Genus Daphnia Research Articles

The Evolution of Extreme Genetic Variability in a Parasite-Resistance Complex.

Genomic regions that play a role in parasite defense are often found to be highly variable, with the MHC serving as an iconic example. Single nucleotide polymorphisms may represent only a small portion of this variability, with Indel polymorphisms and copy number variation further contributing. In extreme cases, haplotypes may no longer be recognized as orthologous. Understanding the evolution of such highly divergent regions is challenging because the most extreme variation is not visible using reference-assisted genomic approaches. Here we analyze the case of the Pasteuria Resistance Complex (PRC) in the crustacean Daphnia magna, a defense complex in the host against the common and virulent bacterium Pasteuria ramosa. Two haplotypes of this region have been previously described, with parts of it being non-homologous, and the region has been shown to be under balancing selection. Using pan-genome analysis and tree reconciliation methods to explore the evolution of the PRC and its characteristics within and between species of Daphnia and other Cladoceran species, our analysis revealed a remarkable diversity in this region even among host species, with many non-homologous hyper-divergent-haplotypes. The PRC is characterized by extensive duplication and losses of Fucosyltransferase (FuT) and Galactosyltransferase (GalT) genes that are believed to play a role in parasite defense. The PRC region can be traced back to common ancestors over 250 million years. The unique combination of an ancient resistance complex and a dynamic, hyper-divergent genomic environment presents a fascinating opportunity to investigate the role of such regions in the evolution and long-term maintenance of resistance polymorphisms. Our findings offer valuable insights into the evolutionary forces shaping disease resistance and adaptation, not only in the genus Daphnia, but potentially across the entire Cladocera class.

Temperature and light timing effects on diapause progression in Daphnia magna

Abstract Diapause is a survival strategy for freshwater crustaceans in the genus Daphnia that involves a genetically encoded inhibition of organism growth, development and reproduction. While the environmental triggers for Daphnia to produce diapause‐destined embryos and those that induce hatching are well documented, the influence of environmental challenges during different diapause sub‐phases remains unexplored. In this study, we exposed diapause‐destined embryos of Daphnia magna to different temperatures and light conditions during designated diapause sub‐phases. Our results underscore the importance of the maternal environment for the embryos that are in preparation for diapause. Moreover, we demonstrate a period of obligate developmental arrest during which reinitiation of development cannot be triggered. Additionally, we illustrate the embryos' ability to adjust hatching in response to environmental changes during the hatching process. This study reveals the inherent developmental pattern in Daphnia embryos as they progress through diapause and their adaptability to environmental changes.

Effects of dissolved organic matter on the toxicity of micro- and nanoplastic particles to Daphnia - a meta-analysis

Effects of micro- and nanoplastic particles (MNP) on organisms have been increasingly reported in recent years, with a large number of studies conducted on water fleas of the genus Daphnia. Most of the available studies used pristine particles that have not been exposed to the environment or to organic substances. In natural environments, however, organic substances like dissolved organic matter (DOM) attach to the MNP, forming an ecocorona on the particles’ surface. How the formation of an ecocorona influences MNP toxicity is still uncertain. While some studies suggest that DOM can mitigate the negative effects of MNP on organisms, other studies did not find such associations. In addition, it is unclear whether the DOM attached to the particles’ surface attenuates the effects of MNP directly or whether co-exposure with DOM solved in the medium attenuates MNP toxicity indirectly, for instance by increasing Daphnia‘s resilience to stressors in general. To draw more solid conclusions about the direction and size of the mediating effect of DOM on MNP-associated immobilization in Daphnia spp., we synthesized evidence from the published literature and compiled 305 data points from 13 independent studies. The results of our meta-analysis show that the toxic effects of MNP are likely reduced in the presence of certain types of DOM in the exposure media. We found similar mediating effects when MNP were incubated in media containing DOM before the exposure experiments, although to a lesser extent. Future studies designed to disentangle the effects of DOM attached to the MNP from the general effects of DOM in the exposure medium will contribute to a deeper mechanistic understanding of MNP toxicity in nature and enhance the reliability of MNP risk assessment.Graphical

RNA-seq analysis reveals changes in mRNA expression during development in Daphnia mitsukuri

