Gammarids are amphipods found worldwide distributed in fresh and marine waters. They play an important role in aquatic ecosystems and are well established sentinel species in ecotoxicology. In this study, we sequenced the transcriptomes of a male individual and a female individual for seven different taxonomic groups belonging to the two genera Gammarus and Echinogammarus: Gammarus fossarum A, G. fossarum B, G. fossarum C, Gammarus wautieri, Gammarus pulex, Echinogammarus berilloni, and Echinogammarus marinus. These taxa were chosen to explore the molecular diversity of transcribed genes of genotyped individuals from these groups. Transcriptomes were de novo assembled and annotated. High-quality assembly was confirmed by BUSCO comparison against the Arthropod dataset. The 14 RNA-Seq-derived protein sequence databases proposed here will be a significant resource for proteogenomics studies of these ecotoxicologically relevant non-model organisms. These transcriptomes represent reliable reference sequences for whole-transcriptome and proteome studies on other gammarids, for primer design to clone specific genes or monitor their specific expression, and for analyses of molecular differences between gammarid species.

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Deciphering evolutionary processes occurring within long-term contaminated wild populations is essential for the ecological risk assessment of persistent chemical contaminations. Using field populations of Gammarus, a commonly-used genus in aquatic ecotoxicology, the present study sought to gain insights into the extent to which long-term exposure to metals in the field could effectively lead to shifts in toxicological sensitivities. For this, we identified a Gammarus population inhabiting a stream contaminated by cadmium (Cd). We compared the Cd-exposure and Cd-sensitivity of this population to those of five reference populations. Active biomonitoring determined in different years and seasons that significant levels of Cd were bioavailable in the contaminated site. Laboratory sensitivity tests under common garden conditions established that this long-term field exposure led to the development of a moderate Cd tolerance, which was maintained after a 3-week acclimatization in the laboratory, and transmitted to offspring produced under clean conditions. The potential physiological costs of tolerance were assessed by means of feeding rate measurements (in the laboratory and in situ). They revealed that, unlike for reference populations, the feeding activity of organisms from the tolerant population was greatly decreased when they were maintained under laboratory conditions, potentially indicating a high population vulnerability to environmental perturbations. Because dissolved Cd concentrations in water from the contaminated site were low (averaging 0.045 µg L(-1)) and below the current European environmental quality standard for Cd for inland surface waters (fixed at 0.08 µg L(-1) in soft water environments), this case study sheds light onto the extent to which current environmental quality standards are protective against potential adverse outcomes of adaptive and micro-evolutionary processes occurring in contaminated environments.

As a proof of principle, a selected reaction monitoring (SRM) mass spectrometry-based methodology was applied to the simultaneous quantification of dozens of protein biomarkers in caged amphipods (Gammarus fossarum). We evaluated the suitability of the methodology to assess complex field contaminations through its application in the framework of a regional river monitoring network. Thanks to the high throughput acquisition of biomarker levels in G. fossarum exposed in four reference and 13 contaminated sites, we analyzed the individual responses of 38 peptides reporting for 25 proteins of interest in 170 organisms. Responses obtained in contaminated sites included inductions of vitellogenin-like proteins in male organisms, inductions of NaK/ATPases, and strong inhibitions of molt-related proteins such as chitinase and JHE-carboxylesterase. Proteins from detoxification and immunity processes were also found modulated in abundance. Summarizing, the results presented here show that the SRM strategy developed for multibiomarker measurement paves a very promising way to define multiple indicators of the health status of sentinel organisms for environmental hazard assessment.