Transcriptional responses in neonate and adult Daphnia magna in relation to relative susceptibility to genotoxicants

Adverse effects of the 5-alpha-reductase inhibitor finasteride on Daphnia magna: Endocrine system and lipid metabolism disruption

Finasteride, a steroid 5-alpha reductase inhibitor, is commonly used for the treatment of benign prostatic hyperplasia and hair loss. However, despite continued use, its environmental implications have not been thoroughly investigated. Thus, we investigated the acute and chronic adverse impacts of finasteride on Daphnia magna, a crucial planktonic crustacean in freshwater ecosystems selected as bioindicator organism for understanding the ecotoxicological effects. Chronic exposure (for 23 days) to finasteride negatively affected development and reproduction, leading to reduced fecundity, delayed first brood, reduced growth, and reduced neonate size. Additionally, acute exposure (< 24 h) caused decreased expression levels of genes crucial for reproduction and development, especially EcR-A/B (ecdysone receptors), Jhe (juvenile hormone esterase), and Vtg2 (vitellogenin), with oxidative stress-related genes. Untargeted lipidomics/metabolomic analyses revealed lipidomic alteration, including 19 upregulated and 4 downregulated enriched lipid ontology categories, and confirmed downregulation of metabolites. Pathway analysis implicated significant effects on metabolic pathways, including the pentose phosphate pathway, histidine metabolism, beta-alanine metabolism, as well as alanine, aspartate, and glutamate metabolism. This comprehensive study unravels the intricate molecular and metabolic responses of D. magna to finasteride exposure, underscoring the multifaceted impacts of this anti-androgenic compound on a keystone species of freshwater ecosystems. The findings emphasize the importance of understanding the environmental repercussions of widely used pharmaceuticals to protect biodiversity in aquatic ecosystems.

Transcriptomic Analysis of Diethylstilbestrol in Daphnia Magna: Energy Metabolism and Growth Inhibition

With the widespread use of diethylstilbestrol (DES), it has become a common contaminant in the aquatic environment. It is toxic to a wide range of aquatic organisms, disrupting the water flea growth and further interfering with several ecosystem services. Nevertheless, the molecular mechanism of DES in water fleas is still unexplicit. In this study, the 21-day chronic test showed that a negative effect of growth and reproduction can be observed with DES exposure. Subsequently applied transcriptomic analysis illustrated the molecular mechanism in mode freshwater invertebrate Daphnia magna (D. magna) exposed to 2, 200, and 1000 μg·L^-1 of DES for 9 days. Meanwhile, exposure to DES at 200 and 1000 μg·L^-1 significantly restrains the growth (body length) and reproduction (first spawning time) of D. magna. Identified differentially expressed genes (DEGs) are majorly enriched relative to energy metabolism, lipid metabolism, the digestive system, transport and catabolism pathways which were remarkably changed. These repressed and up-regulated pathways, in relation to energy synthesis and metabolism, may be the reasons for the reduced body length and delayed first spawning time. Taken together, this study revealed that DES is a threat to D. magna in the aquatic environment and clarifies the molecular mechanism of the toxicity.

Effects of glyphosate on cladocera: A synthetic review

Glyphosate [N-(phosphonomethyl) glycine] is currently the most widely used herbicide worldwide. Its application in agricultural and urban areas can lead to the dispersion and arrival to aquatic systems causing environmental deterioration with detrimental effects on the inhabiting biota. This is triggered not only by the herbicide per se but also its metabolite aminomethyl-phosphonic acid (AMPA), which can be highly toxic to many aquatic organisms. Water fleas are some of the key components in aquatic food webs, being one of the most sensitive groups to pollutants. Although being often used in standardized toxicity tests, they are comparatively less studied in relation to glyphosate exposition. Here we examine the current scientific literature regarding the acute and sublethal toxicity of glyphosate in the Cladocera taxonomic group, with special comparisons between the active ingredient (A.I) and formulations. Our results document a high variation in the lethal concentrations reported for different cladoceran species, due to the high diversity of products used in the toxicity tests. Most articles accounting for sublethal effects were performed on the standard Daphnia magna species. Reproduction, including decreased fecundity and delayed age of first reproduction, is usually one of the most severely affected individual traits. Although still scarce, studies documenting metabolic and genetic alterations might provide accurate information on the mechanisms of action of the herbicide.