Temporal transcriptional variation is a major contributor to functional evolution and the developmental process. Parthenogenetic water fleas of the genus Daphnia (Cladocera) provide an ideal model to characterize gene expression patterns across distinct developmental stages. Herein, we report RNA-seq data for female Daphnia mitsukuri at three developmental stages: the embryo, juvenile (three timepoints) and adult. Comparisons of gene expression patterns among these three developmental stages and weighted gene co-expression network analysis based on expression data across developmental stages identified sets of genes underpinning each of the developmental stages of D. mitsukuri. Specifically, highly expressed genes (HEGs) at the embryonic developmental stage were associated with cell proliferation, ensuring the necessary foundation for subsequent development; HEGs at the juvenile stages were associated with chemosensory perception, visual perception and neurotransmission, allowing individuals to enhance detection of potential environmental risks; HEGs at the adult stage were associated with antioxidative defensive systems, enabling adults to mount an efficient response to perceived environmental risks. Additionally, we found a significant overlap between expanded gene families of Daphnia species and HEGs at the juvenile stages, and these genes were associated with visual perception and neurotransmission. Our work provides a resource of developmental transcriptomes, and comparative analyses that characterize gene expression dynamics throughout development of Daphnia.

Attachment and Release of Water Fleas' Ephippia on a Medium-Sized Waterfowl's Leg for Migration.

Planktonic crustaceans of the genus Daphnia live in aquatic environments. Although they lack walking and flying capabilities, they have developed adaptations that facilitate the dispersal of their dormant forms, ephippia, to cross terrestrial barriers and reach neighborhood water bodies. It increases the survival rate of their species. It is reported that one of the ways this spread occurs is the transport of their ephippia through waterfowls' legs. Yet, little is known about how these ephippia are initially attached to the waterfowls' legs. In this work, using the legs of American Pekin ducks as test samples, we found that a "coating" mechanism might play a significant role in this attachment and that surface tension-induced attraction might have a secondary effect on it. Furthermore, we demonstrated that, no matter whether a duck's leg was inserted into water at a high or low speed, an ephippium could be released from the leg.

RNA-seq analysis to identify genes related to resting egg production of panarctic Daphnia pulex

BackgroundThe genus Daphnia switches its reproductive mode from subitaneous egg production to resting egg production in response to environmental stimuli. Although this life history trait is essential for surviving unsuitable environments, the molecular mechanism of resting egg production is little understood. In this study, we examined genes related to induction of resting egg production using two genotypes of panarctic Daphnia pulex, the JPN1 and JPN2 lineages, which differ genetically in the frequency of resting egg production. We reared these genotypes under high and low food levels. At the high food level, individuals of both genotypes continually produced subitaneous eggs, whereas at the low food level, only the JPN2 genotype produced resting eggs. Then, we performed RNA-seq analysis on specimens of three instars, including before and after egg production.ResultsThese results showed that expressed genes differed significantly between individuals grown under high and low food levels and among individuals of different instars and genotypes. Among these differentially expressed genes (DEGs), we found 16 that changed expression level before resting egg production. Some of these genes showed high-level expression only before resting egg production and one gene was an ortholog of bubblegum (bgm), which is reportedly up-regulated before diapause in bumblebees. According to gene ontology (GO) enrichment analysis, one GO term annotated as long-chain fatty acid biosynthetic process was enriched among these 16 genes. In addition, GO terms related to glycometabolism were enriched among down-regulated genes of individuals holding resting eggs, compared to those before resting egg production.ConclusionsWe found candidate genes highly expressed only before resting egg production. Although functions of candidate genes found in this study have not been reported previously in Daphnia, catabolism of long-chain fatty acids and metabolism of glycerates are related to diapause in other organisms. Thus, it is highly probable that candidate genes identified in this study are related to the molecular mechanism regulating resting egg production in Daphnia.

