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.     

A description of pelagic zooplankton in the large lakes of the Todzha Depression (Bolshoi Yenisey River basin, Tuva)

The zooplankton structure of large lakes (Noyon-Khol’, Shuram-Khol’, Borzu-Khol’, Many-Khol’, Kadysh, and Todzha) of the Todzha Depression has been studied. A comparison of the species composition, abundance, and biomass of zooplankton in the lakes was made. Rotifers have the largest species diversity: from 10 to 16 species, with Conochilus sp., Collotheca sp., Kellicottia longispina (Kellicott), and Asplanchna priodonta Gosse being the most abundant. Copepods are represented mostly by Arctodiaptomus paulseni (Sars), Eudiaptomus graciloides (Lilljeborg), Cyclops scutifer Sars, and Mesocyclops leuckarti Claus. Daphnia galeata Sars and Bosmina longispina Leydig are the dominant cladoceran species. It is shown that the zooplankton communities of the lakes in the Todzha Depression are characterized by a high degree of species composition similarity. Factors forming the taxonomic structure of pelagic zooplankton in the system of these lakes are displayed.     

Restoring <Emphasis Type="Italic">Daphnia lacustris</Emphasis> G.O. Sars, 1862 (Crustacea,Anomopoda): a cryptic species in the <Emphasis Type="Italic">Daphnia longispina</Emphasis> group

While molecular markers have revealed several distinct species within the Daphnia longispina group, there is a need to reconcile these species with traditional nomenclature. Here we show that one such species, called D. longispina in recent literature based on molecular markers, can reliably be associated with the described taxon Daphnia lacustris G.O. Sars, 1862. Both mitochondrial and nuclear molecular markers readily distinguish this species from others in the D. longispina group. D. lacustris is absent in the region from which D. longispina was first described (Denmark), and the designation D. longispina must be reserved for another widespread species represented by Danish lineages. While the diagnosis of D. lacustris (and other species of the D. longispina group) by molecular markers is unequivocal, distinguishing it morphologically from other species is still problematic. The presently known distribution range of D. lacustris includes most of Norway, northern Finland and a single lake in the Polish Tatra Mountains. Its typical habitat is oligotrophic lakes without intense fish predation. Guest editor: Piet Spaak Cladocera: Proceedings of the 7th International Symposium on Cladocera     

Molecular genetic identification and phylogeny of Daphnia species (Crustacea, Cladocera) from water bodies of the Lake Chany basin

The data on the molecular genetic identification of Daphnia species from the water bodies of the Lake Chany basin are presented. Phylogenetic relationships between these species have been established. The fragments of the mitochondrial DNA genes were used as genetic markers. According to the data obtained, the water bodies examined were inhabited by five Daphnia species, including Daphnia (Daphnia) galeata Sars, D. (D.) longispina O. F. Müller, D. (D.) curvirostris Eylmann, D. (D.) pulex Leydig, and D. (Ctenodaphnia) magna Straus. In addition, longispina a-like individuals that form a separate phylogenetic lineage was identified.     

Depth-selection behavior and longevity in Daphnia: an evolutionary test for the predation-avoidance hypothesis

The classic evolutionary theory of senescence predicts that long lifespan evolves under low risk of extrinsic mortality. As lakes present planktonic animals with vertical gradients of mortality risk associated with fish predation, we expected the individual lifespan of Daphnia of the “hypolymnetic” clones to be longer than that of “epilimnetic” Daphnia. In order to test this prediction, we performed a laboratory study on 14 clones from the D. longispina species complex, taken during the daytime either from epilimnion or hypolimnion of three mesotrophic lakes. “Epilimnetic” Daphnia started reproduction earlier, aged faster, and lived shorter than their “hypolimnetic” conspecifics. Our results indirectly support the predation-avoidance hypothesis as the ultimate explanation for depth-selection behavior in Daphnia.     

Identifying century-old long-spined <Emphasis Type="Italic">Daphnia</Emphasis>: species replacement in a mountain lake characterised by paleogenetic methods

Mountain lakes often harbour morphologically or genetically unique populations of zooplankton species, including cladocerans. Daphnia lacustris Sars, predominantly found in Fennoscandia but also known from two Central European lakes in the Tatra Mountains, is one of such taxa. This Daphnia species often forms morphotypes with extremely long tailspines. Historical literature from a century ago documented similar morphs from another lake in the Tatra mountain range, presently inhabited by the phenotypically very different D. galeata. Using a paleogenetic approach (partial sequencing of the mitochondrial gene for 12S rRNA from preserved ephippial eggs in the lake sediment), we tested the hypothesis that Daphnia species composition changed in the lake due to anthropogenic disturbances, and that long-spined morphs were actually another relict population of currently extinct D. lacustris. Ephippia with extremely long spines were successfully retrieved from sediment cores. Despite being morphologically very well preserved, intact eggs were found in less than 2% of analysed ephippia. Genetic analyses, benefiting in most cases from amplification of short 12S fragments using internal primers, proved that long-spined ephippia belonged to D. longispina, which apparently coexisted with D. galeata in the mid-twentieth century. Our results confirm that paleogenetic methods are useful for studying the recent population structures of zooplankton species forming dormant egg banks but lacking reliably identifiable remains in sediments, and show that the extreme development of tailspines in mountain-lake Daphnia is associated with as-yet unclear environmental factors rather than taxonomic status.     

