Meeting Abstract

38.10  Tuesday, Jan. 5  Changes in the innate immune systems of male and female brown-headed cowbirds in response to CORT: why do the sexes differ? 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; Univesity of California, Davis lmerrill@lifesci.ucsb.edu

There is substantial evidence indicating that stress causes a reduction in immune function in many animals. Potential causes for this change in immune activity range from a reallocation of shared resources to the avoidance of immunopathology. To gain a better understanding of the relationship between stress and immune function we have been examining the effects of acute stress on innate immunity in Brown-headed Cowbirds (Molothrus ater). Stress responses were initiated via capture and handling, and also via artificially elevated levels of the stress hormone corticosterone (CORT). CORT was injected into mealworms which were fed remotely to cowbirds so as avoid an associated stress event. Male cowbirds exhibited a significant decrease in immune function (bactericidal capacity of the plasma) following both handling and CORT manipulation, whereas female cowbirds exhibited no change in immune function following either manipulation. We will be examining levels of corticosteroid binding globulins (CBGs) to determine if the differences in changes in bactericidal capacity are related to variation in levels of CBGs. Female cowbirds may exhibit elevated levels of CBGs to mitigate the effects of a stress response in order to maintain reproductive function during the breeding season.