Multiclonal study of Daphnia magna with respect to adaptation to toxic cyanobacteria

AbstractMass developments of toxic cyanobacteria have increased in frequency due to global warming and eutrophication. Such cyanobacterial blooms impact whole freshwater ecosystems, especially reducing the abundance of herbivory species of the genus Daphnia. These negative effects on Daphnia have frequently been attributed to cyanobacterial secondary metabolites, among them hepatotoxic microcystins and protease inhibitors. Protease inhibitors inhibit major digestive proteases in the gut of Daphnia which results in reduced fitness, that is, population growth. To date evidence for local adaptation of Daphnia to cyanobacteria is confined to microcystin‐producing cyanobacteria and based on comparison of individual clones from different populations but lacks evidence from multiclone microcosm experiments. In the present study, D. magna clones from a Swedish lake where they coexist with the microcystin‐free Microcystis sp. strain BM25 were compared to clones from a Polish population without cyanobacteria, first in single‐clone experiments and subsequently in a multiclonal experimental population. The Swedish clones were assumed to be locally adapted to this protease inhibitor‐producing cyanobacterium and indeed showed higher population growth rates, a proxy for fitness, and dominated the population in the presence of dietary Microcystis sp. BM25, but not in the absence of this cyanobacterium. The results indicate an adaptive tolerance of the Swedish population and point at local adaptation to locally co‐occurring protease inhibitor‐producing cyanobacteria.

The Caucasus origin of daphnia species by means of phylogeny and functionality

Species of the genus Daphnia Mueller, 1785, are ancient aquatic organisms with origins dating back to approximately 145 million years. Over time, geographical, ecological, and behavioral barriers have led to the diversification of these species. The mechanism of Daphnia survival and dispersal is predetermined by the capability of their ephippium-protected embryos to remain dormant for extended periods of time, thus facilitating their widespread dispersal by wind, water currents, and animal vectors. This paper presents the analysis of the Daphnia species diversity in the Caucasus region, specifically Georgia, conducted using mitochondrial 16S rDNA and cytochrome oxidase subunit I (COI) gene fragments. The phylogenetic analysis reveals distinct evolutionary lineages among Daphnia species, molecular clock estimates suggesting the early Miocene divergence pattern, followed by the glaciation events of the Pleistocene and the uplift of the Caucasus mountains. This research highlights the challenges that species-level identification represents, emphasizing the necessity for using multiple gene fragments for accurate identification. The findings provide unprecedented insights into the evolutionary history, dispersal mechanisms, and genetic identification of Daphnia species in the Caucasus region. These results contribute to the comprehensive understanding of the ecological role and adaptive strategies of Daphnia, with implications for biodiversity conservation and environmental monitoring in aquatic ecosystems.

The effect of microplastics on the interspecific competition of Daphnia

Microplastic pollution is currently one of the most intensely studied ecological issues. Numerous studies have estimated the distribution and concentration of microplastics in various environments and determine how they affect their inhabitants. Much less effort has been place on assessing the possible effects of microplastics on interactions between organisms, including interspecific competition. Our aim was to test the hypothesis that the presence of microplastics affects the proportion of individuals of coexisting species and the elimination rate of the inferior competitor. The hypothesis was tested in competitive experiments done in the absence and presence of spherical non-biodegradable polystyrene and polyethylene and biodegradable polyhydroxybutyrate in environmentally relevant densities. In each of the experiments, we used three different pairs of closely related planktonic species of the genus Daphnia composed of the superior and inferior competitor: D. pulex and D. magna, D. magna and D. galeata, D. pulex and D. galeata. The results support our hypothesis and demonstrate each microplastic type had a different effect on the density of the competing species. The presence of polystyrene and polyethylene lowered the density of the superior competitor in each of the three pairs, at least partially due to a reduction in the number of gravid females, but not their fecundity. The presence of the polyhydroxybutyrate, in turn, increased the population density of D. magna in the variants with each of the two remaining species. Moreover, the presence of microplastics affected the elimination rate of the inferior competitor, i.e. polystyrene expedited the exclusion of D. magna by D. pulex, and polyhydroxybutyrate hampered the exclusion of D. magna by D. pulex. Our results suggest that long-term exposure to environmentally relevant densities of both non-biodegradable and biodegradable microplastics may affect the relative abundance of co-occurring species in zooplankton communities, and thus the functioning of aquatic ecosystems.

A new redescription of Daphnia pusilla (Serventy, 1929) (Cladocera: Daphniidae) with emphasis on the thoracic limbs of Daphnia (Ctenodaphnia) Dybowski amp; Grochowski, 1895.

