Interannual dynamics of antibody levels in naturally infected long-lived colonial birds.

Little is known about the long-term persistence of specific antibodies (Ab) in natural host-parasite systems despite its potential epidemiological and ecological importance. In long-lived species, knowledge of the dynamics of individual immunological profiles can be important not only for interpreting serology results, but also for assessing transmission dynamics and the potential selective pressures acting on parasites. The aim of this paper was to investigate temporal variation in levels of specific Ab against the bacterium Borrelia burgdorferi sensu lato in adults of a long-lived colonial seabird, the Black-legged Kittiwake Rissa tridactyla. In wild populations, adults are naturally exposed each breeding season to a Borrelia vector, the tick Ixodes uriae. Breeding birds were captured during four consecutive breeding seasons, and parasite infestation quantified. Using enzyme-linked immunosorbent assay (ELISA) and immunoblots, we found that the immunological profiles of anti-Borrelia Ab were highly repeatable among years, reflecting the interannual persistence of Ab levels. We nevertheless also observed that year-to-year changes of Ab levels were related to exposure to ticks in the previous year. The long-term persistence of Ab levels may be an important mechanism of individual protection against future exposure to the microparasite. It will also affect the availability of susceptible hosts, and thus the transmission dynamics of the bacterium. These results illustrate the need to consider the dynamics of the immune response in order to better understand the evolutionary ecology of host-parasite interactions in natural populations.