title: Infection risk dictates immunological divergence among populations in a Mediterranean lizard.
abstract: The ability of vertebrates to evolve different defence strategies in response to varying parasitism regimes remains poorly understood. Hosts may adopt two different strategies to defend themselves against parasites: tolerance (hosts alleviate the negative fitness consequences of parasite infection) and resistance (hosts strengthen their immune response as parasite burden increases). Both strategies are effective, but fitness has been reported to decline faster in less-tolerant individuals. Here, we assessed the number of splenocytes and the cell-mediated response (proxies for resistance) and body condition (a proxy for tolerance) in four populations of a Greek endemic lizard (Podarcis gaigeae), each exposed to different infection risks (defined as the cumulative effect of parasite burden and duration of exposure). We anticipated that populations with heavy parasite burden would enhance the efficacy of their immune response (resistance) compared to lizards deriving from parasite-poor habitats. We also predicted that populations with longer exposure to parasites would be adopted and be more tolerant. Each factor (duration of exposure and parasite burden) had a distinct effect on the immune response, and thus, our results were rather complicated. Lizards with heavy parasite burden and aperiodic exposure demonstrated resistance, whereas lizards with heavy parasite burden and chronic exposure were more tolerant. Populations with low parasite burden and minimal exposure were more resistant. Our results suggest that the development of some immunological strategies may be differentiated under different infection risks, even within the same species.
authors.affiliation: Department of Human and Animal Physiology, Faculty of Biology, National and Kapodistrian University of Athens, Athens, Greece. ksagonas@biol.uoa.gr.
authors.forename: K
authors.initials: K
authors.lastname: Sagonas
authors.affiliation: Department of Human and Animal Physiology, Faculty of Biology, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: I A
authors.initials: IA
authors.lastname: Rota
authors.affiliation: Department of Human and Animal Physiology, Faculty of Biology, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: O E
authors.initials: OE
authors.lastname: Tsitsilonis
authors.affiliation: Department of Zoology and Marine Biology, Faculty of Biology, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: P
authors.initials: P
authors.lastname: Pafilis
authors.affiliation: Department of Human and Animal Physiology, Faculty of Biology, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: E D
authors.initials: ED
authors.lastname: Valakos
mesh_terms: D000818:Animals; D004777:Environment; D006115:Greece; D007109:Immunity; D008116:Lizards / Q000276:immunology / Q000469:parasitology*; D010271:Parasites
keywords: cell-mediated response; immune resistance; immune tolerance; island; mixed lymphocyte reaction; reptiles