Introduction Microcystis aeruginosa, a dominant cyanobacterial species in freshwater blooms, produces toxins that pose serious threats to aquatic organisms and human health. However, the role of gut microbiota in mediating chironomid larval tolerance to cyanobacterial stress remains unclear.Methods This study investigated the physiological and gut microbial changes in Propsilocerus akamusi larvae exposed to M. aeruginosa at environmentally relevant densities commonly observed during cyanobacterial blooms (1.0 & times; 106 /107 /108 /109 cells L-1).Results The results showed that exposure to M. aeruginosa at 1.0 & times; 109 cells L-1 significantly suppressed chironomid larvae activity and led to high mortality, while the chironomid larvae exhibited certain tolerance at lower densities, with notably enhanced tolerance at 1.0 & times; 108 cells L-1, suggesting that this density may effectively trigger the tolerance mechanism of chironomid larvae to M. aeruginosa. High-throughput sequencing of 16S rRNA revealed a significant increase in the diversity of gut microbiota in chironomid larvae under lower densities of M. aeruginosa stress, especially 1.0 & times; 108 cells L-1. Combined with interaction network analysis, it was demonstrated that key bacterial genera (e.g., Cutibacterium, Epulopiscium, Methylobacterium and Sphaerotilus) associated with processes like toxin degradation, maintenance of intestinal homeostasis, and regulation of stress responses were significantly associated with tolerance of chironomid larvae to cyanobacterial stress, and there may be a synergistic effect among these key bacterial genera. Conversely, gasproducing, toxigenic, and pathogenic bacterial taxa (e.g., Carnobacterium, Clostridium and Aeromonas) increases were significantly correlated with the mortality of chironomid larvae under cyanobacterial stress. Furthermore, interactions between eukaryotic microorganisms (e.g., Opisthokonta and Alveolata) and Paucibacter may also participated in the regulation for chironomid larvae tolerance to M. aeruginosa.Discussion These findings provide new insights into the gut microbiome-mediated adaptive responses of benthic invertebrates to cyanobacterial blooms, and highlight the potential of keystone microbial taxa as ecological indicators or targets for microbiome-based management strategies in bloom-affected aquatic systems. This study also provide a data support for further mechanistic investigations into microbemediated host tolerance and the development of microbial-assisted ecological restoration approaches.

Increasing human activity and environmental changes have a complex impact on the evolutionary histories of most biomes. How environmental changes affect genetic evolution of wild populations has become a frequent research theme of biological ecology. Molecular techniques, in conjunction with palaeogenetics, facilitate understanding of the relationship between the genetic structure of wild populations and environmental change. In this study, genes encoding 16S rRNA, cytochrome c oxidase subunit 1 (COI), internal transcribed spacer (ITS), and Na+/K+ ATPase were used as molecular markers to reconstruct changes in the temporal population genetic structure of Daphnia sinensis based on the analysis of resting eggs from the sediment layers in Lake Chaohu. The genetic variation of the 16S rRNA, COI, ITS, and Na+/K+ ATPase genes of D. sinensis comprised 0–0.7

Mechanisms underlying the effects of ecological disturbance on aquatic ecosystems remain uncertain in subtropical regions. Here, we used a proxy-based approach to explore the community dynamics of testate amoebae (Arcellinida and Euglyphida) in two subtropical deep reservoirs (Tingxi and Shidou) in Xiamen, southeastern China, over a three-year period. Specifically, we employed drought and typhoon events recorded by weather station as proxies for ecological disturbance and chlorophyll-a estimated through fluorometry as a proxy for testate amoeba food. We addressed three questions: (1) Does typhoon-induced ecological disturbance affect the distribution patterns of testate amoebae in subtropical reservoirs? (2) Do typhoon- and drought-induced ecological disturbances affect the testate amoeba community across different water layers of subtropical reservoirs similarly? (3) Do stochastic or deterministic processes shaping the testate amoeba community over time exhibit similar patterns in different water layers of subtropical reservoirs? The typhoon-induced ecological disturbance resulted in pronounced shifts in the distribution patterns of testate amoebae, characterized by lower shell influx in surface waters (11-12 ind. mL(-1) d(-1)) and higher shell influx in middle and bottom waters (12-22 ind. mL(-1) d(-1)). The impact of typhoon-and drought-induced ecological disturbance was more pronounced in surface waters, and its pure explanation accounted for 29.5-35.5 % community variation in a variation partitioning analysis. The effect of stochastic processes revealed by the neutral model increased with water depths, accounting for 63.3-76.5 % of the community variation in the surface, 77.4-82.6 % in the middle, and 82.8-88.1 % in the bottom water. The effect of deterministic processes shown by the null model decreased with water depth and remained relatively low across all water layers. These results suggest contrasting patterns of assembly mechanisms underlying the testate amoeba community responses to ecological disturbance, with the balance perhaps shaped by water depth and the average water residence time in a reservoir.

