Meeting Abstract
An individual’s investment in constitutive immune defenses depends on both endogenous and exogenous factors. We examined how population, Leucocytozoon parasite presence, mass scaled for structural size, heterophil:lymphocyte (H:L) ratio, and age affected immune defenses in golden eagle (Aquila chrysaetos) nestlings from California, Oregon, and Idaho. We quantified hemolytic-complement activity and bacterial killing ability, two constitutive measures of complement activity. Scaled mass and age did not affect immune defenses. Eagles with lower H:L ratios had lower complement activity, collaborating other studies that found that animals in better condition sometimes invest less in constitutive immunity. Results for Leucocytozoon presence indicate that eagles with infections had higher concentrations of circulating complement proteins but not elevated antibodies for all microbes. In addition, eagles from OR had significantly higher constitutive immunity than those from CA or ID. We posit that OR eagles might have elevated immune defenses because they are exposed to more parasites than eagles from CA or ID. Although we have incomplete data on parasite exposure for our populations, our suggestion is supported by the observation that bacteria-killing ability was higher when Leucocytozoon were present. By focusing on a free-living, long-lived raptor species, rather than more commonly studied passerines, our study helps develop a broad perspective regarding the evolutionary and environmental pressures on immune function in birds.