Effects of water produced by oil segment on aquatic organisms after treatment using advanced oxidative processes

The water produced (PW) by the petroleum industry is a potential contaminant to aquatic biota, due to its complex mixture that may contain polycyclic aromatic hydrocarbons (PAHs), organic chemical compounds, including benzene, toluene, ethylbenzene and xylene (BTEX), metals and other components that are known to be toxic. The aim of this investigation was to examine the acute toxicity produced by a PW sample in aquatic organisms Vibrio fischeri and Daphnia similis prior to and after 4 treatments using advanced oxidative processes such as photocatalysis, photoelectrocatalysis, ozonation and photoelectrocatalytic ozonation. Data demonstrated that exposure to PW was toxic to both organisms, as evidenced by reduced luminescence in bacterium Vibrio fischeri and induced immobility in Daphnia similis. After treatment of PW with 4 different techniques, the PW remained toxic for both tested organisms. However, photoelectrocatalysis was more efficient in decreasing toxicity attributed to PW sample. Therefore, data demonstrate the importance of treating PW for later disposal in the environment in order to mitigate ecotoxicological impacts. Further photoelectrocatalysis appeared to be a promising tool for treating PW samples prior to disposal and exposure of aquatic ecosystems.

Cell free Microcystis aeruginosa spent medium affects Daphnia magna survival and stress response

Primary consumers in freshwater ecosystems, such as the zooplankton organism Daphnia magna, are highly affected by cyanobacteria, both as they may use it as a food source but also by cyanobacterial metabolites present in the water. Here, we investigate the impacts of cyanobacterial metabolites focussing on the environmental realistic scenario of the naturally released mixture without crushing cyanobacterial cells or their uptake as food. Therefore, D. magna were exposed to two concentrations of cell free cyanobacterial spent medium from Microcystis aeruginosa PCC 7806 to represent higher and lower ecologically-relevant concentrations of cyanobacterial metabolites. Including microcystin-LR, 11 metabolites have been detected of which 5 were quantified. Hypothesising concentration and time dependent negative impact, survival, gene expression marking digestion and metabolism, oxidative stress response, cell cycle and molting as well as activities of detoxification and antioxidant enzymes were followed for 7 days. D. magna suffered from oxidative stress as both catalase and glutathione S-transferase enzyme activities significantly decreased, suggesting enzyme exhaustibility after 3 and 7 days. Moreover, gene-expressions of the 4 stress markers (glutathione S-transferase, glutathione peroxidase, catalase and thioredoxin) were merely downregulated after 7 days of exposure. Energy allocation (expression of glyceraldehyde-3-phosphate dehydrogenase) was increased after 3 days but decreased as well after 7 days exposure. Cell cycle was impacted time dependently but differently by the two concentrations, along with an increasing downregulation of myosin heavy chain responsible for cell arrangement and muscular movements. Deregulation of nuclear hormone receptor genes indicate that D. magna hormonal steering including molting seemed impaired despite no detection of microviridin J in the extracts. As a consequence of all those responses and presumably of more than investigated molecular and physiological changes, D. magna survival was impaired over time, in a concentration dependent manner. Our results confirm that besides microcystin-LR, other secondary metabolites contribute to negative impact on D. magna survival and stress response.

RIBE at an inter-organismic level: A study on genotoxic effects in Daphnia magna exposed to waterborne uranium and a uranium mine effluent