Functional trait measures have the potential to represent local habitat conditions and are considered promising tools for biomonitoring and bioassessment programs. Macroinvertebrates are an ecologically significant group in freshwater ecosystems and possess a range of functional traits which are employed to assess ecological quality. Nevertheless, the relationships between macroinvertebrate functional structure and anthropogenic disturbances remain poorly understood. In this study, we conducted a comparison of how functional trait-based and taxonomy-based composition of macroinvertebrate assemblages responded to eutrophication in Lake Taihu, a typical large eutrophic freshwater lake in China. Specifically, we examined both the taxonomy-based and trait-based compositions of benthic macroinvertebrates varied along the eutrophication gradient. Eutrophication was associated with remarkable decreases in the abundance of gastropod taxa and increases in Oligochaeta and Chironomidae. Ten categories belonging to six traits were significantly different among three site groups. The eutrophic and transition sites showed higher abundance of Size2, burrowers, and integument-respiration organisms than macrophytic sites, whereas abundance of Size1, conical-shaped, sprawlers, scrapers, and lung-respiration were higher in macrophytic sites. Both taxonomic (36.8%) and functional compositions (39.8%) of macroinvertebrate assemblages were influenced by the same variables: COD Mn and transparency. Our study showed that macroinvertebrate trait-based approaches can be considered a useful supplement to traditional taxonomic approach for biomonitoring programs in freshwater lakes.

Freshwater lakes are subjected to increasing eutrophication and algal blooms worldwide, which have dramatically impacted the aquatic biodiversity. This situation is especially true in the Yangtze River Floodplain, China. However, few researches have been focused on differences in the spatial and temporal patterns of benthic macroinvertebrates assemblages between the two adjacent lakes in this floodplain. In this study, we conducted seasonal investigations in 2021 to compare the spatial and temporal patterns of macroinvertebrates in Lakes Taihu and Lake Chaohu. Non-metric multidimensional scaling (NMDS) analyses showed Lake Taihu was found to have differences in assemblages within the lake, but Lake Chaohu was found to have uniform assemblage across the entire lake. Macrophyte-dominated lake regions (eastern Lake Taihu) were characterised by the highest species richness and diversity indices than those in other lake regions. The pollution sensitive species (e.g. EPT: Ephemeroptera, Plecoptera and Trichoptera) were only distributed in the macrophytic areas of Lake Taihu. Corbicula fluminea, polychaetes Nephtys oligobranchia and Capitella sp. were dominant in the middle central lake regions in Lake Taihu. Lake Chaohu and the northern Lake Taihu, with turbid algal-dominated state, were characterised by dominance of Oligochaetes and Chironomids. These differences were attributed to varying habitats and environmental parameters among different lake regions. Canonical correspondence analysis (CCA) demonstrated that macrophytes, chemical oxygen demand (CODMn), temperature, ammonium (NH3-N) and electric conductivity (EC) were detected as important factors influencing such macroinvertebrate assemblage patterns between these two lakes. This study contributes to the scientific knowledge of within lake habitats, community assemblages, nutrients and pollution within these lakes.

