Water Flea Daphnia Magna Research Articles

Lineage diversity, morphological and genetic divergence in Daphnia magna (Crustacea) among Chinese lakes at different altitudes

The biogeography and genetic structure of aquatic zooplankton populations remains understudied in the Eastern Palearctic, especially the Qinghai-Tibetan Plateau. Here, we explored the population-genetic diversity and structure of the cladoceran waterflea Daphnia magna found in eight (out of 303 investigated) waterbodies across China. The three Tibetan D. magna populations were detected within a small geographical area, suggesting these populations have expanded from refugia. We detected two divergent mitochondrial lineages of D. magna in China: one was restricted to the Qinghai-Tibetan Plateau and the other was present in lowland China. Several different haplotypes in the Qinghai-Tibetan Plateau were most similar to those from various parts of Siberia, suggesting that as a source region. We also found substantial genetic differentiation between D. magna populations from the Qinghai-Tibetan Plateau and those from lowland China. Moreover, significant morphological differences were identified: D. magna from the Qinghai-Tibetan Plateau had a larger head length, body length and body width than did those from lowland China. Geographical and environmental factors were correlated with the observed morphological variation and genetic divergence of D. magna in China. Our data offer an insight into the divergence of freshwater zooplankton due to the uplift of the Qinghai-Tibetan Plateau.

Complete mitochondrial genome of the freshwater water flea Daphnia magna NIES strain (Cladocera, Daphniidae): Rearrangement of two ribosomal RNA genes

The complete mitochondrial genome was sequenced from the NIES strain of the freshwater water flea Daphnia magna. The sequenced mitochondrial genome size of the NIES strain of D. magna was 17,432 bp, possessing identical gene order and the contents to those of the congeneric species Daphnia galeata in the genus Daphnia, but 16S and 12S rRNA genes was in opposite direction compared to other daphnid, while ND2 gene was also often found in opposite direction in the genus Daphnia. Overall, the mitochondrial genome of D. magna NIES strain has 13 protein-coding genes (PGCs), two rRNAs, and 22 tRNAs. Of 13 PGCs, four genes (CO1, CO2, ND5, and ND4) had incomplete stop codons. Furthermore, the stop codons of the remaining nine PGCs were TAG and TAA, while the start codons of CO1, ND6, and ND3 genes were ATT, ATT, and ATC, respectively. The base composition of D. magna NIES strain mitogenome shows an anti-G and –T bias (16.5% and 16.0%) on the L strand, respectively.

Population dynamics and life history traits of Daphnia magna across thermal regimes of environments

The consequences of raising temperatures have been intensively studied by biologists and ecologists for the past few decades. However, current climatic changes also include many anomalous weather events, such as intra-seasonal heatwaves followed by immediate decreases in temperature. In this study, the responses of population development and life history traits to different thermal regimes were investigated. The freshwater water flea Daphnia magna (Cladocera, Crustacea) was used as a model organism. Daphnia magna populations were monitored under temperature regimes of warm (25 °C), cold (5 °C), synchronous (gradual changes between 25 °C and 5 °C) or stochastic (random changes between 25 °C and 5 °C). Population size of D. magna populations decreased with unpredictability of thermal conditions; the highest density of D. magna was found in the warm environment and the lowest density in the stochastic environment. Thermal regime had significant impact on the prevalence of asexual and sexual reproduction of D. magna. Under a synchronous regime, an accumulation of asexual reproduction was observed during cold episodes; this was followed by a phase of population disturbance, manifesting itself in high fluctuations of asexual reproduction and a pattern of sexual reproduction typical of a cold regime. Under a stochastic regime, the population disturbances were observed throughout the duration of the experiment. Daily observations of individual life history traits revealed that the development of populations under different thermal regimes resulted from the regime-specific survivability of neonates. Population development was also affected by the frequency of reproduction, which consisted of the number of broods carried per lifetime. The results indicate that not only temperature but also shifts in thermal conditions have an important influence on individual life history traits and population dynamics of D. magna. It is important to consider the effects of shifts in water temperature on demographic and individual traits simultaneously because the impact of thermal changes on population traits can be modified by individual life histories.

