•The total length of the D. magna genome was about 123 Mb with N50 = 10.1 Mb.•The number of scaffolds was 4,193 including 10 LGs.•A total of 15,721 genes were annotated after manual curation.•Defense ...related genes such as 43 CYP, 22 GST, and 62 ABC genes were identified.
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.
Sewer overflows are an environmental concern due to their potential to introduce contaminants that can adversely affect downstream aquatic ecosystems. As these overflows can occur during rainfall ...events, the influence of rainwater ingress from inflow and infiltration on raw untreated wastewater (influent) within the sewer is a critical factor influencing the dilution and toxicity of the contaminants. The Vineyard sewer carrier in the greater city of Sydney, Australia, was selected for an ecotoxicological investigation of a sanitary (separate to stormwater) sewerage system and a wet-weather overflow (WWO). Three influent samples were collected representing dry-weather (DW), intermediate wet-weather (IWW) and wet-weather (WW). In addition, a receiving water sample was also collected downstream in Vineyard Creek (WW-DS) coinciding with a WWO.
We employed direct toxicity assessment (DTA) and toxicity identification evaluation (TIE) approaches to gain comprehensive insights into the nature and magnitude of the impact on influent from rainwater ingress into the sewer. Three standard ecotoxicological model species, a microalga, Chlorella vulgaris, the water flea, Ceriodaphnia dubia and the midge larva, Chironomus tepperi were used for both acute and chronic tests. The study revealed variable toxicity responses, with the sample of influent collected in wet-weather displaying lower toxicity compared to the dry-weather sample of influent. Ammonia, and metals, were identified in dry weather as contributors to the observed toxicity, however, this risk was alleviated through rainwater ingress in wet-weather with further dilution within the receiving water. Based on toxicity data, dilutions of influent to minimise effects on C. vulgaris and C. dubia ranged from 1 in 12 in DW to 1 in 2.8 in WW, and further diminished in the receiving water to 1 in 1.8. The successful application of ecotoxicological approaches enabled the assessment of cumulative effects of contaminants in influent, offering valuable insights into sanitary sewer system under rainwater ingress.
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•Toxicity varied between rainfall infiltration events and test species.•Dry-weather sanitary-sewer influent exhibited greatest toxicity that reduced with dilution.•Non-toxic acute testing results from wet-weather influent and downstream samples.•Required chronic test dilutions of 1 in 12 in dry-weather to 1 in 1.8 under wet-weather•Ammonia along with copper and zinc were identified contributors to toxicity under TIE.
Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are two types of perfluorinated compounds (PFCs) frequently studied in recent years due to their potential for bioaccumulation and ...toxicity to humans. Usually, PFCs can co-exist in various environment. Therefore, over- or under-estimated risk assessments would result if antagonism or synergism occurred in mixture toxicity. In the present study, the acute and chronic toxicities of single and mixtures of PFOA and PFOS to Daphnia magna were investigated. PFOS was more toxic than PFOA, both in 48-h acute toxicity and 21-d chronic toxicity. In acute toxicity tests, mixture toxicities showed strong synergistic effects on mortality. The experimental EC50 of the mixture is 4.44 × 10−5 mol/L, whereas the predicted EC50 is 8.19 × 10−5 mol/L by Concentration Addition Model and 9.73 × 10−5 mol/L by Independent Action Model. In chronic toxicity tests, synergistic effects were also found in the aspects of offspring. The offspring rate is reduced significantly to 39.8% at the 9.61 × 10−7 mol/L of mixture, while, PFOS and PFOA do not have effects when they are tested individually at corresponding concentrations. To explore the potential mechanism of the synergistic effect, the interactions between PFCs and proteins, including acetylcholinesterase, superoxide dismutase, catalase, ecdysone receptor and glutathione-S-transferase, were investigated by the Molecular Docking. The docking results revealed that the driving forces for the binding of PFCs with proteins were predominantly hydrophobic and hydrogen-bonding interactions. Based on the binding models, we deduced that the potential mechanism of synergism is that PFOS and PFOA have similar binding modes with catalase and have different binding modes with superoxide dismutase. Overall, these data provide experimental evidence that there is strong synergism in acute and chronic toxicity of mixtures to D. magna and demonstrate that molecular structure of some components of the antioxidant defence system contributes to the synergistic interaction.