High fish predation pressure can trigger "induced defense" in Daphnia species, resulting in phenotypic plasticity in morphology, behavior, or life-history traits. The molecular mechanisms of defense morphogenesis (e.g., the tail spine and helmet) in Daphnia remain unclear. In the present study, the tail spine, helmet, and body of Daphnia galeata under fish and non-fish kairomones conditions were collected for transcriptome analysis. A total of 24 candidate genes related to the morphological defense of D. galeata were identified, including 2 trypsin, one cuticle protein, 1 C1qDC protein, and 2 ferritin genes. The function of the Dagcut gene (D. galeata cuticle protein gene) in relation to tail spine morphology was assessed using RNA interference (RNAi). Compared with the EGFP (Enhanced green fluorescent protein) treatment, after RNAi, the expression levels of the Dagcut gene (D. galeata cuticle protein gene) showed a significant decrease. Correspondingly, the tail spines of the offspring produced by D. galeata after RNAi of the Dagcut gene appeared curved during the experiment. In whole-mount in situ hybridization, a clear signal site was detected on the tail spine of D. galeata before RNAi which disappeared after RNAi. Our results suggest that the Dagcut gene may play an important role in tail spine formation of D. galeata, and will provide a theoretical basis for studying the molecular mechanisms of the morphological plasticity in cladocera in the future.

It is well-established that environmental variability and cyanobacterial blooms have major effects on the assembly and functioning of bacterial communities in both marine and freshwater habitats. It remains unclear, however, how the ciliate community responds to such changes over the long-term, particularly in subtropical lake and reservoir ecosystems. We analysed 9-year planktonic ciliate data series from the surface water of two subtropical reservoirs to elucidate the role of cyanobacterial bloom and environmental variabilities on the ciliate temporal dynamics. We identified five distinct periods of cyanobacterial succession in both reservoirs. Using multiple time-scale analyses, we found that the interannual variability of ciliate communities was more strongly related to cyanobacterial blooms than to other environmental variables or to seasonality. Moreover, the percentage of species turnover across cyanobacterial bloom and non-bloom periods increased significantly with time over the 9-year period. Phylogenetic analyses further indicated that 84 %-86 % of ciliate community turnover was governed by stochastic dispersal limitation or undominated processes, suggesting that the ciliate communities in subtropical reservoirs were mainly controlled by neutral processes. However, short-term blooms increased the selection pressure and drove 30 %-53 % of the ciliate community turnover. We found that the ciliate community composition was influenced by environmental conditions with nutrients, cyanobacterial biomass and microzooplankton having direct and/or indirect significant effects on the ciliate taxonomic or functional community dynamics. Our results provide new insights into the long-term temporal dynamics of planktonic ciliate communities under cyanobacterial bloom disturbance.

BACKGROUND:In the life history of Daphnia, the reproductive mode of parthenogenesis and sexual reproduction alternate in aquatic ecosystem, which are often affected by environmental and genetic factors. Recently, the sex-biased genes are of great significance for clarifying the origin and evolution of reproductive transformation and the molecular regulation mechanism of sex determination in Daphnia. Although some genes on reproductive transition of Daphnia had been researched, molecular mechanism on the maintenance of sexually dimorphic phenotypes of Daphnia are still not well known, including differentially expressed genes in different life-history stages.RESULTS:In this study, four life-history stages of Daphnia sinensis, juvenile female (JF), parthenogenetic female (PF), sexual female (SF) and male (M), were performed for transcriptome, and male-biased genes were screened. A total of 110437 transcripts were obtained and assembled into 22996 unigenes. In the four life-history stages (JF, PF, SF and M), the number of unique unigenes is respectively 2863, 445, 437 and 586, and the number of common unigenes is 9708. The differentially expressed genes (DEGs) between male and other three female stages (M vs JF, M vs PF and M vs SF) were 4570, 4358 and 2855, respectively. GO gene enrichment analysis showed that the up-regulated genes in male were mainly enriched in hydrolase activity and peptidase activity. Thirty-six genes in male were significantly higher expression than in the three female stages, including one Doublesex (Dsx) gene, one laminin gene, five trypsin genes and one serine protease genes, and one chitin synthase gene and two chitinase genes.CONCLUSIONS:Our results showed that thirty-six candidate genes may be as the male-biased genes involving in the maintenance of sexually dimorphic phenotypes. This work will provide a reference for further exploring the functional genes related to sex differentiation in Daphnia species. Moreover, according to previous investigations, we thought that the expression level of functional genes may be related to the life-history stages of organisms, and may be also affected by different Daphnia species.