Development and Efficiency Assessment of New Methods on Rapid Assessment of Toxicity in Environmental Monitoring

The transformation of hazardous pollutants in the environment usually results in formation of hard-to-identify compounds that may have a significant impact on ecosystems. They are difficult to identify by conventional methods of quantitative chemical analysis, but their detrimental effects can be detected by biological methods. The goal of this study was to develop novel methodological approaches to the express assessment of the state of the environment as well as toxicity of its components in the process of biological monitoring at hazardous industrial facilities. The article presents the results of comprehensive toxicity assessment of environmental objects using originally developed system of express methods. The objects of research were water fleas (Daphnia magna Straus and Ceriodaphnia affinis Lilljeborg), infusoria (Paramecium caudatum), preparation of lyophilized fluorescent bacteria based on recombinant Escherichia coli strain M-17 (Ecolum), algae (Chlorella vulgaris Beijer, Scenedesmus quadricauda (Turp.) Breb.), and mammalian gonads. The original methods for determining toxicity by changing the motor activity of water fleas at elevated temperatures of the studied environment are described. The description of the following original utility models is presented: “Method of bioassay for water samples and device for its implementation”, “Device for express assessment of natural environment quality” and “Device for comprehensive assessment of natural environment quality”, confirmed by the patents of the Russian Federation. Their use may significantly reduce the cost of ecotoxicological studies in terms of time and money expenditures. The effectiveness of the system of express methods was established during a biological monitoring of a sanitary protection zone of the Balakovo NPP. Toxicity of the samples of bottom sediments, soil, as well as water samples from the cooler pond and the adjacent water area of the Saratov reservoir were identified. The bioassay results were matched by both conventional methods’ results and originally developed system of express methods.

Alleviation of copper toxicity in Daphnia magna by hydrogen nanobubble water

As a novel antioxidant, hydrogen water has been widely used to alleviate oxidative stress in plants as well as in the medical field. However, the function of hydrogen water in environmental toxicology remains unknown. In this study, combining nanobubbles (NBs) and hydrogen water, we investigate the effect and mechanism of hydrogen NB water on copper induced acute toxicity to water fleas (Daphnia magna). The 24-h lethal Cu concentrations at which 50 % of the population die were 84 μg/L in hydrogen NB water and 45 μg/L in control water, confirming that hydrogen NB water effectively alleviated acute Cu toxicity in D. magna. The results were consistent with a significant reduction of Cu uptake and decrease of Cu accumulation in D. magna. As confirmed in fluorescence spectrophotometry and high-content screening system analysis, the hydrogen NB water also significantly reduced the oxidative damage and improved Cu tolerance in D. magna. From the results, it can be inferred that hydrogen NB water alleviates Cu stress in D. magna by depressing Cu bioaccumulation and reducing oxidative stress. The results provide basic data of hydrogen NB water for environmental toxicologists, and also a reference for the application of hydrogen NB water in the environment.

Effects of thermal evolution on the stoichiometric responses to nano-ZnO under warming are not general: insights from experimental evolution.