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•The toxicity of PFOS is significantly higher than that of PFOA to D. magna.•The mixtures of PFOS and PFOA have strong synergism in acute and chronic toxicity.•PFOS and PFOA bind differently with SOD while bind similarly with CAT.
Since a mixed state of environmental contaminants, including microplastics (MPs), heavy metals, pharmaceuticals, and personal care products (PPCPs), exists in aquatic ecosystems, it is necessary to ...evaluate not only the adverse effects of exposure to a single stressor but to combined stressors. In this study, we exposed the freshwater water flea Daphnia magna to 2 μm MPs and triclosan (TCS), one of PPCPs, for 48 h to investigate the synergistic toxic consequences of simultaneous exposure to both pollutants. We measured in vivo endpoints, antioxidant responses, multixenobiotic resistance (MXR) activity, and autophagy-related protein expression via the PI3K/Akt/mTOR and MAPK signaling pathways. While MPs single exposure did not show toxic effects in water fleas, simultaneous exposure to TCS and MPs was associated with significantly greater deleterious effects in the form of increased mortality and alterations in antioxidant enzymatic activities compared with water fleas exposed to TCS alone. In addition, MXR inhibition was confirmed by measurement of the expression of P-glycoproteins and multidrug-resistance proteins in MPs-exposed groups, which led to the accumulation of TCS. Overall, these results suggest that simultaneous exposure to MPs and TCS resulted in higher TCS accumulation via MXR inhibition, leading to synergistic toxic effects such as autophagy in D. magna.
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•The simultaneous exposures to MPs and TCS were observed to have enhanced deleterious effects compared to TCS single exposure.•MP single exposure caused no significant toxic effects on water fleas.•P-glycoprotein and multidrug-resistance proteins following MPs exposure confirmed MXR inhibition.•The simultaneous MPs and TCS-exposed groups showed increased TCS toxicity and autophagy induction.
Little information is available about effect of particle size and crystal structure of nTiO2 on their trophic transfer. In this study, 5 nm anatase, 10 nm anatase, 100 nm anatase, 20 nm P25 (80% ...anatase and 20% rutile), and 25 nm rutile nTiO2 were selected to investigate the effects of size and crystal structure on the toxicity, bioconcentration, and trophic transfer of nTiO2 to algae and daphnia. In the exposed daphnids, metabolic pathways affected by nTiO2 and nTiO2-exposed algae (nTiO2-algae) were also explored. The 96 h IC50 values of algae and the 48 h LC50 values of daphnia were 10.3, 18.9, 43.9, 33.6, 65.4 mg/L and 10.5, 13.2, 37.0, 28.4, 60.7 mg/L, respectively, after exposed to nTiO2-5A, nTiO2-10A, nTiO2-100A, nTiO2-P25, and nTiO2-25R, respectively. The bioconcentration factors (BCFs) for 0.1, 1, and 10 mg/L nTiO2 in daphnia ranged from 21,220 L/kg to 145,350 L/kg. The nTiO2 biomagnification factors (BMFs) of daphnia fed with 1 and 10 mg/L nTiO2-exposed algae were consistently greater than 1.0 (5.7–122). The results show that the acute toxicity, BCF, and BMF all decreased with increasing size or rutile content of nTiO2. All types of nTiO2 were largely accumulated in the daphnia gut and were not completely depurated within 24 h. At the molecular level, 22 Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways of daphnia were impacted by the nTiO2 and nTiO2-algae treatments, including glutathione metabolism, aminoacyl-tRNA biosynthesis, among others. Six and four KEGG metabolic pathways were significantly disturbed in daphnids exposed to nTiO2 and nTiO2-algae, respectively, indicating the presence of algae partially alleviated the negative impact of nTiO2 on metabolism. These findings increase understanding of the impacts of physicochemical properties of nTiO2 on the food chain from molecular scale to that of the whole organism, and provide new insight into the ecological effect of nanomaterials.