Identifying hybridizing taxa within the <Emphasis Type="Italic">Daphnia longispina</Emphasis> species complex: a comparison of genetic methods and phenotypic approaches

Daphnia galeata Sars, D. longispina O. F. Müller and D. cucullata Sars (Crustacea: Cladocera) are closely related species which often produce interspecific hybrids in natural populations. Several marker systems are available for taxon determination in this hybridizing complex, but their performance and reliability has not been systematically assessed. We compared results from identifications by three molecular methods. More than 1,200 individuals from 10 localities in the Czech Republic were identified as parental species or hybrids by allozyme electrophoresis and the analysis of the restriction fragment length polymorphism of the internal transcribed spacer (ITS-RFLP); over 440 of them were additionally analyzed and identified by 12 microsatellite loci. Identification by microsatellite markers corresponded well with allozyme analyses. However, consistent discrepancies between ITS-RFLP and other markers were observed in two out of 10 studied localities. Although some marker discrepancies may have been caused by occasional recent introgression, consistent deviations between ITS-RFLP and other markers suggest a long-term maintenance of introgressed alleles. These results warn against its use as a sole identification method in field studies. Additionally, we quantitatively evaluated the discriminatory power of geometric morphometric (elliptic Fourier) analysis of body shapes based on photos of over 1,300 individuals pre-classified by allozyme markers. Furthermore, a randomly selected subset of 240 individuals was independently determined from photos by several experts. Despite a tendency for morphological divergence among parental Daphnia species, some taxa (especially D. galeata, D. longispina, and their hybrids) substantially overlapped in their body shapes. This was reflected in different determination success for particular species and hybrids in discriminant analysis based on shape data as well as from photographs.     

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.     

Aging in Brachionus plicatilis: The evolution of swimming as a function of age at two different calcium concentrations

Species composition and density of cladoceran populations changed in Lakes Zürich, St. Mortiz and Baldegg as human populations increased in these watersheds. Lake Zürich sediments became annually laminated in the 1890's as a result of increased organic input as the size of the cities surrounding the lake grew. At the same time, the Bosmina species changed from a oligotrophic form (longispina) to a eutrophic form (longirostris). An increase in Daphnia spp. populations also occurred at this time in the lake's history. Bosmina longispina reappeared in the lake in 1965 as the lake's trophic status changed from eutrophic to mesotrophic due to effective sewage treatment facilities. Annual laminations appear in the Lake St. Moritz sediments about 1910. Shortly thereafter, a shift from B. longispina to B. longirostris occurred. This change in trophic status is associated with increased tourism in the area. Lake Baldegg sediments also show annual laminations beginning in 1885 and a similar shift in the Bosmina species. Other cladoceran remains were too scarce to be useful in interpreting the histories of these lakes.     

Daphnia diversity on the Tibetan Plateau measured by DNA taxonomy

Daphnia on the Tibetan Plateau has been little studied, and information on species diversity and biogeography is lacking. Here, we conducted a 4‐year survey using the barcoding fragment of the mitochondrial COI gene to determine the distribution and diversity of Daphnia species found across the Plateau. Our results show that species richness is higher than previously thought, with total described and provisional species number doubling from 5 to 10. Six of the taxonomic units recovered by DNA taxonomy agreed well with morphology, but DNA barcoding distinguished three clades each for the D. longispina (D. galeata, D. dentifera, and D. longispina) and D. pulex (D. pulex, D. cf. tenebrosa, and D. pulicaria) complexes. The sequence divergence between congeneric species varied within a large range, from 9.25% to 30.71%. The endemic D. tibetana was the most common and widespread species, occurring in 12 hyposaline to mesosaline lakes. The lineage of D. longispina is the first confirmed occurrence in west Tibet.     