The induction of RIBE (Radiation Induced Bystander Effect) is a non-target effect of low radiation doses that has already been verified at an inter-organismic level in fish and small mammals. Although the theoretical impact in the field of environmental risk assessment (ERA) is possible, there is a gap of knowledge regarding this phenomenon in invertebrate groups and following environmentally relevant exposures. To understand if RIBE should be considered for ERA of radionuclide-rich wastewaters, we exposed Daphnia magna (<24 h and 5d old) to a 2% diluted uranium mine effluent for 48 h, and to a matching dose of waterborne uranium (55.3 μg L^-1). Then the exposed organisms were placed (24 and 48 h) in a clean medium together with non-exposed neonates. The DNA damage observed for the non-exposed organisms was statistically significant after the 24 h cohabitation for both uranium (neonates p = 0.002; 5 d-old daphnids p = <0.001) and uranium mine effluent exposure (only for neonates p = 0.042). After 48 h cohabitation significant results were obtained only for uranium exposure (neonates p = 0.017; 5 d-old daphnids p = 0.013). Although there may be some variability associated to age and exposure duration, the significant DNA damage detected in non-exposed organisms clearly reveals the occurrence of RIBE in D. magna. The data obtained and here presented are a valuable contribution for the discussion about the relevance of RIBE for environmental risk assessment.

Mixture effects in samples of multiple contaminants - An inter-laboratory study with manifold bioassays

Chemicals in the environment occur in mixtures rather than as individual entities. Environmental quality monitoring thus faces the challenge to comprehensively assess a multitude of contaminants and potential adverse effects. Effect-based methods have been suggested as complements to chemical analytical characterisation of complex pollution patterns. The regularly observed discrepancy between chemical and biological assessments of adverse effects due to contaminants in the field may be either due to unidentified contaminants or result from interactions of compounds in mixtures. Here, we present an interlaboratory study where individual compounds and their mixtures were investigated by extensive concentration-effect analysis using 19 different bioassays. The assay panel consisted of 5 whole organism assays measuring apical effects and 14 cell- and organism-based bioassays with more specific effect observations. Twelve organic water pollutants of diverse structure and unique known modes of action were studied individually and as mixtures mirroring exposure scenarios in freshwaters. We compared the observed mixture effects against component-based mixture effect predictions derived from additivity expectations (assumption of non-interaction). Most of the assays detected the mixture response of the active components as predicted even against a background of other inactive contaminants. When none of the mixture components showed any activity by themselves then the mixture also was without effects. The mixture effects observed using apical endpoints fell in the middle of a prediction window defined by the additivity predictions for concentration addition and independent action, reflecting well the diversity of the anticipated modes of action. In one case, an unexpectedly reduced solubility of one of the mixture components led to mixture responses that fell short of the predictions of both additivity mixture models. The majority of the specific cell- and organism-based endpoints produced mixture responses in agreement with the additivity expectation of concentration addition. Exceptionally, expected (additive) mixture response did not occur due to masking effects such as general toxicity from other compounds. Generally, deviations from an additivity expectation could be explained due to experimental factors, specific limitations of the effect endpoint or masking side effects such as cytotoxicity in in vitro assays. The majority of bioassays were able to quantitatively detect the predicted non-interactive, additive combined effect of the specifically bioactive compounds against a background of complex mixture of other chemicals in the sample. This supports the use of a combination of chemical and bioanalytical monitoring tools for the identification of chemicals that drive a specific mixture effect. Furthermore, we demonstrated that a panel of bioassays can provide a diverse profile of effect responses to a complex contaminated sample. This could be extended towards representing mixture adverse outcome pathways. Our findings support the ongoing development of bioanalytical tools for (i) compiling comprehensive effect-based batteries for water quality assessment, (ii) designing tailored surveillance methods to safeguard specific water uses, and (iii) devising strategies for effect-based diagnosis of complex contamination.

Transcriptomic approach: A promising tool for rapid screening nanomaterial-mediated toxicity in the marine bivalve Mytilus edulis-Application to copper oxide nanoparticles