The genus Daphnia O.F. Mller, 1776 (Crustacea: Cladocera) still has a confused taxonomy for several objective and subjective reasons. Still there are many taxa with inadequately described morphology, primarily among the subgenus Daphnia (Ctenodaphnia) Dybowski Grochowski, 1895. We provide a redescription of an Australian endemic taxon Daphnia (Ctenodaphnia) pusilla (Serventy, 1929) according to recent standards of morphological study with special attention to the thoracic limbs. We conclude that main differences between thoracic limbs of the subgenera D. (Ctenodaphnia) and Daphnia s. str. concern the limb I only as it is well-known among the cladocerans of other families. But still only a few species of D. (Ctenodaphnia) have been studied adequately, and efforts to redescribe their morphology need to be continued.

One Kairomone and Multiple Effects in Daphnia Species—5α-Cyprinol Sulfate Induces Morphological Defenses in the Invasive Species Daphnia lumholtzi

Recently, the first chemical cues, which induce defenses in freshwater zooplankton of the genus Daphnia have been identified. Still it is unknown how general these so-called kairomones are and if they are perceived by and thereby benefitting invasive species. We here report the chemical identity of the fish-derived chemical signal that induces morphological defensive structures in the invasive species Daphnia lumholtzi. We used bioassay-guided isolation (LC-MS) of incubation water of fish and identified the bile salt 5α-cyprinol sulfate (5α-CPS) as the kairomone. We confirmed this finding by bioassays, in which D. lumholtzi was exposed to purified 5α-CPS sulfate from fish bile and showed that 10 pM 5α-CPS induces significantly elongated helmets and spines in relation to body length. These results identify on one hand another Daphnia species besides Daphnia magna, which is responding to this particular fish-borne kairomone, and on the other hand they reveal another defense that the kairomone induces besides diel vertical migration (DVM). Taken together a high evolutionary conservancy of the molecular mechanism behind inducible defenses in Daphnia spp. against fish can be deduced. It is reasonable to expect that 5α-CPS is involved in further predator—prey communication between Daphnia and fish, which may be of special ecological relevance with regard to invasive species as D. lumholtzi.

More Light Please: Daphnia Benefit From Light Pollution by Increased Tolerance Toward Cyanobacterial Chymotrypsin Inhibitors

Cryptochromes are evolutionary ancient blue-light photoreceptors that are part of the circadian clock in the nervous system of many organisms. Cryptochromes transfer information of the predominant light regime to the clock which results in the fast adjustment to photoperiod. Therefore, the clock is sensitive to light changes and can be affected by anthropogenic Artificial Light At Night (ALAN). This in turn has consequences for clock associated behavioral processes, e.g., diel vertical migration (DVM) of zooplankton. In freshwater ecosystems, the zooplankton genus Daphnia performs DVM in order to escape optically hunting predators and to avoid UV light. Concomitantly, Daphnia experience circadian changes in food-supply during DVM. Daphnia play the keystone role in the carbon-transfer to the next trophic level. Therefore, the whole ecosystem is affected during the occurrence of cyanobacteria blooms as cyanobacteria reduce food quality due to their production of digestive inhibitors (e.g., protease inhibitors). In other organisms, digestion is linked to the circadian clock. If this is also the case for Daphnia, the expression of protease genes should show a rhythmic expression following circadian expression of clock genes (e.g., cryptochrome 2). We tested this hypothesis and demonstrated that gene expression of the clock and of proteases was affected by ALAN. Contrary to our expectations, the activity of one type of proteases (chymotrypsins) was increased by ALAN. This indicates that higher protease activity might improve the diet utilization. Therefore, we treated D. magna with a chymotrypsin-inhibitor producing cyanobacterium and found that ALAN actually led to an increase in Daphnia’s growth rate in comparison to growth on the same cyanobacterium in control light conditions. We conclude that this increased tolerance to protease inhibitors putatively enables Daphnia populations to better control cyanobacterial blooms that produce chymotrypsin inhibitors in the Anthropocene, which is defined by light pollution and by an increase of cyanobacterial blooms due to eutrophication.