Using morphological characters of subfossil daphniid postabdominal claws to improve taxonomic resolution within species complexes

Daphnia subfossils from lake sediments are useful for exploring the impacts of environmental stressors on aquatic ecosystems. Unfortunately, taxonomic resolution of Daphnia remains is coarse, as only a small portion of the animal is preserved, and so the identification of daphniid subfossils typically relies upon postabdominal claws. Daphniid claws can be assigned to one of two species complexes: D. longispina or D. pulex. Both complexes contain species with differing environmental optima, and therefore improved taxonomic resolution of subfossil daphniid claws would aid paleolimnological analyses. To identify morphological features that may be used to help differentiate between species within complexes, we used species presence/absence data from net tows to select lakes in central Ontario (Canada) containing only a single species from a particular complex, then used remains preserved in surface sediments of these lakes to isolate four Daphnia species: D. ambigua and D. mendotae from the D. longispina complex, and D. pulicaria and D. catawba from the D. pulex complex. Our analyses demonstrate that, within the D. longispina complex, postabdominal claw length (PCL) and spinule length can be used to distinguish D. mendotae from D. ambigua. In addition, within the D. pulex complex, there are differences between D. pulicaria and D. catawba in the relative lengths of the proximal and middle combs on the postabdominal claw. However, the number of stout spines on the middle comb is an unreliable character for differentiating species. Overall, our data demonstrate that greater resolution within Daphnia species complexes is possible using postabdominal claws; however, the process is arduous, and applicability will likely decrease with the number of taxa present.     

Restoration of zooplankton in a small acidified mountain lake (Plešné Lake,Bohemian Forest) by reintroduction of key species

Atmospheric acidification brought about the extinction of several species of planktonic Crustacea in lakes of the Bohemian Forest (?umava, Böhmerwald). The recent reversal in chemical parameters of lake water towards pre-acidification values raises the question whether the return of missing species is possible. We have designed a bioassay to test water from different lakes for the survival of Daphnia longispina, which inhabited the lakes under study but disappeared from those most affected by acidification. The bioassay showed the best survival in water from Ple?né Lake, one of those where Daphnia and Cyclops became extinct. A large-scale experiment was conducted by transplanting Daphnia longispina (Crustacea, Cladocera) and Cyclops abyssorum (Crustacea, Copepoda) from Prá?ilské Lake, where they have survived until the present, to Ple?né Lake. One year later, a successful reintroduction was confirmed for Cyclops abyssorum.     

Species distribution modeling and machine learning in assessing the potential distribution of freshwater zooplankton in Northern Italy

Species distribution models (SDM's) are powerful tools used to describe species suitable habitats and spatial occurrences and many statistical methods and algorithms are available to model the spatial distribution of a target species. Here we explore a species distribution model framework combined with machine learning algorithms to describe the distribution of two freshwater zooplankton species Daphnia longispina (Cladocera) and Eucyclops serrulatus (Copepods) in a system of 283 shallow and ephemeral freshwater habitats in the Northern Italian Appennines. For each species, we model the habitat suitability by comparing one regression-based model, one generalized linear model (GLM) and two machine learning algorithms: random forest (RF) and artificial neural network (ANN) with one hidden layer. We used a total of 27 predictor variables. The modeling framework was used considering a scenario of future climate change in order to evaluate potential shifts in spatial distribution of the zooplankton species. For both species, the supervised machine learning algorthn (ANN) produced the highest mean values for all the performance metrics. For D. longispina and E. serrulatus, the two most important variables ranked by the shap analysis and global sensitivity and uncertainty analysis (GSUA) were temperature seasonality and precipitation of the warmest quarter. Both species, in a future climatic change scenario, are expected to shift their distribution mainly toward lower northern altitudes with an overall expansion of 7% with respect to the past/present climatic conditions. However, the spatial expansion of D. longispina and E. serrulatus was qualitatively different. In agricultural and natural areas, the expansion of E. serrulatus was greater than that of D. longispina but, in natural areas, the expansion of E. serrulatus was counterbalanced by a greater spatial contraction than that of D. longispina. As hypothesized, direct and indirect anthropogenic pressures may affect the predicted potential shift and expansion of the zooplankton species.     

Acidification and the structure of crustacean zooplankton in mountain lakes: The Tatra Mountains (Slovakia,Poland)

