Meeting Abstract
Glucocorticoid hormones provide a mechanism for individuals to rapidly adjust their physiology and behavior to meet the challenges of a variable environment. An individual’s baseline levels of glucocorticoids reflect shifts in life history stage and resource demands while mediating a suite of physiological and behavioral changes that include immune modulation and resource allocation. Thus, glucocorticoids could facilitate a response to parasites that is optimized for an individual’s specific challenges and life history stage. We used an observational field study and a controlled experiment to test the role of glucocorticoids in mediating the response to Haemosporidian parasites (including those that cause avian malaria) in red-winged blackbirds ( Agelaius phoeniceus ). We found that increased circulating glucocorticoids were associated with reduced costs of parasite infection but were unrelated to parasite burden in free ranging breeding male birds. We then manipulated glucocorticoid levels in male birds held in outdoor aviaries and measured individual changes in the costs of infection and parasite burden. To address the mechanisms underlying the effects of glucocorticoids on the costs of infection, we evaluated effects of the hormone on the inflammatory immune response and tissue repair. Our findings suggest a potentially adaptive role for glucocorticoids in shifting the response to parasites to align with an individual’s current physiological challenges.
