Meeting Abstract

9.9  Sunday, Jan. 4  Divergent Response of the Innate Immune System to Acute Stress in Male and Female Brown-headed Cowbirds (Molothrus ater) MERRILL, L.*; ROTHSTEIN, S.I.; O’LOGHLEN, A.; Univ. of California, Santa Barbara lmerrill@lifesci.ucsb.edu

Researchers have found substantial evidence linking stress and immunosuppression in numerous animals. There are few studies, however, documenting the duration and degree of stress response in wild animals as manifested by changes in innate immunity. In this talk we present data on the bacteria-killing ability of a captive but wild-caught group of male and female Brown-headed Cowbirds exposed to an acute stressor. We measured the bacteria-killing levels of the birds blood at different intervals to obtain a time series profile of the immune response post stressor. We conducted two experimental sessions for each sex. For the first male session, we stressed the birds by aggressively chasing them around their cages for 15 second. In the second male, and both female sessions we stressed the birds by catching them and collecting blood to obtain baseline bacteria-killing levels. Males and females exhibited opposite responses to the stressor; male bacteria-killing levels declined before recovering, while female levels increased before returning to baseline. In the first experiment, male bacteria-killing levels declined at least 15% at 90 minutes post stressor and had begun to recover at two hours. In the second experiment, male levels declined eight percent between 30 and 60 minutes post stressor, and had recovered to baseline at two hours. Female bacteria-killing peaked 90 minutes post stressor approximately 20% above baseline, and returned to baseline three hours post stressor. These results show a sex-specific difference in immune response to acute stress. In addition, they demonstrate the speed with which the innate immune system responds to an acute stressor, and subsequently the length of time it takes to return to baseline levels.