The extensive development of nanotechnologies will inevitably lead to the release of nanomaterials (NMs) in the environment. As the aquatic environments represent the ultimate sink for various contaminants, it is highly probable that they also constitute a reservoir for NMs and hence aquatic animals represent potential targets. In a regulatory perspective, it is necessary to develop tools to rapidly screen the impact of NMs on model organisms, given that the number of NMs on the market will be increasing. In this context High Throughput Screening approaches represent relevant tools for the investigation of NM-mediated toxicity. The objective of this work was to study the effects of copper oxide nanoparticles (CuONPs) in the marine bivalve Mytilus edulis, using a transcriptomic approach. Mussels were exposed in vivo to CuONPs (10 μg·L^-1CuO NPs) for 24 h and analysis of mRNA expression levels of genes implicated in immune response, antioxidant activities, cell metabolism, cell transport and cytoskeleton was investigated by qPCR on hemocytes and gills. Results showed common effects of CuONPs and its ionic counterpart. However, greater effects of CuONPs on GST, SOD, MT, Actin, ATP synthase gene expressions were observed compared to ionic form indicating that toxicity of CuONPs is not solely due to the release of Cu²⁺. Even though M. edulis genome is not fully characterized, this study provides additional knowledge on the signaling pathways implicated in CuONP-mediated toxicity and demonstrates the reliability of using a qPCR approach to go further in the cellular aspects implicated in response to NPs in marine bivalves.

Genotoxicity of metal based engineered nanoparticles in aquatic organisms: A review

Engineered nanoparticles (ENPs) are an emerging class of environmental contaminants, but are generally found in very low concentrations and are therefore likely to exert sub-lethal effects on aquatic organisms. In this review, we: (i) highlight key mechanisms of metal-based ENP-induced genotoxicity, (ii) identify key nanoparticle and environmental factors which influence the observed genotoxic effects, and (iii) highlight the challenges involved in interpreting reported data and provide recommendations on how these challenges might be addressed. We review the application of eight different genotoxicity assays, where the Comet Assay is generally preferred due to its capacity to detect low levels of DNA damage. Most ENPs have been shown to cause genotoxic responses; e.g., DNA or/and chromosomal fragmentation, or DNA strand breakage, but at unrealistic high concentrations. The genotoxicity of the ENPs was dependent on the inherent physico-chemical properties (e.g. size, coating, surface chemistry, e.tc.), and the presence of co-pollutants. To enhance the value of published genotoxicity data, the role of environmental processes; e.g., dissolution, aggregation and agglomeration, and adsorption of ENPs when released in aquatic systems, should be included, and assay protocols must be standardized. Such data could be used to model ENP genotoxicity processes in open environmental systems.

Sublethal and Reproductive Effects of Acute and Chronic Exposure to Flowback and Produced Water from Hydraulic Fracturing on the Water Flea Daphnia magna

Hydraulic fracturing is an industrial process allowing for the extraction of gas or oil. To fracture the rocks, a proprietary mix of chemicals is injected under high pressure, which later returns to the surface as flowback and produced water (FPW). FPW is a complex chemical mixture consisting of trace metals, organic compounds, and often, high levels of salts. FPW toxicity to the model freshwater crustacean Daphnia magna was characterized utilizing acute (48 h median lethal concentrations; LC₅₀) and chronic (21 day) exposures. A decrease in reproduction was observed, with a mean value of 18.5 neonates produced per replicate over a 21 day chronic exposure to 0.04% FPW, which was a significant decrease from the average of 64 neonates produced in the controls. The time to first brood was delayed in the highest FPW (0.04%) treatment. Neonates exhibited an LC₅₀ of 0.19% of full-strength FPW, making them more sensitive than adults, which displayed an LC₅₀ value of 0.75%. Quantitative PCR highlighted significant changes in expression of genes encoding xenobiotic metabolism (cyp4) and moulting (cut). This study is the first to characterize chronic FPW toxicity and will help with the development of environmental monitoring and risk assessment of FPW spills.

Transcriptomic, cellular and life-history responses of Daphnia magna chronically exposed to benzotriazoles: Endocrine-disrupting potential and molting effects

