Abstract
Living organisms most often face multiple stressors in natural environments. However, the cumulative effects of multiple stressors, acting synergistically or antagonistically on species and ecosystems, remain poorly appreciated. In particular, the combined effect of parasites with abiotic stressors deserves particular attention, at a time where anthropogenic stress and climate change appear to be two major causes of parasitic diseases emergence in natural populations. The existing literature suggests that the interaction between parasitic or pathogenetic organisms and abiotic stressors is a complex one. Furthermore, the interactions between parasitic infections and abiotic stressors may have far-reaching and subtle consequences in ecosystems. For example, given the role of trophically-transmitted parasites as ecosystem engineers, any impact of stressors on host-parasite associations can have cascade effects throughout the entire food web. /nGammarid amphipods represent, in many freshwater communities, the dominant macroinvertebrate species in terms of biomass. As detritivores and scavengers, they play a central role in freshwater ecosystems. Their distribution is influenced by abiotic factors such as temperature, salinity, oxygen, acidity and pollution. Amphipods are considered to be a good and robust biomonitor of the quality of freshwater ecosystems, and the effect of contaminants or other abiotic stresses begins to be very well documented. Parallel to this, gammarids are known to be infected by acanthocephalans, a widespread group of trophically-transmitted parasites, for which they are intermediate hosts. The influence of acanthocephalans on the physiology and behaviour of their amphipod hosts has been largely documented as well. However, the effect of interactions between these biotic stressors and the abiotic ones remains poorly documented. The present project aims at studying i) how macroparasites interact with abiotic stressors such as thermal stress and contaminants in affecting the physiology and behaviour of the freshwater amphipod Gammarus pulex and ii) their functional role in freshwater ecosystems, and iii) to investigate to what extent genetic variability between and within populations is involved in the ability of individuals to cope with multiple stressors. Given the crucial ecosystemic role played by amphipod species, the results of the project are likely to increase our understanding of the predictable dynamics of the quality of freshwater ecosystems exposed to global change and increasing anthropic pressure.
France