Global urbanization has resulted in local habitat fragmentation, influencing ecological processes and biodiversity conservation. However, little is known about the diversity and distribution of microbial communities across urban biotopes. Here, we compared testate amoeba communities in Moscow (63 samples from five urban parks) and Xiamen (69 samples from six urban parks) across four biotopes (tree hole, moss, soil, and sediment) to better understand microbial diversity and ecological processes shaping microbial communities. A total of 116 morphospecies (31 genera), corresponding to 90 in Moscow and 84 in Xiamen, were identified using light microscopy. The species richness per sample (mean ± standard error) was higher in Moscow parks (14 ± 1 species, n = 63) than Xiamen parks. The mean species richness per biotope was highest in the mosses (13 ± 1 species, n = 33). 13–26

Cyanobacterial dominance or blooms can influence ecosystem structure in reservoirs, yet there are only few studies of its effect on the resource use and trophic structure of zooplankton. We hypothesised that zooplankton traits would exhibit a strong response to the increase of invasive and toxic cyanobacteria. We investigated the effect of an invasive bloom-forming cyanobacterium Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii) on zooplankton functional traits (e.g., growth, reproduction, allochthonous resource use and realised niche) through laboratory experiments and 3-year field investigations in two subtropical reservoirs. The realised niche (i.e., resource and habitat use) was quantified using stable isotopes (termed isotopic niches). We fed the cladoceran zooplankton Moina sp. with Scenedesmus obliquus (chlorophyte), R. raciborskii, and a mixture of S. obliquus and R. raciborskii in laboratory experiments. A diet of R. raciborskii alone depressed the growth and reproduction of Moina sp. compared to a diet of S. obliquus alone, but a mixture of S. obliquus and R. raciborskii greatly alleviated the inhibition effects caused by cyanobacteria. Under natural field conditions, we did not find a strong inhibition effect of R. raciborskii dominance on the zooplankton, but a high biomass of R. raciborskii was associated with an increase (17%) in the relative allochthonous resource (terrestrially derived organic matter) use by cladocerans (but not for copepods), even though the chlorophyll-a concentration increased from 17 mu g/L in the non-bloom period to 28 mu g/L during periods of R. raciborskii dominance or blooms. Furthermore, a high biomass of R. raciborskii increased the contribution of inter-taxa variation (taxa sorting) to the expanded isotopic niches of the zooplankton community. Our study helps to clarify cyanobacteria-zooplankton interactions and highlights the importance of cyanobacterial dominance or blooms in regulating cross-ecosystem resource use and biogeochemical cycling mediated by zooplankton in aquatic ecosystems.

于2014年10-12月,采集厦门溪东水库浮游动物、浮游植物、浮游细菌与悬浮物样品,分析浮游动物群落与食物质量和食物浓度的关系,探讨桡足类营养级变化对浮游动物的影响.结果 表明,空间上后生浮游动物群落结构在水库不同水层间的差异不显著;时间上桡足类在水华期和非水华期的差异不显著,枝角类和轮虫在水华期和非水华期的差异显著.桡足类群落组成受食物质量的影响较大,枝角类群落组成受食物浓度的影响较显著,轮虫群落组成受食物质量和食物浓度的共同影响.进一步分析表明,食物质量和食物浓度与水温显著相关,枝角类生物量受食物浓度的影响,桡足类生物量与轮虫生物量呈显著相关.为了探究桡足类与食物质量的关系,我们以优势种舌状叶镖水蚤(Phyllodiaptomus tun-guidus)为对象分析化学计量特征,发现舌状叶镖水蚤体内的磷含量与水柱总磷平均浓度和水温呈显著正相关,其营养级变化范围为1.28～2.84,且营养级随着水温下降而显著增加.非水华期的食物磷含量增加可能是舌状叶镖水蚤丰度升高的原因之一,降温和种群繁殖的共同影响导致非水华期舌状叶镖水蚤体内磷含量逐渐下降,营养级增加.研究结果可为揭示浮游动物在富营养化内陆水体中的群落演变过程机制提供基础数据.