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•Effects of five nTiO2 types on daphnia with or without algae were studied.•Bioconcentration and biomagnification were all observed for the five nTiO2.•The toxicity, bioconcentration, and biomagnification decreased with increasing size or rutile content of nTiO2.•Anatase nTiO2 affected the metabolism of daphnia differently from rutile ones.
The toxicity, bioconcentration, and biomagnification of nTiO2 decreased with increasing size or rutile content.
•ResNet_152 was the best evaluation network for DeepLabCut in Daphnia pose tracking.•The novel method is complemented with VBA to reduce manual work and human errors.•This method showed comparable ...results with the previous methods.•The accuracy of this method was verified by evaluating IMI and PEN cardiotoxicity.
Daphnia magna is one species of water flea that has been used for a long time for ecotoxicity studies. In addition, Daphnia has a myogenic heart that is very useful for cardiotoxicity studies. Previous attempts to calculate the cardiac parameter endpoints in Daphnia suffer from the drawback of tedious operation and high variation due to manual counting errors. Even the previous method that utilized deep learning to help the process suffer from either overestimation of parameters or the need for specialized equipment to perform the analysis. In this study, we utilized DeepLabCut software previously used for animal pose tracking and demonstrated that ResNet_152 was the best fit for training the network. The trained network also showed comparable results with ImageJ and Kymograph, which was mostly done manually. In addition to that, several macro scripts in either Excel or Python format were developed to help summarize the data for faster analysis. The trained network was then challenged to analyze the potential cardiotoxicity of imidacloprid and pendimethalin in D. magna, and it showed that both pesticides cause alteration in their cardiac performance. Overall, this method provides a simple and automatic method to analyze the cardiac performance of Daphnia by utilizing DeepLabCut. The method proposed in this paper can contribute greatly to scientists conducting fast and accurate cardiotoxicity measurements when using Daphnia as a model.
Aqueous calcium (Ca) decline is threatening freshwater ecosystems worldwide. There are great concerns about the possible ecological consequences of Ca limitation combined with biological pressures ...like predation. Here we investigated the interactions between Ca restriction and fish predation risk on the phenotypic plasticity in the keystone herbivore Daphnia, together with physiological responses underlying the plastic trait changes. Fish predation risk induced D. pulex to mature earlier and produce more but smaller offspring at adequate Ca. Declining Ca inhibited the expression of defensive traits, with the inhibitive degree showing a linear or threshold-limited dynamic. The presence of predation risk mitigated the negative effect of declining Ca on reducing body size but exacerbated the delay in maturity, indicating a life history trade-off for larger body size rather than the current reproduction in multi-stressed Daphnia. Actin 3-mediated cytoskeleton and AMPK β-mediated energy metabolism were highly correlated with these plastic trait changes. Altered phenotypic plasticity in planktonic animals is expected to trigger many ecological impacts from individual fitness to community structure, thus providing new insights into the mechanisms underlying decreased Ca affecting lake ecosystems.
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•Declining Ca inhibits predation-induced trait expression in Daphnia.•Predation mitigates the reducing effect of declining Ca on body size.•Predation exacerbates the delay in maturity caused by declining Ca.•Daphnia showed life history trade-offs for larger body size rather than reproduction.•Trait responses are correlated with changes in cytoskeleton and energy metabolism.
Adverse effects of microplastics (MPs) are exacerbated by plastic additives such as benzophenone-3 (BP-3). The aim of the present study was to evaluate the role of extracellular polymeric substances ...(EPS) of Chlorella vulgaris in leaching BP-3 additive (3.0 ± 0.2% wt/wt) from polyethylene MP fragments (99.8 ± 4.1 µm) and subsequent bioconcentration in Daphnia magna. BP-3 leaching in M4 medium was higher at pH 8 than at pH 6, because of the higher solubility of BP-3 (pKa=7.07) at pH 8. However, EPS reduced BP-3 leaching in M4 medium, possibly because of repulsive interactions between the negatively charged EPS and anionic BP-3. Thus, BP-3 leaching was greater at lower pH (6 >8) and EPS concentration (20 >50 mg L−1 as total organic carbon), which was well related to BP-3 sorption capacity of EPS. Although BP-3 uptake in D. magna was decreased at pH 8 by increasing EPS concentration, the bioconcentration of BP-3 in D. magna was increased, possibly because of reduced BP-3 elimination. These findings suggest the important role of EPS in the bioconcentration of anionic plastic additives, which should be further evaluated to understand the underlying toxicokinetic mechanisms.