A key challenge for ecological risk assessment of contaminants under global warming is to predict effects at higher levels of biological organisation. One approach to reach this goal is to study how contaminants and warming cause changes in body stoichiometry as these may potentially cascade through food webs. Furthermore, though contaminants typically interact with warming, how rapid adaptation to higher temperatures affects these interactions is poorly studied. Here, we examined the effects of an important contaminant (ZnO nanoparticles, nZnO) and mild warming (4 °C) on body stoichiometry (C, N, P and their ratios) of an aquatic keystone species, the water flea Daphnia magna. To evaluate whether thermal evolution impacts the effects of nZnO at higher temperatures, we compared two sets of clones from a thermal selection experiment where Daphnia were kept in outdoor mesocosms at ambient or ambient +4 °C temperatures for 2 years. Exposure to nZnO decreased key body stoichiometric ratios (C:N, C:P and a trend for N:P) while warming increased the body C:N ratio. The stoichiometric changes to nZnO and warming were mostly independent and could be partly explained by changes in the macromolecules sugars and fat. Exposure to nZnO decreased C-rich sugars contributing to a reduced %C. Warming reduced body %C due to decreased C-rich sugars and fat levels, yet warming decreased body N% even more resulting in a higher C:N ratio. The stoichiometric responses to nZnO at the higher temperature did not differ between the two sets of clones, indicating experimental thermal evolution did not change the effects of nZnO under warming. Studying the stoichiometric responses to nZnO and warming of this keystone species may provide novel insights on the toxic effects of contaminants under warming. Moreover, understanding the influence of thermal evolution on the toxicity of contaminants is important for ecological risk assessment especially in a warming world.

The effects of 1-hexyl-3-methylimidazolium bromide on embryonic development and reproduction in Daphnia magna.

Ionic liquids (ILs) are acknowledged as green chemicals and favorable substitutes for volatile organic solvents, which are currently used. However, previous studies have shown that these compounds had toxicological impacts on aquatic organisms. To investigate the effects of 1-hexyl-3- methylimidazolium bromide ionic liquid ([C6mim]Br) on embryonic development and reproduction in water flea (Daphnia magna), a series of exposure experiments were conducted, including acute toxicity, maternal exposure, and chronic exposure tests. In acute toxicity experiment, D. magna neonates exhibited developmental abnormalities in the shell spine and the second antennae in a concentration-dependent manner after exposure to [C6mim]Br. The results in maternal exposure test also revealed a certain embryo-toxicity in response to [C6mim]Br in D. magna. However, the toxicity was lower than that conveyed by direct acute exposure, this indicated that the IL could act directly on organism. During the 21 days chronic exposure, the 1.6mg/L exposure caused marked drop in the survival, molts and the number of the first brood of D. magna. Meanwhile, the total number of offspring was significantly declined in 1.6mg/L concentration treatment groups, whereas increased in 0.2mg/L groups. Generally, abnormalities in the offspring were significantly increased across all of the treatment groups in contrast to the control. No effect on sex differentiation was found during the experiments. These findings suggested that [C6mim]Br could affect embryonic development and reproduction in D. magna, and provided references for further study on the mechanisms underlying toxicological effects of ILs and the assessment of their potential environmental risks.

Food availability modulates temperature-dependent effects on growth, reproduction, and survival in Daphnia magna.

Reduced body size and accelerated life cycle due to warming are considered major ecological responses to climate change with fitness costs at the individual level. Surprisingly, we know little about how relevant ecological factors can alter these life history trade‐offs and their consequences for individual fitness. Here, we show that food modulates temperature‐dependent effects on body size in the water flea Daphnia magna and interacts with temperature to affect life history parameters. We exposed 412 individuals to a factorial manipulation of food abundance and temperature, tracked each reproductive event, and took daily measurements of body size from each individual. High temperature caused a reduction in maximum body size in both food treatments, but this effect was mediated by food abundance, such that low food conditions resulted in a reduction of 20% in maximum body size, compared with a reduction of 4% under high food conditions. High temperature resulted in an accelerated life cycle, with pronounced fitness cost at low levels of food where only a few individuals produced a clutch. These results suggest that the mechanisms affecting the trade‐off between fast growth and final body size are food‐dependent, and that the combination of low levels of food and high temperature could potentially threaten viability of ectotherms.