Testate amoebae are a diverse polyphyletic group of single-celled amoeboid protists in which the cytoplasm is enclosed within an external shell. They are widely distributed in various habitats including freshwater, brackish water, soil and moss. They play an important role in the biogeochemical cycles and energy flow of both aquatic and terrestrial ecosystems. They can provide a good record or proxy of past environmental change due to their environmental sensitivity and high diversity. Recent research on these microorganisms suggests they have been increasingly used as a biotic proxy of environmental and climatic reconstruction, water quality and pollution. Many testate amoeba species have a cosmopolitan distribution at least at the morphological level, but others have restricted geographical distribution. In China, we found there are abundant and diverse testate amoebae in reservoirs and lakes, including some endemic species. In recent years, however, the local species diversity of testate amoebae has been decreasing due to rapid increases in the level of reservoir or lake eutrophication. Currently, the conservation and sustainable use of biodiversity has become an important topic, so it is necessary and urgent to conduct systematic ecology research for endemic testate amoeba population in China. Netzelia tuberspinifera (basionym Difflugia tuberspinifera) is an endemic sensitive species of East Asia and is widely distributed in southern China. We found that the distribution of N. tuberspinifera was significantly related to latitude, elevation and temperature based on the datasets of 88 lakes and reservoirs in China, and this microorganism was mainly distributed in subtropical and tropical lakes and reservoirs characterized by low latitude, low elevation and high water temperature. Our study investigated the spatial-temporal distribution of N. tuberspinifera based on a high-frequency time series, sampled over four years from Tingxi Reservoir (Xiamen, China) combined with spatial samples from 28 reservoirs in 14 watersheds in southern China, and to reveal the ecological factors and processes that shape its distributions. The results showed that water temperature and foods (phytoplankton) exhibited significant effects on seasonal patterns of N. tuberspinifera population density (0-10.7 ind/L), with a higher correlation coefficient for water temperature than for food. In the Tingxi Reservoir, surface water temperature ranged from 14.3 to 32.1 degrees C over four years from 2016 to 2019. When water temperature was above 30 degrees C, N. tuberspinifera displayed better growth and reproduction, so its population density was higher in summer and autumn than in other seasons. On the spatial scale, the population density of N. tuberspinifera was 0-19.2 ind/L, which was mainly limited by geographical factors and decreased with an increase in latitude and longitude, respectively. Meanwhile, foods (phytoplankton), electrical conductivity and nitrate nitrogen also had significant effects on N. tuberspinifera population density. Interestingly, the variation in aperture diameter (33.5-68.2 mu m in Tingxi Reservoir; 33.5-73.6 mu m in 11 watersheds) of N. tuberspinifera was the major contributing factor in explaining the temporal-spatial differences of population morphological characteristics. Furthermore, we found that foods (phytoplankton) play a key role in the difference of aperture diameter between different seasons in Tingxi Reservoir. The difference in aperture diameter between the Yangtze River and other watersheds was mainly affected by foods (phytoplankton), total carbon and water turbidity. Based on the spatial-temporal difference of the N. tuberspinifera metapopulation, our work improves the understanding of geographical distribution and diversity of testate amoebae, and provides important references for ecological evaluation and biodiversity conservation in subtropical and tropical reservoirs.