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•Benzophenone‐3 (BP-3) leaching from microplastic (MP) fragments depends on pH.•Extracellular polymeric substances (EPS) reduce BP-3 leaching at pH 6 and 8.•EPS increase BP‐3 bioconcentration in Daphnia magna clearly at pH 8.
Multigenerational toxicity testing is a valuable tool for understanding the long-term effects of contaminants on aquatic organisms. This review focuses on the use of multigenerational tests with ...Daphnia, a widely used model organism in aquatic toxicological studies. The review highlights the importance of studying multiple generations to assess Daphnia spp. reproductive, growth, and physiological responses to various contaminants.
We discuss the outcomes of multigenerational tests involving different contaminants, including nanoparticles, pesticides, and pharmaceuticals. The results reveal that multigenerational exposure can lead to transgenerational effects, where the impacts of contaminants are observed in subsequent generations even after the initial exposure has ceased. These transgenerational effects often manifest as reproduction, growth, and development alterations.
Furthermore, we emphasize the need for standardized protocols in multigenerational testing to ensure comparability and reproducibility of results across studies. We also discuss the implications of multigenerational testing for ecological risk assessment, as it provides a more realistic representation of the long-term effects of contaminants on populations and ecosystems.
Overall, this review highlights the significance of multigenerational tests with Daphnia in advancing our understanding of the ecological impacts of contaminants. Such tests provide valuable insights into the potential risks associated with long-term exposure to pollutants and contribute to the development of effective mitigation strategies for aquatic ecosystems.
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•Environmental contaminants' effects on Daphnia magna are examined, revealing potential risks.•Multigenerational assays are assessed, covering protocols, advantages, and limitations.•Multigenerational assays depict long-term impacts of contaminants by spanning generations
Heavy metals such as lead (Pb), cadmium (Cd), and arsenic (As) are of great concern in aquatic ecosystems because of their global distribution, persistence, and biomagnification via the food web. ...They can induce the expression of cellular protective systems (e.g., detoxification enzymes and antioxidant enzymes) to protect organisms from oxidative stress, which is a high-energy-consuming process. Thus, energy reserves (e.g., glycogen, lipids, and proteins) are utilized to maintain metabolic homeostasis. Although a few studies have suggested that heavy metal stress can modulate the metabolic cycle in crustaceans, information on changes in energy metabolism under metal pollution remains lacking in planktonic crustaceans. In the present study, the activity of digestive enzymes (amylase, trypsin, and lipase) and the contents of energy storage molecules (glycogen, lipid, and protein) were examined in the brackish water flea Diaphanosoma celebensis exposed to Cd, Pb, and As for 48 h. Transcriptional modulation of the three AMP-activated protein kinase (AMPK) and metabolic pathway-related genes was further investigated. Amylase activity was highly increased in all heavy metal-exposed groups, whereas trypsin activity was reduced in Cd- and As-exposed groups. While glycogen content was increased in all exposed groups in a concentration-dependent manner, lipid content was reduced at higher concentrations of heavy metals. The expression of AMPKs and metabolic pathway-related genes was distinct among heavy metals. In particular, Cd activated the transcription of AMPK-, glucose/lipid metabolism-, and protein synthesis-related genes. Our findings indicate that Cd can disrupt energy metabolism, and may be a potent metabolic toxicant in D. celebensis. This study provides insights into the molecular mode of action of heavy metal pollution on the energy metabolism in planktonic crustaceans.
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•Amylase activity increased in all heavy metal-exposed groups.•Trypsin activity decreased in the Cd- and As-exposed groups.•Glycogen and lipid contents were modulated at varying metal concentration.•Cd activates the transcription of metabolism-related genes.•Cd may be a potent metabolic toxicant in D. celebensis.