Molecular data attest to the occurrence of autochthonous Daphnia pulex (Crustacea, Branchiopoda) populations in Sicily, Italy

Biological invasions are known to be among the most important threats to the long-term conservation of native biota, and their effects might be even more difficult to contrast when they are cryptic, i.e., when the non-native invaders cannot be easily recognised based on morphology, and can thus be confused with native taxa. Such cryptic invasions are known to widely occur in the cladoceran genus Daphnia O.F. Müller, 1785, so that the actual distribution and status of most species and lineages need to be checked with a genetic approach. In the frame of this work, we investigated if the Sicilian populations of D. (Daphnia) pulex Leydig, 1860 belonged to the allochthonous North American lineage, which is known to occur in several regions of the Palearctic and Afrotropical biogeographical regions, or rather to the autochthonous European lineage of the species. The molecular results obtained, based on a fragment of the mitochondrial gene encoding for NADH subunit dehydrogenase 5 (ND5), allowed us to rule out the allochthonous status of the species, confirming the presence of autochthonous relictual lineages of D. pulex in Sicily. The native status of these populations is in agreement with their local distribution, limited to natural and poorly-impacted water bodies mostly located in wooded areas at medium and high altitudes. The current local distribution of D. pulex in Sicily is possibly linked to the end of the last glacial maximum and the onset of warmer climatic conditions in the early Holocene, which led the species to take refuge in colder microthermal refugia located at high altitudes, determining their current relictual distribution.

Hybridization Dynamics and Extensive Introgression in the Daphnia longispina Species Complex: New Insights from a High-Quality Daphnia galeata Reference Genome.

Hybridization and introgression are recognized as an important source of variation that influence adaptive processes; both phenomena are frequent in the genus Daphnia, a keystone zooplankton taxon in freshwater ecosystems that comprises several species complexes. To investigate genome-wide consequences of introgression between species, we provide here the first high-quality genome assembly for a member of the Daphnia longispina species complex, Daphnia galeata. We further resequenced 49 whole genomes of three species of the complex and their interspecific hybrids both from genotypes sampled in the water column and from single resting eggs extracted from sediment cores. Populations from habitats with diverse ecological conditions offered an opportunity to study the dynamics of hybridization linked to ecological changes and revealed a high prevalence of hybrids. Using phylogenetic and population genomic approaches, we provide first insights into the intra- and interspecific genome-wide variability in this species complex and identify regions of high divergence. Finally, we assess the length of ancestry tracts in hybrids to characterize introgression patterns across the genome. Our analyses uncover a complex history of hybridization and introgression reflecting multiple generations of hybridization and backcrossing in the Daphnia longispina species complex. Overall, this study and the new resources presented here pave the way for a better understanding of ancient and contemporary gene flow in the species complex and facilitate future studies on resting egg banks accumulating in lake sediment.

Effect of Alginite on Some Antioxidant Indexes in Extracts of Two Variants of Mentha and Their Toxicity

The experimental work aimed to determine the effect of different applications of alginite on some antioxidant indexes in the extracts of the Mentha x piperita L. (cultivars Strawberry Mint and Chocolate Mint), and the acute toxicity of water extracts of the studied mint plants to freshwater invertebrates of the genus Daphnia sp. The content of total polyphenols, phenolic acids, and antioxidant activity were determined by spectrophotometric methods. The OECD manual No. 202 was used for the determination of EC50 48h in the water extracts of both variants of mint. The content of total polyphenols in all groups of the cv. Chocolate Mint ranged from 3.05 to 3.37 mg CAE/100 g DW. On the other hand, the significantly lower (p < 0.001) content of total polyphenols (from 1.01 to 1.38 mg CAE/100 g DW) was found in all groups with the cv. Strawberry Mint. The antioxidant activity determined by the DPPH method was from 115.7 to 119.5 mg TAEC/100 g DW in the cv. Chocolate Mint, but was 2 times lower (from 48.8 to 65.7 mg TAEC/100 g DW) in the cv. Strawberry Mint. The content of phenolic acids in the cv. Chocolate Mint was significantly higher (but only 1.1-fold), than in the cv. Strawberry Mint. The mean acute toxicity after 48 h exposure of the cv. Chocolate Mint to daphnids was nearly 40 times higher than the mean acute toxicity of the cv. Strawberry Mint (EC50 0.25 mg/L vs. EC50 9.62 mg/L, respectively). We can conclude, that the cv. Chocolate Mint is a more potent source of substances with antioxidant properties, such as polyphenols and phenolic acids, which is reflected in the significantly increased DPPH radical scavenging activity as compared to the cv. Strawberry Mint. We can only speculate that the higher amounts of the aforementioned active substances in the cv. Chocolate Mint were associated with an increased level of acute toxicity to the tested water invertebrates as compared to the cv. Strawberry Mint. The impacts of alginite application on all studied antioxidant indexes as well on the acute toxicity of the extracts of both variants of mint were not confirmed.

