Résumé
Mercury pollution is ubiquitous and known for its high toxicity. This contaminant bioaccumulates through the trophic chain, and can pose a significant threat for organisms once levels reach specific thresholds. This pollution is especially problematic in aquatic environments, where mercury is methylated by aquatic microorganisms into methylmercury MeHg, its most dangerous form. Although much work has focused on the impacts of MeHg on vertebrate organisms, little is known about its effects on the organisms that live in association with these species, and in particular, their parasites. Our study experimentally investigated the effects of methylmercury (MeHg) contamination of host blood on the development and reproduction of soft ticks (Family Argasidae ; genus Ornithordoros). We considered two species, Ornithordoros (Alectorobius) maritimus collected from natural populations of its seabird host – Larus michahellis, and a laboratory population of O. moubata. Ticks were artificially fed with blood containing five different methylmercury concentrations, defined from field based levels present in L. michahellis (0, 0.76 μl/ml, 3.8 μl/ml,7.6 μl/ml, 38 μl/ml). At the highest concentration, juvenile ticks were unable to moult and died within a few days. No other effects at the other concentrations were found after a single bloodmeal, suggesting that ticks may either have high tolerance to this contaminant or are able to excrete it during blood digestion. More detailed and longer term studes are now required to evaluate more subtle impacts of MeHg contamination on tick life history traits, and the potential consequences this may have for the transmission dynamics of tick-borne disease.