Meeting Abstract
P1.155 Sunday, Jan. 4 Are the immune systems of tropical birds glucocorticoid resistant? ALAM, J. L.*; LIEBL, A.L.; MARTIN, L.B.; FOKIDIS, H.B.; University of South Florida; University of South Florida; University of South Florida; Arizona State University jalam@mail.usf.edu
Corticosterone alters immune function, but its effects vary depending on magnitude and duration, immune response characterized, species studied, and environmental context. In a previous study, we found that a cutaneous inflammatory response was not affected by chronically elevated corticosterone in house sparrows (Passer domesticus) from Panama but similar corticosterone elevation in birds from New Jersey (USA) reduced the same immune response. This differential sensitivity to corticosterone, coupled with a more persistent threat of infection in the Panamanian population, led to the hypothesis that tropical birds generally may decouple stress hormones from immune responses to maximize immune defense at all times. To test this hypothesis, we conducted an experiment on different tropical (Kenya) and temperate (Arizona) populations of house sparrows. This time, however, we compared the effects of 30 minutes in a cloth bag on the capacity of plasma to kill gram-negative bacteria (E. coli) to determine whether i) other tropical house sparrows are immunologically resistant to corticosterone; ii) acute (versus chronic) stress differentially affects immune function depending on latitude; and iii) stress affects other components of house sparrow immunity. Corticosterone release in response to the stressor was lower in Kenyan than Arizonan birds, but much less so than in the prior study. Further, bactericidal capacity of blood was not affected by acute stress in either population, and Arizonan sparrows killed almost all bacteria while Kenyan sparrows killed almost none. Collectively these results indicate population differences in immune and endocrine physiology, but not in the manner predicted. Ongoing studies of these and other sparrow populations are testing whether patterns are better explained by invasion history than latitude.
