina complex for variation at 15-26 allozyme loci. The populations consisted of Daphnia thorata from two western sites and two eastern sites, Daphnia galeata mendotae from its type location and seven sites across its range, and Daphnia rosea from eight temperate and seven arctic sites. Two populations from the Eurasian longispina complex were also included for reference. Populations assigned to D. galeata mendotae formed a genetically cohesive group, whereas a genetic dichotomy was found between temperate and arctic D. rosea, suggesting that this taxon includes two species. Genetic analysis also confirmed the distinctness of western D. thorata from other members of the longispina group. Unexpectedly, eastern populations resembling D. thorata were genetically more similar to temperate D. rosea than to any helmeted species ( D. galeata, Daphnia hyalina or D. thorata). Our results suggest that the helmet character is a poor indicator of phylogenetic relationships, as the genetic ability to produce this feature has been lost or acquired several times in the evolution of the longispina group.