With the effects of global warming becoming ever more obvious, biodiversity conservation is facing severe challenges. Currently, a deeper understanding the mechanisms of the effects of warming on sensitive species has become an important topic in aquatic biodiversity and ecological management. Our study first overcame the "challenge" for a sensitive indicator species (Netzelia tuberspinifera, an endemic testate amoeba species in East Asia) of culturing under laboratory conditions, and then explored its molecular response mechanisms to warming using transcriptomic analysis. Our data indicate that temperature mainly drove the geographical and seasonal variation of N. tuberspinifera populations. Transcriptomic results indicate that when the temperature is <25 °C, rising temperature triggers the biosynthesis of ribosomes; while the temperature is >25 °C, it triggers molecular processes related with cell division, test formation and general biomass increase. However, once the temperature exceeds 40 °C, N. tuberspinifera is unable to survive. Following from these results, the distribution of N. tuberspinifera might expand towards higher altitude or latitude regions under global warming. For the first time, our study showed direct evidence for sensitive protozoa species that presents a very narrow adaptation mechanism to local climate. Our work provides fundamental data for regional biodiversity conservation and scientific reference in subtropical and tropical waterbodies.

Testate amoebae are widely distributed in natural ecosystems and play an important role in the material cycle and energy flow. However, community assembly of testate amoebae is not well understood, especially with regard to the relative importance of the stochastic and deterministic processes over time. In this study, we used Illumina high-throughput sequencing to explore the community assembly of testate amoebae from surface waters in two reservoirs of subtropical China over a seven-year period. Majority of testate amoebae belonged to the rare taxa because their relative abundances were typically lower than 0.01% of the total eukaryotic plankton community. The testate amoeba community dynamics exhibited a stronger interannual than seasonal variation in both reservoirs. Further, species richness, rather than species turnover, accounted for the majority of community variation. Environmental variables explained less than 20% of the variation in community composition of testate amoebae, and the community assembly appeared to be strongly driven by stochastic processes. Based on the Sloan neutral community model, it was found that neutral processes explained more than 65% of community variation. More importantly, the Stegen null model analysis showed that the stochastic processes (e.g., ecological drift) explained a significantly higher percentage of community assembly than deterministic processes over seven years, although deterministic processes were more influential in certain years. Our results provide new perspectives for understanding the ecological patterns, processes and mechanisms of testate amoeba communities in freshwater ecosystems at temporal scale, and have important implications for monitoring plankton diversity and protecting drinking-water resources.

Difflugia australis, first described by Playfair (1918), has a unique morphotype. However, in the absence of morphometric data, it has not yet been reliably classified within the largest testate amoeba genus Difflugia. In this study D. australis collected from a subtropical reservoir in southeast China was investigated by means of light and scanning electron microscopy. Basing on biometrical data, we provide an improved diagnosis of this little known species. Difflugia australis is different from other similar congeners (i.e., D. bacillariarum Perty, 1849 and D. elegans Penard, 1890) mainly by the combination of the following features: the shell is broadly ovate, with rounded dome and convex sides converging down to a very short distance from the aperture and diverging suddenly into a short rim (collar). It is usually more or less asymmetrical, with one side being more dilated than the other. The shell surface is slightly smooth, composed of flat siliceous plates of irregular shape and size, mixed with fine grains; microbial spores of comparable forms are spread on the shell surface; particles are often interspersed with a network of organic cement with unique mesh pattern; one (sometimes two) slanting spine-like posterior end of the shell is variable in form; collar is mainly formed by small plates of equal size. The dimensions of the shell are: total shell length 88–106 µm; shell width 53–88 µm; aperture diameter 19–28 µm; collar height 3–6 µm; spine length 3‒23 μm. The size frequency distributions of both total shell length and shell width indicate that it is a size-monomorphic species with low variability.

Abstract Geographical patterns, climate, and environmental change have important influences on the distribution and spread of aquatic organisms. However, the relationships between the geographical pattern and phylogenetics of Daphnia as well as environmental change are not well known. The genetic diversity and phylogeography of seven D. similoides sinensis populations located in the middle and lower reaches of the Yangtze River were investigated based on the combination of mitochondrial (COI gene) and nuclear (14 microsatellite primers) markers. Based on the mitochondrial gene markers, D. similoides sinensis from the middle and lower reaches of the Yangtze River had one ancestral haplotype and two evolutionary clades. In addition, D. similoides sinensis population deviated from neutral evolution, showing signs of a bottleneck effect followed by population expansion. Based on the microsatellite markers, the seven D. similoides sinensis populations formed three main groups. The dendrogram (NJ/ME) showed that D. similoides sinensis based on the mitochondrial genes marker were obviously clustered two main clades, whereas there were three clades based on the microsatellite markers. Our results suggested that the habitat fragmentation due to the barrier of the dams and sluices promoted the genetic differentiation and phylogeography of D. similoides sinensis populations in the middle and lower reaches of the Yangtze River.

