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Predation has been a major driver of the evolution of prey species, which consequently develop antipredator adaptations. However, little is known about the genetic basis underpinning the adaptation of prey to intensive predation. Here, we describe a high-quality chromosome-level genome assembly (approx. 145 Mb, scaffold N50 11.45 Mb) of Daphnia mitsukuri , a primary forage for many fish species. Transcriptional profiling of D. mitsukuri exposed to fish kairomone revealed that this cladoceran responds to predation risk through regulating activities of Wnt signalling, cuticle pattern formation, cell cycle regulation and anti-apoptosis pathways. Genes differentially expressed in response to predation risk are more likely to be members of expanded families. Our results suggest that expansions of multiple gene families associated with chemoreception and vision allow Daphnia to enhance detection of predation risk, and that expansions of those associated with detoxification and cuticle formation allow Daphnia to mount an efficient response to perceived predation risk. This study increases our understanding of the molecular basis of prey defences, being important evolutionary adaptations playing a stabilizing role in community dynamics.

The idea that hybridization promotes range expansion has received recent attention, but support from field studies is limited. We hypothesized that in the cladoceran waterflea genus Daphnia, parental species are geographically and ecologically separated, whereas hybrids occupy intermediate or occasionally extreme environments, potentially facilitating range expansion of parental species. We assessed the distribution of Daphnia dentifera, Daphnia galeata and their interspecific hybrids across 44 lakes in China (using mitochondrial and microsatellite markers), and related it to geographical and environmental lake descriptors. Parental species were geographically separated: D. dentifera occurred in western and central China, and D. galeata in eastern and central China, whereas hybrids were found in the western and central parts of the country. However, after controlling for geographical differences, the effect of environment on species distribution was strong and significant. Specifically, D. dentifera was present in high-altitude oligotrophic lakes, D. galeata in low-altitude eutrophic lakes and hybrids at intermediate to high altitudes, mainly in mesotrophic lakes. Microsatellite data indicated that hybrids were locally produced rather than having migrated from elsewhere; they probably resulted from encounters between expanding D. galeata and resident D. dentifera. The present study provides evidence that hybrids can survive in habitats that are otherwise suitable for only one of their parental species, emphasizing the importance of hybridization in expansion of species gene pools., (© 2019 John Wiley & Sons Ltd.)

Recent studies of the distribution and diversity of freshwater zooplankton have indicated that the previously understudied Eastern Palearctic region is an important biogeographic hotspot. Here, we explored the lineage diversity and reproductive modes of the Daphnia pulex species group across China. Members of this group are often keystone species of standing water bodies and are frequently used as a model system for ecological, evolutionary and, more recently, genomic studies. We found members of the D. pulex group in seven of seventy-six Chinese water bodies examined. We analyzed their phylogenetic position using mitochondrial markers, and explored the genetic structure of six populations using microsatellite markers. Mitochondrial DNA analysis suggested the presence of two distinct species complexes in China: the D. pulex complex that has a global distribution, and an apparently endemic Eastern Palearctic D. mitsukuri complex. Microsatellite analyses of six populations suggested that three of these reproduced by cyclical parthenogenesis, as evidenced by high clonal diversity and the absence of deviations from the Hardy-Weinberg equilibrium. In contrast, three other populations showed remarkably low diversity of multilocus genotypes. This suggests an obligate parthenogenetic reproductive mode, which was confirmed in one of the populations by comparison of genotypes of Daphnia adults and dormant embryos. All presumably obligate parthenogenetic clones were heterozygous at the majority of microsatellite loci, suggesting their hybrid origin. This was further supported by analyses of a small GTPase nuclear gene (rab4), as two alleles within single individuals belonged to different clades. Interestingly, one putatively obligate parthenogenetic clone carried three distinct alleles suggesting higher ploidy and potential gene flow between the D. pulicaria and D. mitsukuri complexes. Our data show that the expansion of the D. pulex complex in the Eastern Palearctic was associated with widespread hybridization., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: The zooplanktonic cladocerans Daphnia, present in a wide range of water bodies, are an important component of freshwater ecosystems. In contrast to their high dispersal capacity through diapausing eggs carried by waterfowl, Daphnia often exhibit strong population genetic differentiation. Here, to test for common patterns in the population genetic structure of a widespread Holarctic species, D. galeata, we genotyped two sets of populations collected from geographically distant areas: across 13 lakes in Eastern China and 14 lakes in Central Europe. The majority of these populations were genotyped at two types of markers: a mitochondrial gene (for 12S rRNA) and 15 nuclear microsatellite loci., Results: Mitochondrial DNA demonstrated relatively shallow divergence within D. galeata, with distinct haplotype compositions in the two study regions but one widely distributed haplotype shared between several of the Chinese as well as European populations. At microsatellite markers, clear separation was observed at both large (between China and Europe) and small (within Europe) geographical scales, as demonstrated by Factorial Correspondence Analyses, Bayesian assignment and a clustering method based on genetic distances. Genetic diversity was comparable between the sets of Chinese and European D. galeata populations for both types of markers. Interestingly, we observed a significant association between genetic distance and geographical distance for D. galeata populations in China but not in Europe., Conclusions: Our results indicate relatively recent spread of D. galeata across wide expanses of the Palaearctic, with one mtDNA lineage of D. galeata successfully establishing over large distances. Despite a clear differentiation of Chinese and European D. galeata at a nuclear level, the pattern of genetic variation is nevertheless similar between both regions. Overall, our findings provide insights into the genetic population structure of a cladoceran species with extremely wide geographical range.

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.

The effect of cyanobacterial blooms on aquatic ecosystems has received wide attention, yet little is known about their impacts on zooplankton genetic structure.For 26 months (April 2012–May 2014), we monitored zooplankton in a warm‐temperate ice‐free lake in Eastern China, with an emphasis on seasonal population dynamics of the cladoceran, Daphnia galeata. There was a seasonal succession in the zooplanktonic community (composed of Cladocera, Copepoda, and Rotifera).Genetic analysis (based on 14 microsatellite loci) of the 21 monthly samples in which D. galeata was present demonstrated that several clones could successfully overwinter and/or persist for many months. However, all clones, including these long‐lived clones, were completely replaced by new ones after October 2013, probably due to cyanobacteria blooms in that summer. A high clonal richness coupled with high turnover rate was observed in the D. galeata population overall, suggesting frequent sexual reproduction.Daphnia galeata experimentally fed with a diet of Microcystis aeruginosa (the most abundant toxic cyanobacterial species in the lake) had a substantially reduced survivorship, consistent with the field observations.Our findings highlight the changes of zooplanktonic population dynamics in terms of both community and clonal structure in a warm‐temperate ice‐free lake, and call for further investigation on ecological responses of zooplankton to cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]