Pricklier with the proper predator? Predator-induced small-scale changes of spinescence in Daphnia.

Phenotypic plasticity in defensive traits is a common response of prey organisms to variable and unpredictable predation regimes and risks. Cladocerans of the genus Daphnia are keystone species in the food web of lentic freshwater bodies and are well known for their ability to express a large variety of inducible morphological defenses in response to invertebrate and vertebrate predator kairomones. The developed defenses render the daphnids less susceptible to predation. So far, primarily large‐scale morphological defenses, like helmets, crests, and tail‐spines, have been documented. However, less is known on whether the tiny spinules, rather inconspicuous traits which cover many Daphnia’s dorsal and ventral carapace margins, respond to predator kairomones, as well. For this reason, we investigated two Daphnia species (D. magna and D. longicephala) concerning their predator kairomone‐induced changes in dorsal and ventral spinules. Since these small, inconspicuous traits may only act as a defense against predatory invertebrates, with fine‐structured catching apparatuses, and not against vertebrate predators, we exposed them to both, an invertebrate (Triops cancriformis or Notontecta maculata) and a vertebrate predator (Leucaspius delineatus). Our results show that the length of these spinules as well as spinules‐covered areas vary, likely depending on the predator the prey is exposed to. We further present first indications of a Daphnia species‐specific elongation of the spinules and an increase of the spinules‐bearing areas. Although we cannot exclude that spinescence is altered because it is developmentally connected to changes in body shape in general, our results suggest that the inducible alterations to the spinule length and spinules‐covered areas disclose another level of predator‐induced changes in two common Daphnia species. The predator‐induced changes on this level together with the large‐scale and ultrastructural defensive traits may act as the overall morphological defense, adjusted to specific predator regimes in nature.

Thwarting predators? A three-dimensional perspective of morphological alterations in the freshwater crustacean Daphnia.

Predation is a major selective agent, so that many taxa evolved phenotypically plastic defensive mechanisms. Among them are many species of the microcrustacean genus Daphnia, which respond to an increased predation risk by developing inducible morphological alterations. Some of these features are obvious and easily recognized, e.g., crests in D. longicephala, while others are rather hidden, such as the bulkier shape of D. magna induced by the presence of the tadpole shrimp Triops. In this study we investigated the extraordinary diversity of morphological adaptations in the presence of predators with different foraging strategies in six predator-prey systems. For the first time we were able to analyze the unexposed and predator-exposed morphs comprehensively using three-dimensional scanning and reconstruction. We show that morphological changes are manifold in appearance between species and predators, and go beyond what has been known from previous 2D analyses. This further demonstrates the enormous trait flexibility of Daphnia. Interestingly, we found that among this variety some species share morphological strategies to counter a predator, while others use a different strategy against the same predator. Based on these intra- and interspecific comparisons, we discuss the mechanisms by which the respective defense might operate. These data therefore contribute to a deeper understanding of the inducible defenses’ morphology as well as their diversified modes of operation in Daphnia, being a cornerstone for subsequent investigations, including the determination of costs associated with morphological change.