Understanding the effects of global warming on trait variation and trophic structure is a crucial challenge in the 21st century. However, there is a lack of general patterns that can be used to predict trait variation and community trophic structure under the ongoing environmental change. We investigated the responses of body size and community trophic structure of zooplankton to climate related factors (e.g., temperature). Isotopic niche breadth was applied to investigate the community trophic structure across a 1-year study from a subtropical reservoir (Tingxi Reservoir) in southeastern China. Body size and community isotopic niche breadth of zooplankton were larger during water mixing than stratification periods and correlated significantly with water temperature change along the time series. The contributions of intra- and intertaxonomic components to body size and community trophic structure variation showed significant relationships with the temperature change going from the mixing to stratification periods. Water temperature imposed direct effect on body size, while direct and indirect effect on the community trophic structure of zooplankton occurred through trophic redundancy along time series. Water temperature and community properties (e.g., body size, trophic redundancy, or trophic interaction) showed complex interactions and integrated to influence community trophic structure of zooplankton. Our results can expand the knowledge of how elevated temperature will alter individual trait and community trophic structure under future climate change.

Cladoceran remains (e.g., Daphnia ephippia) in sediments are usually able to accurately reflect the historical succession of cladoceran in lakes. However, mechanisms describing the interaction between density changes of empty ephippia and ephippia containing resting eggs in lake sediments and environmental factors remain unclear. The diversity and vertical changes of Daphnia ephippia in the 30-cm sedimentary layer (equivalent to about 90 years) were investigated in a subtropical Chinese lake, Lake Chaohu. The ephippia of D. similoides sinensis, D. pulex, and D. galeata were identified in the lake sediments. The densities and accumulation rates of both empty ephippia and ephippia containing resting eggs of three Daphnia species showed similar patterns. The values in the surface sedimentary layers (after the 1970s) were notably higher than in the bottom sedimentary layers (before the 1970s). The densities and accumulation rates of both empty ephippia and ephippia containing resting eggs of D. similoides sinensis were higher than those of D. pulex and D. galeata. Highly significant relationships (P < 0.001) between the TN contents and the ephippial densities and accumulation rates of D. similoides sinensis and D. galeata. TP contents had also significant correlations with the ephippial densities and accumulation rates of D. similoides sinensis and D. galeata, whereas it was not significant correlations with those of D. pulex (P > 0.05). Our results suggested that long-term eutrophication and cyanobacterial blooms might significantly affect the production of Daphnia ephippia and their vertical distribution in the sediments in eutrophic lakes.

Increased human activities and environmental changes may lead to genetic diversity variations of Cladocerans in water. Daphnia pulex are distributed throughout the world and often regarded as a model organism. The 16S rDNA, cytochrome c oxidase subunit I (COI), and 18S genes were used as molecular marks. The genetic diversity and phylogeny of D. pulex obtained from 10 water bodies in the middle and lower reaches of the Yangtze River were studied. For 16S rDNA, COI gene, and 18S gene, the A+ T content (65.4%, 58.4%, and 54.6%) was significantly higher than the G+ C content (34.6%, 41.6% and 45.4%). This result was consistent with higher A and T contents among invertebrates. Based on the genetic distances of 16S rDNA and COI genes, the genetic differences of D. pulex from 10 water bodies located in the middle and lower reaches of the Yangtze River in China was minimal (0%-0.8% for 16S rDNA and 0%-1.5% for COI gene). However, D. pulex evolved into two branches in the phylogenetic trees, which coincided with its geographical distribution. Compared with D. pulex from other countries, the average genetic distance of D. pulex obtained from 10 water bodies in the middle and lower reaches of the Yangtze River reached 9.1%-10.5%, thereby indicating that D. pulex may have evolved into different subspecies.