Abstract
Biological invasions are increasingly phenomenon worldwide having deleterious impacts on biodiversity and human health. Studying the mechanisms explaining them allows both (i) to define efficient strategies for controlling and preventing invaders and (ii) to study ecological and evolutionary processes at contemporary scales. Some major hypotheses rely on parasitism and host immunity to explain invasion success. Thus, exotic host populations (1) may benefit of an " Enemy Release " (ER) through impoverishment of their original parasite communities, and may affect native hosts by (2) transferring exotic parasites (Spill-Over, SO) and/or (3) by increasing transmission risk of native parasites (Spill-Back, SB). In turn, according to the refined “Evolution of Increased Competitive Ability” (EICA) theory, invasive populations should experience immune trade-offs by favouring less expensive antibody-mediated responses over costly inflammation, to increase their competitive ability (dispersion, reproduction). The aim of my thesis is to test these predictions along the invasion routes of two commensal exotic species in Senegal, the domestic mouse (Mus musculus domesticus) and the black rat (Rattus rattus). These rodent species are considered to be major invasive species worldwide inducing high economic, sanitary and ecological damages. My research is based on comparative analyses along one invasion route for each invasive species. We focused on gastrointestinal helminths and pathogenic bacteria as parasite communities, and inflammation and natural antibody-mediated responses as immune estimates. Comparisons were performed for invasive and/or native (Mastomys spp.) rodents between localities of long-established invasion (100-200 years ago), recent invasion (10-30 years ago; invasion front), and non-invaded localities. My findings showed variations along both invasion routes in parasite community structure and immune patterns, but in a more complex way than expected under the initial predictions. The heterogeneity of changes observed highlights the existence of particular relations between host and parasite traits, host immune investment, environmental conditions and biological invasions. Further experimental works are needed to assess the consequences and mechanisms underlying the changes observed along both invasion routes.