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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.)

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]

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. [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]

The lake state and chemistry are sensitive to climate change at short timescales, but it is unclear how lake hydrochemistry responds to monsoonal climate, especially over glacial-interglacial cycles, owing to lack of well-dated and continuous sedimentary records. The types and geochemical compositions of authigenic carbonates from lacustrine sediments can be used to reconstruct past hydrochemistry. Yet, little is known about the significance and influencing factors of the Mg/Ca and Sr/Ca ratios of authigenic carbonates over glacial-interglacial cycles. Here, trace-element data of a 666 m long sediment sequence from the Heqing basin, a paleo-lake situated at the southeastern margin of the Tibetan Plateau, provide detailed glacial-interglacial hydrochemical conditions and their association with Indian summer monsoon (ISM) evolution during the entire Pleistocene. In interglacials, variation in both Mg/Ca and Sr/Ca ratios can serve as proxies for salinity as a result of precipitation of low-Mg calcite, constrained by enhanced ISM intensity and catchment weathering product. Instead, in glacials, high Mg/Ca and Sr/Ca ratios reflect high-Mg calcite and aragonite precipitation under low lake level conditions. There is a nonlinear response of the Sr/Ca ratio of lacustrine sediment to salinity variation when high-Mg calcite and aragonite precipitate in a hydrologically closed and evaporative lake. Based upon the sedimentary Sr/Ca and Mg/Ca ratios in the Heqing paleo-lake, the lake hydrochemistry during the Pleistocene experienced obvious glacial-interglacial ISM cycles at the life span of the lake itself: (1) in the old interval (2640–1840 ka), the salinity was low with cycles at the early stage of lake development owing to strong ISM; (2) in the middle interval (1840–920 ka), the lake was at a balance state and its salinity was more constrained by weathering solute, rather than ISM; and (3) in the young interval (920–130 ka), the salinity fluctuated with large amplitude over glacial-interglacial cycles and subsequent increase paced the weakened ISM. This study highlights the sensitivity of the types of lacustrine authigenic carbonates and lake chemistry to ISM changes over glacial-interglacial cycles. • In the monsoon-impacted areas, sedimentary Mg/Ca and Sr/Ca ratios controlled by ISM intensity and catchment weathering. • Mg/Ca ratios of lacustrine sediment reflect the types of authigenic carbonates over glacial-interglacial cycles. • Sr/Ca ratios of lacustrine sediment record salinity linearly in the interglacials, but nonlinearly in the glacials • Through time, lake hydrochemistry response to catchment weathering gradually decreased. [ABSTRACT FROM AUTHOR]