Consequences of immunosenescence in the wild: A field experiment in tree swallows.

PALACIOS, M. G.; WINKLER, D. W.; VLECK, C. M.

Boston, Massachussetts, EEUU

Congreso; Annual Meeting of the Society for Integrative and Comparative Biology.; 2009

Society for Integrative and Comparative Biology.

Aging is a pervasive phenomenon in free-living organisms, but its consequences in the wild are remarkably understudied. We previously showed that free-living tree swallows experience immunosenescence. We investigated the consequences of this aging pattern by testing the hypothesis that older, immunosenescent individuals suffer higher costs of defense against pathogens than younger ones. We performed a field experiment to determine age-specific responses of adult female tree swallows to a simulated pathogenic insult (challenge with bacterial lipopolysaccharide, LPS) and carried out an integrated assessment of sickness behavior, hormonal changes, and immune function. In addition, we assessed the consequences of parental responses on current and future reproductive success and survival. Preliminary analyses indicate that in support of our hypothesis, when challenged with LPS, older, immunosenescent females suffered increased sickness behavior compared to younger ones, reflected by larger loss of body mass and decreased nest visitation rate. In contrast, bacterial killing capacity of plasma increased after LPS challenge but not in an age-specific manner. Moreover, baseline corticosterone was not affected by LPS nor did it differ with female age. Nestlings of LPS females showed increased corticosterone and reduced growth, but this was also independent of female age. Because some of these results are year-dependent we are assessing the influence of potential covariates (e.g., insect availability and weather) on observed responses. Additionally, we are currently analyzing other response variables of females (e.g., natural antibodies, complement-mediated lysis, specific antibodies against LPS, and H/L ratios), as well as reproductive and survival parameters.