Species composition of planktonic Crustacea in 102 lakes in the West and High Tatra Mountains, studied during the peak of anthropogenic acidification (1978–1996), is presented in this work. Zooplankton of the Tatra lakes have been studied since the middle of the 19^th century, which later enabled the recognition of lake acidification and the assessment of its effect on the plankton community of lake ecosystems. In the pre-acidification period, the distribution of zooplankton was determined namely by the lake altitude and orientation (north vs. south) and by the catchment character. Crustacean zooplankton in larger lakes consisted of a limited number of species, with Acanthodiaptomus denticornis and Daphnia longispina dominating lakes in the forest zone, and Arctodiaptomus alpinus, Cyclops abyssorum, Daphnia longispina, Daphnia pulicaria, and Holopedium gibberum dominating lakes in the alpine zone. Ceriodaphnia quadrangula, Daphnia obtusa, Daphnia pulex, and Mixodiaptomus tatricus occurred in lakes with high concentrations of dissolved organic matter and in strongly acidified waters. Anthropogenic acidification has caused drastic changes in both the chemistry and biology of the Tatra lakes. Based on their status during the acidification peak, lakes were divided into three categories: non-acidified (with no change in the species composition of crustacean zooplankton due to the acidification), acidified (planktonic Crustacea disappeared in lakes with meadow-rocky catchments), and strongly acidified lakes where original Crustacea in meadow-rocky catchment lakes disappeared and were replaced by populations of the acid-tolerant littoral species Acanthocyclops vernalis, Chydorus sphaericus, and Eucyclops serrulatus. The acidification-induced processes of oligotrophication and toxicity of aluminium played a key role in the extinction of species. Despite the first signs of biological recovery observed in the early 2000s, acidification remains the most important factor governing the structure of plankton in the Tatra lakes.     

The late Holocene appearance of European Bosmina (Eubosmina) thersites (Crustacea, Cladocera) in lakes surrounding the Baltic Sea

This study shows the appearance of Bosmina (Eubosmina) thersites during the last millennium in two lakes in Northern Europe: Lake Charzykowskie (Poland) and Lake Lohja (Estonia). Cladocera remains collected from both lakes showed similar Bosmina species composition and changes during the late Holocene. Older sediment layers showed a prevalence of smaller Eubosmina species (B. (E.) longispina), indicating oligotrophic conditions of the lakes, while younger layers were dominated by larger species (B. (E.) coregoni and B. (E.) thersites), typically found in lakes with higher trophy. The presence of B. (E.) thersites has rarely been reported in paleolimnological research, and this is the first observance of its high abundance in lake sediments. More research is needed, however, to better understand the appearance, speciation driver, continental range, and ecological preferences of B. (E.) thersites.     

Major changes in pelagic rotifers during natural and forced recovery from acidification

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.     

Notes on Cladocera and Copepoda from high altitude lakes in the Mount Everest Region (Nepal)

The paper deals with Cladocera and Copepoda species from eight high altitude lakes in the Khumbu area. In all lakes, an endemic known diaptomid of the palearctic genus Arctodiaptomus is found. The dark and large Daphnia tibetana occurs in five of the lakes sampled, characterized by the persistence of the spine in adults (parthenogenetic and ephippial females, males). Apparently, this is an unknown feature of this species. The literature on the diagnostic traits of the different morphs described is reviewed. In addition, a transparent and smaller-sized Daphnia species occurs in two lakes. This is a D. longispina characterized by the absence in adults of the carapace spine (var. aspina Weretschagin, 1911). The presence of these two species is discussed in relation to water transparency, colour, and vertical distribution. Two hypotheses on the evolution of cuticular pigmentation in Daphnia are examined. In addition to these mostly dominant species, a macrothricid also typical of high altitude lakes in the Alps was found (Macrothrix hirsuticornis) together with two cosmopolitan Chydoridae.     

Genetic Structure of Daphnia galeata Populations in Eastern China

This study presents the first examination of the genetic structure of Daphnia longispina complex populations in Eastern China. Only one species, D. galeata, was present across the eight investigated lakes; as identified by taxon assignment using allelic variation at 15 microsatellite loci. Three genetically differentiated D. galeata subgroups emerged independent of the type of statistical analysis applied. Thus, Bayesian clustering, discriminant analysis based on results from factorial correspondence analysis, and UPGMA clustering consistently showed that populations from two neighbouring lakes were genetically separated from a mixture of genotypes found in other lakes, which formed another two subgroups. Clonal diversity was high in all D. galeata populations, and most samples showed no deviation from Hardy-Weinberg equilibrium, indicating that clonal selection had little effect on the genetic diversity. Overall, populations did not cluster by geographical origin. Further studies will show if the observed pattern can be explained by natural colonization processes or by recent anthropogenic impact on predominantly artificial lakes.     

Effects of recent acidification on Cladocera in small clear-water lakes studied by means of sedimentary remains

Cladoceran populations, as revealed by sedimentary remains, were studied in six lakes which by diatom evidence have become strongly acidified during the past 30 years. The accumulation rates of cladoceran remains and in two of the most strongly acidified lakes both relative and absolute numbers ofBosmina greatly increased during this period. Species numbers were not reduced, but there were shifts in relative abundances of cladoceran species.Bosmina longispina dominated all the lakes. Low pH (4.7) seemed not to be straight-forwardly harmful toDaphnia longispina, but the relative abundances of this taxon were reduced because ofBosmina.