Meeting Abstract

P1.76  Tuesday, Jan. 4  Seasonal, sex and age differences in immune function and corticosterone in Red-winged Blackbirds (Agelaius phoeniceus) MERRILL, L.**; ROTHSTEIN, S.I.*; O’LOGHLEN, A.L.*; WINGFIELD, J.C.*; University of California, Santa Barbara; University of California, Santa Barbara; University of California, Santa Barbara; University of California, Davis lmerrill@lifesci.ucsb.edu

If resources are limiting, organisms should exhibit variation in immunity that reflects the influence of their past (current condition) on the prospects of their future (reproductive potential). We measured two components of immunity (PHA response and bactericidal capacity of the blood) as well as basal corticosterone (CORT) in second-year (SY) and after-second-year (ASY) Red-winged Blackbirds during the breeding and non-breeding seasons to determine how age and sex influence investment in immunity. Mean PHA and CORT levels were lower in the non-breeding season for all age and sex classes but there were no other universal trends. The data indicate that the sexes and age classes have different strategies for resource allocation and/or experience a different set of physiological constraints from each other. In some cases the different strategies were not apparent as different mean values. Of particular note was that SY and ASY females did not differ in mean PHA response or bactericidal capacity during the breeding season, but SY females exhibited a significant decline in both measures of immunity over the course of the breeding season whereas ASY females exhibited no change (PHA) or a significant increase (bactericidal capacity) over the breeding season. Our data suggest that the birds’ levels of immune function reflect a complex interplay between current condition and reproductive potential, and that researchers examining immune function need to consider age and variation over time as important variables.