Limnoecosystems of the Kurgan region with domination in the zooplankton of the species group Daphnia (Daphnia)

The paper presents data on the state of populations of species of the genus Daphnia in the ecosystems of small lakes in the forest-steppe zone of the south-west of Western Siberia, in which they are the highest trophic link. The research was conducted in 2017 on the territory of the Kurgan region. In total, 5 lakes (Lysanovo, Dolgoe, Golovka, Second Mogilnoye, Krutoyar) located between 66°30’ and 67°00 ‘ were studied.d. and 55°00’ and 55°30 ‘ s. The studied lakes are typical for the forest-steppe zone of Western Siberia. According to the chemical composition, the lake waters of the studied limnoecosystems can be attributed to the bicarbonate and chloride classes, the sodium group. 5 species of the genus Daphnia were found in the reservoirs: Daphnia (Daphnia) - D.(D.) pulex, D.(D.) obtusa, D.(D.) longispina, D.(D.) galeata, and Daphnia (Ctenodaphnia)- D. (C.) magna. Populations of D. (D.) pulex are found in all the studied reservoirs. The maximum density and biomass of crustaceans of this species is noted in Lake Mogilnoye of 51 thousand individuals/m² and 3.62 g/m², respectively. The minimum, in the lake Dolgoe – 3.8 thousand individuals/m² and 0.019 g/m². Of the other species, D. (C.) magna is most common-in three reservoirs. At the same time, there is a significant variability in the population density from 0.478 thousand. individuals/m² (Lake Krutoyar) up to 9,864 thousand. individuals/ m² (lake Dolgoe). D. (D.) longispina is found in two lakes – the Golovka (25,230 thousand. individuals/m²) and Krutoyar (6,428 thous. individuals/m²). The lowest occurrence is typical for D. (D.) obtusa (Lake Golovka) and D. (D.) galeata (Lake Lysanovo). The greatest species diversity of the genus Daphnia was observed in Lake Golovka (3 species) and Krutoyar (3 species). It is concluded that the studied limnoecosystems are characteristic daphnia reservoirs with the dominance of one or two species from the genus Daphnia.

Dangerous connections: biochemical and behavioral traits in Daphnia magna and Daphnia longispina exposed to ecologically relevant amounts of paracetamol.

Exposure of nontarget organisms to therapeutic agents can cause distinct toxic effects, even at low concentrations. Paracetamol is a painkiller drug, widely used in human and veterinary therapies, being frequently found in the aquatic compartment in considerable amounts. Its toxicity has already been established for some species, but its full ecotoxicological potential is still not sufficiently described. To characterize the ecotoxicity of paracetamol, the present study evaluated several parameters, such as acute immobilization (EC50 calculation), biochemical alterations, and behavioral effects, in two species of freshwater microcrustaceans of the genus Daphnia (D. magna and D. longispina). To increase the relevance of the data obtained, animals were exposed to levels of paracetamol similar to those already reported to occur in the wild. Data showed antioxidant responses in both species, namely an increase of catalase and GSTs activities in D. magna. On the contrary, effects of paracetamol on D. longispina included only an impairment of GSTs activity. Despite the absence of anticholinesterasic effects, behavioral modifications were also observed. This set of data indicates that realistic levels of paracetamol may trigger the activation of the antioxidant defense system of freshwater crustaceans, causing changes in behavioral traits (increase in swimming time, but with a reduction in swimming distance) of unknown etiology that are likely to affect normal life traits of wild populations.

Sex Determination and Differentiation in Decapod and Cladoceran Crustaceans: An Overview of Endocrine Regulation.

Mechanisms underlying sex determination and differentiation in animals are known to encompass a diverse array of molecular clues. Recent innovations in high-throughput sequencing and mass spectrometry technologies have been widely applied in non-model organisms without reference genomes. Crustaceans are no exception. They are particularly diverse among the Arthropoda and contain a wide variety of commercially important fishery species such as shrimps, lobsters and crabs (Order Decapoda), and keystone species of aquatic ecosystems such as water fleas (Order Branchiopoda). In terms of decapod sex determination and differentiation, previous approaches have attempted to elucidate their molecular components, to establish mono-sex breeding technology. Here, we overview reports describing the physiological functions of sex hormones regulating masculinization and feminization, and gene discovery by transcriptomics in decapod species. Moreover, this review summarizes the recent progresses of studies on the juvenile hormone-driven sex determination system of the branchiopod genus Daphnia, and then compares sex determination and endocrine systems between decapods and branchiopods. This review provides not only substantial insights for aquaculture research, but also the opportunity to re-organize the current and future trends of this field.