Consideration of inter-population variability to improve ecological relevance of biomarkers

Among freshwater species intensively used in ecotoxicology, Gammarus fossarum is a relevant test species. In addition to its sensitivity towards contaminants, this species is a common shredder which plays a major role in leaf litter breakdown processes. Many sub-individual and individual responses have been proposed in gammarids in order to monitor and predict effects of chemical compounds on water quality. In this framework, energetic metabolism variations appear to be a good predictive tool to detect physiological disturbance of organisms linked to ecosystem quality. Indeed animal survival depends on the availability of metabolic energy necessary to ensure maintenance, growth and reproduction. Among biological processes to access energy, digestive capacities appear sensitive to contamination stress. In recent studies, based on the use of one reference population, reference and threshold values for digestive enzymes proposed as biomarkers were defined. In the same way, the same research team described link between digestive changes and reproductive impairments. So digestive capacities appear as potential ecologically relevant endpoints to provide information on the consequences likely to occur at the highest hierarchical levels of organization (population). However the use of only one experimental population is not representative of biological diversity. In this way, it appears necessary to precise the between-population variability of these enzyme activities. Among more than 40 sites investigated, 8 populations of Gammarus fossarum considered as reference were selected. On these populations a double approach was applied. In a first step, the basal level of digestive enzyme activities were studied after an acclimation of organisms to similar laboratory conditions. In a second step, the pattern of digestive capacities modulation in the 8 poulations exposed at a similar stress (trophic stress) were considered. This second step aims to identify a potential difference of sensitivity between the eight populations. The results of this preliminary study, underlying changes in digestive enzymes activities, will be discussed according to environmental parameters which could be implied (different sources of food according to the site) but also concerning the potential consequences on the reference and threshold values define previously via one control population.