Multilevel ecotoxicity assessment of environmentally relevant bisphenol F concentrations in Daphnia magna

With the pressure to ban or limit the use of Bisphenol A (BPA), substitutes such as bisphenol F (BPF) are applied to various commodities and generally detected in aquatic systems worldwide. To understand the potential ecological risk of BPF, the acute toxicity as well as behavioural, physiological and biochemical parameters of the water flea Daphnia magna were assessed. Following BPF exposure at concentrations ranging from 0.1 μg L−1 to 100 μg L−1, phenotypic traits including growth development, fecundity and swimming activity were significantly inhibited in response to exposure to sublethal concentrations (1–100 μg L−1) of BPF, which had a positive relationship with the activity of antioxidant enzymes. Moreover, the acetylcholinesterase (AChE) activity, which was strictly associated with the behavioural changes, was clearly inhibited, which was also obviously related to the heart rate and thoracic limb activity. Compared to the toxicity of BPA, BPF induces similar toxic effects, and the health concerns regarding the use of these alternatives should be highlighted.

Ecotoxicity of ammonium chlorophenoxyacetate derivatives towards aquatic organisms: Unexpected enhanced toxicity upon oxygen by sulfur replacement

Phenoxyacetate herbicides, such as 2,4-D and MCPA, having a high toxicity to non-target organisms are commonly used for controlling broadleaf weeds in agriculture. However, novel and environmentally friendly analogs are constantly sought after. For this purpose, various substituents at the phenyl group have been tested to find the optimal balance between the potent herbicidal activity and safety for non-target species. In this work, we investigated the influence of the oxygen by sulfur replacement in the phenoxy moiety of ammonium chlorophenoxyacetates on the toxicity towards aquatic organisms, such as bacteria (Vibrio fischeri), water flea (Daphnia magna) and freshwater fish (Pimephales promelas) by determining experimental (Microtox® test – V. fischeri) and predicted (ACD Lab Percepta software – D. magna, P. promelas) EC50/LC50 values. The achieved results showed that in contrary to the literature observations, where O-compounds were more toxic than their S-analogs (urea/thiourea), the O/S replacement in chlorophenoxyacetate significantly increased ecotoxicity of the S-analogs (up to 11 times). Moreover, one- and two-substituted phenoxyacetates in the form of ammonium salts were less toxic to V. fischeri than the commercially available phenoxy herbicides in the acid form. The logP/logD values were also calculated to understand hydro/lipophilic nature of the investigated compounds and differences in their toxicity.

Dissecting the genetic architecture of a stepwise infection process.

How a host fights infection depends on an ordered sequence of steps, beginning with attempts to prevent a pathogen from establishing an infection, through to steps that mitigate a pathogen's control of host resources or minimize the damage caused during infection. Yet empirically characterizing the genetic basis of these steps remains challenging. Although each step is likely to have a unique genetic and environmental signature, and may therefore respond to selection in different ways, events that occur earlier in the infection process can mask or overwhelm the contributions of subsequent steps. In this study, we dissect the genetic architecture of a stepwise infection process using a quantitative trait locus (QTL) mapping approach. We control for variation at the first line of defence against a bacterial pathogen and expose downstream genetic variability related to the host's ability to mitigate the damage pathogens cause. In our model, the water-flea Daphnia magna, we found a single major effect QTL, explaining 64% of the variance, that is linked to the host's ability to completely block pathogen entry by preventing their attachment to the host oesophagus; this is consistent with the detection of this locus in previous studies. In susceptible hosts allowing attachment, however, a further 23 QTLs, explaining between 5% and 16% of the variance, were mapped to traits related to the expression of disease. The general lack of pleiotropy and epistasis for traits related to the different stages of the infection process, together with the wide distribution of QTLs across the genome, highlights the modular nature of a host's defence portfolio, and the potential for each different step to evolve independently. We discuss how isolating the genetic basis of individual steps can help to resolve discussion over the genetic architecture of host resistance.

Epigenetic, transcriptional and phenotypic responses in two generations of Daphnia magna exposed to the DNA methylation inhibitor 5-azacytidine.

