Parasite diversity: an overlooked metric of parasite pressures?

Abstract

Most free-living animals in their natural environments are hosts for a large diversity of parasites at individual, population or species level. Ongoing global changes are dramatically affecting the structure of the parasite diversity hosts may face, mostly through the alteration of the geographical distributions of parasites in relation to climate change, habitat fragmentation or bioinvasions (Daszak et al. 2000). Hosts are facing new parasites, which gives rise to the building of new communities of parasite species. In the face of these novel and increased risks of exposure to new parasites, it becomes crucial to improve our knowledge about the cumulative effects of co-infections on various host traits. Emphasizing the importance of polyparasitism in host populations could also improve our knowledge about the role of parasitism in ecosystems (Kuris et al. 2008). Host parasite interactions have been intensively investigated mostly on single host species/single parasite species, whereas hosts are typically infected by multiple parasite species. After emphasizing the importance of parasite diversity in natural populations, we focus on mammals and discuss the main limits of ‘one host/one parasite system’ approaches when estimating parasitic pressures. Then, we give recent arguments that support the hypothesis that parasite diversity per se exerts a strong selective pressure on hosts. We also discuss some inherent problems concerning the estimation of this potential underestimated metric of parasite pressures. Finally, we propose several directions to progress in our knowledge on the effects of parasitic pressures in natural systems.