Abstract: Keynote talk in the Symposium 'HOST-PARASITE INTERACTIONS IN SEABIRDS: EVOLUTIONARY ECOLOGY AND ECO-EPIDEMIOLOGICAL ISSUES' (organized by Thierry BOULINIER & Sarah BURTHE) of the 2nd World Seabird Conference, Cape Town, South Africa, October 2015.
Abstract: Nest ectoparasites are common components of the seabird breeding environment whose presence can have major consequences for seabird reproductive success and population dynamics. Ticks are among the most frequent parasite inhabitants of seabird colonies and are known to have direct major impacts on the birds when infestations are high, as well as indirect effects via the transmission of infectious agents. As seabirds show strong seasonality in colony attendance and these parasites are temporary, associated with the host only during the bloodmeal, ticks have evolved well-adapted life history strategies to successfully exploit both their biotic (seabird) and abiotic (colony) environments. However, different seabird species frequently breed within the same colony, setting up an interesting dilemma for a parasite: specialize to exploit a single host type, or remain a generalist and exploit less well each host type ? In this talk, I address this question by focusing on work that we have carried out on a model system involving a ubiquitous seabird ectoparasite, the tick Ixodes uriae, which has a bipolar distribution. I present patterns of contemporary population genetic structure of this tick at the within-colony scale from distinct regions of its worldwide distribution and link this structure to phenotypic patterns of host-associated specialisation. As this tick transmits an array of vector-borne disease agents, including human Lyme disease bacteria, I follow up with a discussion on how adaptation to the seabird host may cascade down to alter the epidemiology and evolutionary pathway of tick-borne microparasites. Finally, I will outline how comparative studies that we are currently developing with another widespread seabird tick, the soft tick Carios capensis, should shed further light on cascading effects of vector ecology and evolution on the circulation of tick-borne agents at broad geographic scales.