The water flea Daphnia magna is a keystone species in freshwater ecosystems and has been widely used as a model organism in environmental ecotoxicology. This aquatic crustacean is sensitive to environmental stressors and displays considerable plasticity in adapting to changing environmental conditions. Part of this plasticity may be due to epigenetic regulation of gene expression, including changes to DNA methylation and histone modifications. Because of the generally hypomethylated genome of this species, we hypothesized that the histone code may have an essential role in the epigenetic control and that histone modifications might be an early marker for stress. This study aims to characterize the epigenetic, transcriptional and phenotypic responses and their causal linkages in directly exposed adult (F0) Daphnia and peritoneal exposed neonates (F1) after a chronic (7-day) exposure to a sublethal concentration (10 mg/l) of 5-azacytidine, a well-studied vertebrate DNA methylation inhibitor. Exposure of the F0 generation significantly reduced the cumulative fecundity, accompanied with differential expression of genes in the one-carbon-cycle metabolic pathway. In the epigenome of the F0 generation, a decrease in global DNA methylation, but no significant changes on H3K4me3 or H3K27me3, were observed. In the F1 offspring generation, changes in gene expression, a significant reduction in global DNA methylation and changes in histone modifications were identified. The results indicate that exposure during adulthood may result in more pronounced effects on early development in the offspring generation, though interpretation of the data should be carefully done since both the exposure regime and developmental period is different in the two generations examined. The obtained results improve our understanding of crustacean epigenetics and the tools developed may promote use of epigenetic markers in hazard assessment of environmental stressors.

Analysing the evolutional and functional differentiation of four types of Daphnia magna cryptochrome in Drosophila circadian clock

Cryptochrome (CRY) plays an important role in the input of circadian clocks in various species, but gene copies in each species are evolutionarily divergent. Type I CRYs function as a photoreceptor molecule in the central clock, whereas type II CRYs directly regulate the transcriptional activity of clock proteins. Functions of other types of animal CRYs in the molecular clock remain unknown. The water flea Daphnia magna contains four Cry genes. However, it is still difficult to analyse these four genes. In this study, we took advantage of powerful genetic resources available from Drosophila to investigate evolutionary and functional differentiation of CRY proteins between the two species. We report differences in subcellular localisation of each D. magna CRY protein when expressed in the Drosophila clock neuron. Circadian rhythm behavioural experiments revealed that D. magna CRYs are not functionally conserved in the Drosophila molecular clock. These findings provide a new perspective on the evolutionary conservation of CRY, as functions of the four D. magna CRY proteins have diverse subcellular localisation levels. Furthermore, molecular clocks of D. magna have been evolutionarily differentiated from those of Drosophila. This study highlights the extensive functional diversity existing among species in their complement of Cry genes.

The power of numbers: dynamics of hatching and dormant egg production in two populations of the water flea Daphnia magna

Many organisms that live in inland standing waters produce dormant life stages that can accumulate in propagule banks to survive temporarily unfavourable periods. These egg banks have important effects on the ecology of populations and communities in terms of phenology, population densities, the probability of extinction, species diversity and habitat connectivity in time and space. They also have important consequences for the evolutionary versatility of populations. Although diapause and dormant egg banks in freshwater zooplankton have been studied for several decades, little is known about the quantitative contribution of egg production and hatching to yearly egg bank budgets and their seasonality in natural ponds and lakes. Here we quantified inter- and intra-annual variation in hatching and dormant egg production in the water flea Daphnia magna in two natural shallow ponds in Flanders (Belgium) using high-intensity sampling and in situ measurements. Hatching started in spring and occurred in several bouts (April–July), accumulating to a yearly average total of 3.5 × 103 hatchlings m−2. Dormant egg production occurred in one-to-three bouts mainly during late spring and summer (May–August), resulting in a total yearly production ranging from 1.2 × 104 up to 17.3 × 104 ephippia m−2. In both years, there was an average surplus of 3.14 × 104 and 15.24 × 104 ephippia produced m−2 for ponds OM2 and OM3, respectively, contributing to the accumulation of the persistent egg bank. We discuss the ecological and evolutionary consequences of both the high number of ephippia that are produced and the high number of hatchlings at the start of each growing season.

