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.

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The in situ feeding bioassay in Gammarus fossarum is recognized as a reliable tool for monitoring the toxicity of freshwater contamination. However, whether recorded feeding inhibitions can potentially provoke population-level adverse outcomes remains an open question. In the present study, the authors present an experimental study in G. fossarum, which contributes to the quantitative description of the links between feeding inhibitions and impacts on female reproductive performance. The authors studied the impacts of food deprivation on reproductive endpoints (i.e., fecundity, fertility, molt cycle) during 2 successive molting cycles. Among the main results, the authors found that food deprivation triggered a slowdown of the molting process and a reduction in fertility but no alteration to embryonic development. These reproductive impairments appeared for feeding inhibition values usually recorded in monitoring programs of environmental pollution. Using a population model translating Gammarus life-history, the authors predicted that the observed reproductive alterations predict a strong degradation of population dynamics. The present study underlines the importance of feeding inhibition in population-level risk assessment and discusses how establishing upscaling schemes based on quantitative mechanistic links between impacts at different levels of biological organization can be applied in environmental monitoring to propose an ecotoxicological assessment of water quality, which would be sensitive, specific, and ecologically relevant.