Benzotriazoles (BZTs) are ubiquitous aquatic contaminants used in a wide range of industrial and domestic applications from aircraft deicers to dishwasher tablets. Acute toxicity has been reported in aquatic organisms for some of the BZTs but their mode of action remains unknown. The objectives of this study were to evaluate the transcriptomic response of D. magna exposed to sublethal doses of 1H-benzotriazole (BTR), 5-methyl-1H-benzotriazole (5MeBTR) and 5-chloro-1H-benzotriazole (5ClBTR) using RNA-sequencing and quantitative real-time PCR. Cellular and life-history endpoints (survival, number of neonates, growth) were also investigated. Significant effects on the molting frequency were observed after 21-d exposure to 5MeBTR and 5ClBTR. No effects on molting frequency were observed for BTR but RNA-seq results indicated that this BZT induced the up-regulation of genes coding for cuticular proteins, which could have compensated the molting disruption. Molting in cladocerans is actively controlled by ecdysteroid hormones. Complementary short-term temporal analysis (4- and 8-d exposure) of the transcription of genes related to molting and hormone-mediated processes indicated that the three compounds had specific modes of action. BTR induced the transcription of genes involved in 20-hydroxyecdysone synthesis, which suggests pro-ecdysteroid properties. 5ClBTR exposure induced protein activity and transcriptional levels of chitinase enzymes, associated with an impact on ecdysteroid signaling pathways, which could explain the decrease in molt frequency. Finally, 5MeBTR seemed to increase molt frequency through epigenetic processes. Overall, results suggested that molting effects observed at the physiological level could be linked to endocrine regulation impacts of BZTs at the molecular level.

Prediction and assessment of ecogenotoxicity of antineoplastic drugs in binary mixtures

The combined genotoxic effects of four anticancer drugs (5-fluorouracil [5-FU], cisplatin [CDDP], etoposide [ET], and imatinib mesylate [IM]) were studied testing their binary mixtures in two crustaceans that are part of the freshwater food chain, namely Daphnia magna and Ceriodaphnia dubia. Genotoxicity was assessed using the in vivo comet assay. Assessment was based on two distinct effect sizes determined from dose-response experiments. Doses for single and combined exposures expected to result in these effect sizes were computed based on Bliss independence as reference model. Statistical comparison by analysis of variance of single and combined toxicities allowed accepting or rejecting the independency hypothesis. The results obtained for D. magna showed independent action for all mixtures except for IM+5-FU that showed an antagonistic interaction. In C. dubia, most mixtures had antagonist interactions except IM+5-FU and IM+CDDP that showed Bliss independence. Despite the antagonistic interactions, our results demonstrated that combinations of anticancer drugs could be of environmental concern because effects occur at very low concentrations that are in the range of concentrations encountered in aquatic systems.

DNA alterations and effects on growth and reproduction in Daphnia magna during chronic exposure to gamma radiation over three successive generations

This study examined chronic effects of external Cs-137 gamma radiation on Daphnia magna exposed over three successive generations (F0, F1 and F2) to environmentally relevant dose rates (ranging from 0.007 to 35.4 mGy h(-1)). Investigated endpoints included survival, growth, reproduction and DNA alterations quantified using random-amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). Results demonstrated that radiation effects on survival, growth and reproduction increased in severity from generation F0 to generation F2. Mortality after 21 days at 35.4 mGy h(-1) increased from 20% in F0 to 30% in F2. Growth was affected by a slight reduction in maximum length at 35.4 mGy h(-1) in F0 and by reductions of 5 and 13% in growth rate, respectively, at 4.70 and 35.4 mGy h(-1) in F2. Reproduction was affected by a reduction of 19% in 21 day-fecundity at 35.4 mGy h(-1) in F0 and by a delay of 1.9 days in brood release as low as 0.070 mGy h(-1) in F2. In parallel, DNA alterations became significant at decreasing dose rates over the course of F0 (from 4.70 mGy h(-1) at hatching to 0.007 mGy h(-1) after ∼21 days) and from F0 to F2 (0.070 mGy h(-1) at hatching to 0.007 mGy h(-1) after ∼21 days), demonstrating their rapid accumulation in F0 daphnids and their transmission to offspring generations. Transiently more efficient DNA repair leading to some recovery at the organism level was suggested in F1, with no effect on survival, a slight reduction of 12% in 21 day-fecundity at 35.4 mGy h(-1) and DNA alterations significant at highest dose rates only. The study improved our understanding of long term responses to low doses of radiation at the molecular and organismic levels in a non-human species for a better radioprotection of aquatic ecosystems.

