Helpful parasites in polluted environments – HELP

Freshwater pollution, especially by pesticides and pharmaceutical residues, raises growing concern for human and environmental health. Some chemical compounds are of great concern, due to their ubiquity and toxicity. Among them, imidacloprid, a neonicotinoid insecticide, and diclofenac, a nonsteroidal anti-inflammatory drug are sadly notorious for their impacts on biodiversity. Objective risk-assessments are a major and challenging task and require studying the eco-dynamics of pollutants, i.e. their fate in aquatic ecosystems, and their ecotoxicological effects in interaction with other environmental pressures. The role of parasites in the transfer, metabolization and accumulation of pollutants has been neglected so far. Some parasites, such as acanthocephalans, have the remarkable ability to sequester contaminants from their host. In turn, infected organisms are less contaminated than uninfected ones. Indirect benefits of parasitism have been highlighted in contaminated environments: hosts exhibit lower levels of oxidative stress, better body condition, and higher survival rate. These results challenge the traditional view of parasitism as an additional stress factor, with an exacerbation of damages induced by contaminants and parasites. We expect that environmental pollution could shape the strength and direction of host-parasite interactions, when the costs of parasite infection (pathogenicity) are outweighed by the benefits of pollutant sequestration. This project aims to test whether the environmental contamination can shift parasitism to mutualism. The effects of exposure to imidacloprid and diclofenac at different levels will be investigated on the well-studied chub - acanthocephalan model. The first objective is to understand the effect of these pollutants and their metabolites on parasites, by evaluating the potential damages on the fitness of acantocephalans, in terms of development and reproduction rate. The use of micro-endoscopy will be developed. The second objective is to study the joint effects of parasite load and pollutants exposure on chubs across levels of biological organization: we will monitor molecular, physiological and behavioral alterations, as well as dysbiosis of the intestinal microbiota, in terms of composition, diversity and functionality. Experimental infestations with acanthocephalans and chronic exposure to pollutants via slow-release implants will be conducted in semi-natural and natural conditions (aquatic mesocoms, at the CEREEP-Ecotron experimental platforms, and in situ through populations monitoring). Integrative approaches and innovative tools will be deployed. This project is built on synergies and cross-fertilisation between complementary disciplines, such as ecotoxicology, ecophysiology, behavioral ecology, chemistry and microbiology, host-parasite interactions, population biology. This project will involve different research laboratories, as well as students (university projects) and volunteers (participative science).