Multistress Gammarus fossarum

Using a fully crossed factorial design, we investigated the behavioral and physiological responses of the amphipod Gammarus fossarum to acute exposure methomyl insecticide, in interaction with infection and temperature. Infection with the acanthocephalan Pomphorhynchus tereticollis was taken into account at both the population level (uninfected gammarids from populations hosting the parasite -non -naïve- or not -naïve-) and the individual level (infected and uninfected gammarids).
Following four-days acute exposure to methomyl at 12°C and 16°C, we recorded individual survival, food intake, locomotor activity and sheltering behavior. We quantified several whole-individual biomarkers, including non-specific defense systems (antioxidant, phenoloxidase, GlutathionS-transferase), oxidative damage, and acetylcholinesterase.
Overall, additive effects between stressors prevailed, with fewer interactive and antagonistic ones. Methomyl and temperature alone had limited effect, while parasitism had pervasive effects on most traits at both individual and population levels. Our study adds to a growing body of evidence on the importance of parasitism in ecotoxicological studies.