Influence of nanoplastic surface charge on eco-corona formation, aggregation and toxicity to freshwater zooplankton

Concerns about possible environmental implications of nano- and micro-plastics are continuously raising. Hence, comprehensive understanding of their behaviour, bioaccumulation and toxicity potential is required. Nevertheless, systematic studies on their fate and possible effects in freshwaters, as well as the influence of particle-specific and environmental factors on their behaviour and impacts are still missing. The aims of the present study are thus two-fold: (i) to examine the role of the surface charge on nanoplastic stability and acute effects to freshwater zooplankton; (ii) to decipher the influence of the refractory natural organic matter (NOM) on the nanoplastic fate and effects. Amidine and carboxyl-stabilized polystyrene (PS) spheres of 200 nm diameter characterized by opposite primary surface charges and neutral buoyancy were selected as model nanoplastics. The results demonstrated that the surface functionalization of the polystyrene nanoplastics controls their aggregation behaviour. Alginate or Suwannee River humic acid (SRHA) modified significantly the surface charge of positively-charged amidine PS nanoplastic and the aggregation state, while had no significant influence on the negatively-charged carboxyl PS nanoplastic. Both amidine and carboxyl PS nanoplastics were ingested by the zooplankton and concentrated mainly in the gut of water flea Daphnia magna and larvae Thamnocephalus platyurus, and the stomach of rotifer Brachionus calyciflorus. Amidine PS nanoplastic was more toxic than carboxyl one. The toxicity decreased in the order D. magna (48 h -immobilization) > B. calyciflorus (24 h - lethality) > T. platyurus (24 h - lethality). Alginate or SRHA reduced significantly the toxicity of both amidine and carboxyl PS nanoplastics to the studied zooplankton representatives. The implications of this laboratory study findings to natural environment were discussed.

Toxicity of tailing leachates from a niobium mine toward three aquatic organisms

The aim of this research was to assess the ecotoxicity of leachates originating from a niobium mine located in Canada. These tailings contain considerable amounts of carbonates and phosphates and could potentially be used as fertilizer for agriculture. However, the presence of different contaminants linked with the ores mined, including rare earth elements and daughter elements of the uranium disintegration chain is of concern. Bioassays have been used to determine if the tailings leachates could be harmful. The assessment of the toxicity of progressive dilutions of five tailing leachates (808, 809, 810, 811 and 897) was performed on different organisms: phytoplankton Raphidocelis subcapitata and duckweed Lemna minor, based on their growth and chlorophyll a content, and water flea Daphnia magna based on their mobility, mortality and reproduction. Overall, the leachates showed higher toxicity to Raphidocelis subcapitata and Lemna minor, than toward Daphnia magna. Leachate 808 showed no toxicity to all organisms while leachate 810 showed significant effects to all species. The results can be explained by the leachate dissolved metal or nutrient concentrations, but also by the metal bioavailability which depends on pH and hardness. Generally, toxicity was observed in undiluted samples tested, which is not representative of the conditions that could occur in the environment. This supports the idea that these tailings could be used as fertilizer albeit more studies may be required, particularly to assess the toxicity of the tailings leachate for benthic organisms, the toxicity of the tailings for terrestrial organisms and the variations of soil and sediment physicochemical properties after tailing treatments.

Shedding light on the effects of hydraulic fracturing flowback and produced water on phototactic behavior in Daphnia magna