Eco-genotoxicity of six anticancer drugs using comet assay in daphnids

The eco-genotoxicity of six anti-neoplastic drugs, 5-fluorouracil, capecitabine, cisplatin, doxorubicin, etoposide, and imatinib, belonging to five classes of anatomical therapeutic classification (ATC), was studied applying the in vivo comet assay on cells from whole organisms of Daphnia magna and Ceriodaphnia dubia. For the first time, this test was performed in C. dubia. In addition, to have a wider genotoxic/mutagenic profile of the anticancer drugs selected, SOS chromotest and Salmonella mutagenicity assay were performed. The comet results showed that all drugs induced DNA damage, in both Cladocerans, with environmental concern; indeed Doxorubicin induced DNA damage in the order of tens of ng L(-1) in both crustaceans, as well as 5-flurouracil in C. dubia and cisplatin in D. magna. In the SOS Chromotest all drugs, except imatinib, were able to activate the repair system in Escherichia coli PQ37 while in the Salmonella mutagenicity assay, doxorubicin was the only drug able to cause direct and indirect frameshift and base-pair substitution mutations. Comet assay was the most sensitive tool of genotoxic exposure assessment, able to detect in vivo the adverse effects at concentration lower than those evaluated in vitro by bacterial assays.

Transcriptional changes during Daphnia pulex development indicate that the maturation decision resembles a rate more than a threshold

Maturation is a critical developmental process, and the age and size at which it occurs have important fitness consequences. Although maturation is remarkably variable, certain mechanisms, including a minimum size or state threshold, are proposed to underlie the process across a broad diversity of taxa. Recent evidence suggests that thresholds may themselves be developmentally plastic, and in the crustacean Daphnia pulex it is unclear whether maturation follows a threshold or is a gradual process more akin to a rate. Changes in gene expression across four instars before and during maturation were compared in a cDNA microarray experiment. Developmental stage was treated statistically both as a discontinuous and as a continuous variable, to determine whether genes showed gradual or discrete changes in expression. The continuous analysis identified a greater number of genes with significant differential expression (45) than the discontinuous analysis (11). The majority of genes, including those coding for histones, factors relating to transcription and cell cycle processes, and a putative developmental hormone showed continuous increases or decreases in expression from the first to the fourth instars that were studied, suggestive of a prolonged and gradual maturation process. Three genes coding for a fused vitellogenin/superoxide dismutase showed increases in expression following the second instar and coincided with the posited maturation threshold, but even their expression increased in a continuous fashion.

Comet Assay on Daphnia magna in eco-genotoxicity testing

Detection of potentially hazardous compounds in water bodies is a priority in environmental risk assessment. For the evaluation and monitoring of water quality, a series of methodologies may be applied. Among them, the worldwide used toxicity tests with organisms of the genus Daphnia is one of the most powerful. In recent years, some attempts were made to utilize Daphnia magna in genotoxicity testing as many of the new environmental contaminants are described as DNA-damaging agents in aquatic organisms. The aim of this research was to develop a highly standardized protocol of the Comet Assay adapted for D. magna, especially regarding the isolation of cells derived from the same tissue (haemolymph) from newborn organisms exposed in vivo. Several methods for haemolymph extraction and different Comet Assay parameters were compared. Electrophoretic conditions were adapted in order to obtain minimum DNA migration in cells derived from untreated organisms and, at the same time, maximum sensitivity in specimens treated with known genotoxicants (CdCl2 and H2O2). Additional tests were performed to investigate if life-history traits of the cladoceran (such as the age of adult organisms that provide newborns, the clutch size of origin, the number of generations reared in standard conditions) and the water composition as well, might influence the response of the assay. This study confirms the potential application of the Comet Assay in D. magna for assessing genotoxic loads in aqueous solution. The newly developed protocol could integrate the acute toxicity bioassay, thus expanding the possibility of using this model species in freshwater monitoring (waters, sediment and soil elutriates) and is in line with the spirit of the EU Water Framework Directive in reducing the number of bioassays that involve medium-sized species.

