Does exposure to zinc, methomyl, and perfluorooctanoic acid alter feeding behavior on MUG® in the freshwater amphipod <i>Gammarus fossarum</i>?

Feeding rate alteration is one of the first observed responses when animals are exposed to toxic stress and is recognized as a relevant tool for studying chemical compounds toxicity. However, food substrates that are currently used for ecotoxicity tests are not always easily available compared with referenced products. Using the European freshwater amphipod Gammarus fossarum, we here propose a standardized food substrate fabricated with referenced ingredients: the MUG® (meal unit for gammarid) for ecotoxicity tests. To investigate the suitability of using MUG to study behavioral response of amphipods to toxic stress, in laboratory-controlled conditions, we explored whether three chemical compounds belonging to different families of contaminants (zinc [Zn], a metal; methomyl [MT], an insecticide; and perfluorooctanoic acid [PFOA], a per-/poly-fluoroalkyl substance) could affect gammarids feeding rates on MUG. First, we explored the effects of 7-day exposure to different concentrations of each contaminant alone. Although PFOA did not affect feeding rate, Zn induced feeding behavior on MUG at a lower concentration but inhibited food consumption at higher ones, whereas MT 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 with the control group. Observed effects of binary mixtures were also compared with predicted values based on additive effects of contaminants. Both Zn/MT and Zn/PFOA mixtures inhibited feeding behavior compared with predictions, resulting in feeding rate values similar to controls. Overall, our study supports that MUG represents a promising standardized food substrate for evaluating substance effects on amphipod behavior during laboratory ecotoxicological bioassays.