The effluent produced during hydraulic fracturing (i.e. flowback and produced water; FPW), is a complex hyper-saline solution that is known to negatively impact the survival and the fitness of the water flea Daphnia magna, but to date effects on behavior are unstudied. In the current study, the effects of FPW on phototactic behavior of D. magna were examined. Exposure of naïve animals to FPW resulted in a dose-dependent increase in the speed of appearance of daphnids in the illuminated zone of the test apparatus (i.e. a faster positive phototaxis response). A similar dose-dependent response was observed in a test solution where the salt content of FPW was recreated in the absence of other components, suggesting that the effect was largely driven by salinity. The effect of FPW was significant when the raw FPW sample was diluted to 20% of its initial strength, while the effect of salt-matched solution was significant at a 10% dilution. A distinct effect was observed following FPW pre-exposure. After a 24 h pre-exposure to 1.5% FPW, Daphnia displayed a significantly inhibited positive phototaxis response when examined in control water, relative to control animals that were not pre-exposed to FPW. This effect was not observed in salinity pre-exposed animals, however these daphnids displayed a significantly reduced phototactic response when tested in saline waters, indicating a loss of the positive phototaxis seen in naïve organisms. These data indicate that FPW can induce perturbations in the behavior of aquatic invertebrates, an effect that may influence processes such as feeding and predation rates.

Study of Influence of Drilling Wastes on Black Sea Planktonic and Benthic Organisms

The aim of this study was to evaluate the impact of modeled drilling wastes on planktonic and benthic organisms of the Tuapse trough of the Black Sea. The extension of shelf turbidity area due to drilling is calculated using VOSTOK software package for water-oil- and water-based drilling muds (WODM and WDM). The maximum impact on the diatom (Phaedactylum tricornutum) population was achieved after 96 h of incubation at 20 mg/liter drilling wastes concentration. Acute lethal effect on water fleas (Daphnia magna) was observed only at high concentrations of suspension of drilling wastes (above 1 g/liter) in the seawater. In real conditions, such a concentration is attained only in the immediate proximity of the waste disposal site. Delayed effects, namely, fertility decline and maturation and growth delay, which resulted from short-term impact in the area of increased turbidity, were established. Mollusks (mussels) exhibited resistance to the impact of drilling wastes, but a marked deterioration occurred in their physiological state.

The genome of the freshwater water flea Daphnia magna: A potential use for freshwater molecular ecotoxicology

The water flea Daphnia magna is a small planktonic cladoceran. D. magna has been used as a model species for ecotoxicology, as it is sensitive to environmental stressors and environmental changes. Since Daphnia is affected by culture environment and each population/strain has its own ecological and genetic characteristics, its population/strain-based genome information is useful for environmental genomic studies. In this study, we assembled and characterized the genome of D. magna. Using a high-density genetic map of D. magna xinb3, the draft genome was integrated to 10 linkage groups (LGs). The total length of the integrated genome was about 123 Mb with N50 = 10.1 Mb, and the number of scaffolds was 4193 including 10 LGs. A total of 15,721 genes were annotated after manual curation. Orthologous genes were characterized in the genome and compared with other genomes of Daphnia. In addition, we identified defense related genes such as cytochrome P450 (CYP) genes, glutathione S-transferase (GST) genes, and ATP-binding cassette (ABC) genes from the assembled D. magna genome for its potential use in molecular ecotoxicological studies in the freshwater environment. This genomic resource will be helpful to study for a better understanding on molecular mechanism in response to various pollutants.

Observations of water-flea Daphnia magna and avian fecalia in rock pools: is traditional natural history reporting still relevant for science?

ABSTRACTUnexpected observation of freshwater invertebrate Daphnia magna in temporary rock pools on a small island off the Norwegian Atlantic coast confirms colonising ability, mediated through avian dispersal. Robust diapausal eggs of D. magna pass the gut of migrating geese and subsequently hatch in environments where such waterfowl forage and rest along migrating routes. The incubation experiment demonstrates that decomposing fecalia of geese constitute sufficient feed to support developing populations of D. magna in experimental oligotrophic conditions. The findings also show that D. magna is highly adapted for colonisation of temporary pools north of the Arctic Polar Circle, with excellent tolerance to low temperatures. Discussion part I relates the findings to published evidence on avian transport of invertebrate propagules, such as correlations between migration patterns of waterfowl and geographical patterns of aquatic invertebrate diversity. Discussion part II reflects on academic cultures, epistemological aspects of natural history reporting, the presence of a whale cadaver as an ecological indicator and the relevance of simple observation as a starting point for further discourse.