Does exposure to zinc, methomyl and perfluorooctanoic acid alter feeding behaviour on MUG® in the freshwater amphipod Gammarus fossarum?

Abstract

Feeding rate alteration is one of the first observed responses when animals are exposed to toxic stress and recognized as relevant tool for studying chemical compounds toxicity. However, food substrate that are currently used for ecotoxicity tests are not always easily available compared to referenced products. Using the European freshwater amphipod Gammarus fossarum, we here proposed for ecotoxicity tests a standardized food substrate fabricated with referenced ingredients: the MUG® (Meal Unit for Gammarid). To investigate the suitability of using MUG® to study behavioural response of amphipods to toxic stress, we explored in laboratory-controlled conditions whether three chemical compounds belonging to different families of contaminants (zinc (Zn): metal; methomyl (MT): insecticide; perfluorooctanoic acid (PFOA): Per-/poly-fluoroalkyl substance (PFAS)) could affect gammarids feeding rates on MUG®. First, we explored the effects of 7-day exposure to different concentrations of each contaminant alone. While PFOA did not affect feeding rate, zinc induced feeding behaviour on MUG® at lower concentration but inhibited food consumption at higher ones, whereas methomyl decreased feeding rate with increased concentration. Then, we explored effects when gammarids were exposed during 7 days to mixtures of molecules in pairs. No effect of mixtures was observed on MUG® consumption compared to control group. Observed effects of binary mixtures were also compared to predicted values based on additive effects of contaminants. Both Zn/MT and Zn/PFOA mixtures inhibited feeding behaviour compared to predictions, resulting in feeding rate values similar to control ones. Overall, our study supports that MUG® represent a promising standardized food substrate for evaluating substances effects on amphipods behaviour during laboratory ecotoxicological bioassays.