Project description:Chemical contamination is a common threat to biota thriving in estuarine and coastal ecosystems. In particular, trace metals tend to accumulate and exert deleterious effects on small invertebrates such as zooplankton, which are essential trophic links between phytoplankton and higher-level consumers in aquatic food webs. Beyond the direct effects of the contamination, we hypothesized that metal exposure could also affect the zooplankton microbiota, which in turn might further impair host fitness. To assess this assumption, copepods (Eurytemora affinis) were sampled in the oligo-mesohaline zone of the Seine estuary and exposed to dissolved copper (25 µg.L-1) over a 72-hour time period. Copepod response to copper treatment was assessed by determining transcriptomic changes in E. affinis along with shifts in its microbiota. Unexpectedly, very few genes were differentially expressed in copper-treated copepods compared to controls, with most of the reported differences involving genes upregulated in males compared to females. In contrast, copper increased the taxonomic diversity indices of the microbiota and resulted in substantial compositional changes at both the phyla and genus levels. Phylogenetic reconstruction of the microbiota further suggested that copper mitigated phylogenetic relatedness of taxa at the basal tree structure of the phylogeny, whereas it strengthened it at the terminal branches. Increased terminal phylogenetic clustering in copper-treated copepods concurred with higher proportions of bacterial genera previously identified as copper resistant (e.g., Pseudomonas, Acinetobacter, and Alkanindiges) and a higher relative abundance of the copA gene encoding a periplasmic inducible multi-copper oxidase. Overall, these results revealed very contrasting responses of E. affinis and its microbiota to copper exposure. The enrichment in micro-organisms likely to perform copper sequestration and/or enzymatic transformation processes, underlines here the need to follow the microbial component during the evaluation of the vulnerability of the zooplankton to the metallic stress.
Project description:Copepods are zooplanktonic crustaceans ubiquitously widespread in aquatic systems. They are of ecological importance due to their place in the trophic chain. Copepods are exposed to a wide variety of pollutants as insect growth regulators (IGR) acting as endocrine disruptors although they are not the target. The aim of the present work was to investigate the molecular response of a non-targeted organism, the copepod Eurytemora affinis, to an IGR. Adult males and females were exposed at two sub-lethal concentrations of tebufenozide (TEB), an agonist of the ecdysone receptor targeting lepidopteran larvae. Results suggest a gender-specific response with a higher sensitivity in males potentially due to a differential activation of stress response pathways. Indeed, genes coding for proteins involved in stress response were mis-regulated in males while not in females suggesting that detoxification processes are still ongoing in males. In both genders, TEB exposure triggers similar pathways as for its targeted species by modulating the transcription of early and late ecdysone responsive genes. Among them, genes involved in cuticle metabolism, muscle contraction, neurotransmission and gametogenesis whose mis-regulation could lead to moult, locomotor and reproductive impairments. Furthermore, genes coding for proteins playing part in epigenetic processes were found in both genders highlighting the potential impact of TEB exposure on further generations. Beyond the in-depth knowledge of the molecular MoA of an ecdysone agonist on a non-targeted organism, this work provides data allowing the identification of (i) potential biomarkers of ecdysone agonists and (ii) putative physiological responses to be further assessed to characterize the effects of TEB at higher biological levels. The present study reinforces the suitability of the use E. affinis as an ecotoxicological model.
Project description:Compared to freshwater ecosystems, the health status of estuarine waters remains little studied despite their importance for many species. They also represent a zone of interest for Human settlements that make them the final sink of pollution in both the water column and sediment. Once in sediments, pollutants could represent a threat to benthic as well as pelagic estuarine species through resuspension events. In the Seine estuary, the copepod Eurytemora affinis has been previously presented as a relevant species to assess resuspended sediment contamination through the use of fitness-related effects at the individual level. The aim of the present study was to use E. affinis copepods to assess estuarine sediment-derived elutriates toxicity using both a molecular (i.e. transcriptomics) and a behavioral approach. Two sites along the Seine estuary were sampled. They were both under anthropic pressures from the industrial-port activities or wastewater treatment plants (i.e. Tancarville) or agricultural pressure from freshwater affluent (i.e. Fatouville). The analysis of sediments used to prepare elutriates reveals that both sites have close contamination profiles. The transcriptomic analysis reveals that exposure to both sites triggers the dysregulation of genes involved in biological function as defense response, immunity, ecdysone pathway or neurotoxicity. This analysis also reveals a higher count of dysregulated genes in the Fatouville site compared to the Tancarville despite their close contamination profile. These results emphasize the sensitivity of this molecular approach to assess environmental matrix toxicity with E. affinis. The analysis of the swimming behavior of E. affinis did not highlight significant effects after both sites elutriate exposure. However, our strategy to assess E. affinis swimming behavior (i.e the combination of the DanioVision observation chamber and the EthoVision analysis software) allows the discrimination of basal swimming behavior in this species. Thus, it represents a promising standardized tool to assess copepods swimming behavior in ecotoxicological studies.