Contemporary variations of immune responsiveness during range expansion of two invasive rodents in Senegal

Abstract : Biological invasions provide unique opportunities for studying life history trait changes over contemporary time scales. As spatial spread may be related to changes in parasite communities, several hypotheses (such as the evolution of increased competitive ability (EICA) or EICA-refi ned hypotheses) suggest immune changes in invasive species along invasion gradients. Although native hosts may be subject to similar changes in parasite selection pressures, their immune responses have been rarely investigated in invasion contexts. In this study, we evaluated immune variations for invasive house mice Mus musculus domesticus , invasive black rats Rattus rattus and native rodents Mastomys erythroleucus and Mastomys natalensis along well-characterised invasion gradients in Senegal. We focused on antibody-mediated (natural antibodies and complement) and infl ammatory (haptoglobin) responses. One invasion route was considered for each invasive species, and environmental conditions were recorded. Natural-antibody mediated responses increased between sites of long-established invasion and recently invaded sites only in house mice. Both invasive species exhibited higher infl ammatory responses at the invasion front than in sites of long-established invasion. Th e immune responses of native species did not change with the presence of invasive species. Th ese patterns of immune variations do not support the EICA and EICA refi ned hypotheses, and they rather suggest a higher risk of exposure to parasites on the invasion front. Altogether, these results provide a fi rst basis to further assess the role of immune changes in invasion success.