Genome-wide transcription profiles reveal genotype-dependent responses of biological pathways and gene-families in Daphnia exposed to single and mixed stressors

The present study investigated the possibilities and limitations of implementing a genome-wide transcription-based approach that takes into account genetic and environmental variation to better understand the response of natural populations to stressors. When exposing two different Daphnia pulex genotypes (a cadmium-sensitive and a cadmium-tolerant one) to cadmium, the toxic cyanobacteria Microcystis aeruginosa, and their mixture, we found that observations at the transcriptomic level do not always explain observations at a higher level (growth, reproduction). For example, although cadmium elicited an adverse effect at the organismal level, almost no genes were differentially expressed after cadmium exposure. In addition, we identified oxidative stress and polyunsaturated fatty acid metabolism-related pathways, as well as trypsin and neurexin IV gene-families as candidates for the underlying causes of genotypic differences in tolerance to Microcystis. Furthermore, the whole-genome transcriptomic data of a stressor mixture allowed a better understanding of mixture responses by evaluating interactions between two stressors at the gene-expression level against the independent action baseline model. This approach has indicated that ubiquinone pathway and the MAPK serine-threonine protein kinase and collagens gene-families were enriched with genes showing an interactive effect in expression response to exposure to the mixture of the stressors, while transcription and translation-related pathways and gene-families were mostly related with genotypic differences in interactive responses to this mixture. Collectively, our results indicate that the methods we employed may improve further characterization of the possibilities and limitations of transcriptomics approaches in the adverse outcome pathway framework and in predictions of multistressor effects on natural populations.

Transmission of DNA damage and increasing reprotoxic effects over two generations of Daphnia magna exposed to uranium

This study aimed to examine the mechanisms involved in the transgenerational increase in Daphnia magna sensitivity to waterborne depleted uranium (DU) under controlled laboratory conditions. Daphnids were exposed to concentrations ranging from 2 to 50 μg L(-1) over two successive generations. Genotoxic effects were assessed using random amplified polymorphic DNA and real time PCR (RAPD-PCR). Effects on life history (survival, fecundity and somatic growth) were monitored from hatching to release of brood 5. Different exposure regimes were tested to investigate the specific sensitivity of various life stages to DU. When daphnids were exposed continuously or from hatching to deposition of brood 5, results demonstrated that DNA damage accumulated in females and were transmitted to offspring in parallel with an increase in severity of effects on life history across generations. When daphnids were exposed during the embryo stage only, DU exposure induced transient DNA damage which was repaired after neonates were returned to a clean medium. Effects on life history remained visible after hatching and did not significantly increase in severity across generations. The present results suggest that DNA damage might be an early indicator of future effects on life history.

(1)H NMR-based metabolomics investigation of Daphnia magna responses to sub-lethal exposure to arsenic, copper and lithium

Metal and metalloid contamination constitutes a major concern in aquatic ecosystems. Thus it is important to find rapid and reliable indicators of metal stress to aquatic organisms. In this study, we tested the use of (1)H nuclear magnetic resonance (NMR) - based metabolomics to examine the response of Daphnia magna neonates after a 48h exposure to sub-lethal concentrations of arsenic (49μgL(-1)), copper (12.4μgL(-1)) or lithium (1150μgL(-1)). Metabolomic responses for all conditions were compared to a control using principal component analysis (PCA) and metabolites that contributed to the variation between the exposures and the control condition were identified and quantified. The PCA showed that copper and lithium exposures result in statistically significant metabolite variations from the control. Contributing to this variation was a number of amino acids such as: phenylalanine, leucine, lysine, glutamine, glycine, alanine, methionine and glutamine as well as the nucleobase uracil and osmolyte glycerophosphocholine. The similarities in metabolome changes suggest that lithium has an analogous mode of toxicity to that of copper, and may be impairing energy production and ionoregulation. The PCA also showed that arsenic exposure resulted in a metabolic shift in comparison to the control population but this change was not statistically significant. However, significant changes in specific metabolites such as alanine and lysine were observed, suggesting that energy metabolism is indeed disrupted. This research demonstrates that (1)H NMR-based metabolomics is a viable platform for discerning metabolomic changes and mode of toxicity of D. magna in response to metal stressors in the environment.