The epidemiology of infectious diseases, and especially of emerging and re-emerging diseases, can benefit from evolutionary and ecological approaches, notably when they deal with the mechanisms of host response to parasitism. A response to parasitism like the transfer of antibodies from mother to offspring has also broad potential implications in evolutionary ecology, from the adaptive value of maternal effects to the role of transgenerational plasticity in host-parasite interactions. Recent contributions have addressed key issues such as environmental factors affecting the amount of antibodies transferred and whether maternal antibodies affect offspring immunity, but little is still known about factors driving the evolution of the maternal transfer of antibodies and its eco-epidemiological implications. In the current project, we propose to extend our previous work on this topic by addressing a series of key related issues. To do so, we will use complementary approaches, from theory to field and laboratory experiments. The first objective (Task 2) will be to develop theoretical approaches on the evolutionary issues and epidemiological implications of the maternal transfer of antibodies. This will allow us to investigate feedback loops between ecological and evolutionary processes, notably in relation to the dynamics of parasite transmission within host populations. Second, we will investigate predictions about among and within-species variability in traits related to the transfer of maternal immunity, namely the rates of transfer of antibodies and the temporal persistence of antibodies in the offspring. Recent results we obtained show that strong variability among species exists for at least one of these traits. The potential genetic basis of the transfer of maternal antibodies and its associated potential costs will be investigated by developing a selection experiment with poultry (with the possibility to assess correlated responses to selection on the propensity to transmit antibodies while controlling statistically for the mother capacity to produce antibodies) (Task 3). Third, we will ask whether specific benefits of the transfer of maternal antibodies occur in natural situations (Task 4). This will be done by using a novel approach (the injection of antibodies into the egg yolk) to specifically address the potential protective effects of maternal antibodies in a natural host-parasite system involving the kittiwake gull Rissa tridactyla, seabird tick Ixodes uriae and Lyme disease agent Borrelia burdgorferi s.l. Finally, we will address how social interactions and spatial structure can empirically affect the relationships between disease agent circulation and maternal antibody transfer (Task 5). This will be done by conducting a specific experiment on allosuckling and maternal antibody transmission in a social mammal, and by investigating factors affecting the prevalence of eggs containing antibodies against zoonotic agents in spatially structured populations of wild birds. Overall, the expected results could have important basic implications on the evolutionary ecology of host-parasite interactions, but could also lead to interesting applications in terms of immuno-therapeutics, poultry production, eco-epidemiology and conservation.