Meeting Abstract
Corticosterone binding globulin (CBG) is the major transport protein for both corticosterone and testosterone steroids in birds and is primarily produced in the liver. Binding assays for CBG along with immunoassays for corticosterone, the stress hormone, indicate that both analytes can vary by life history stage and often peak during breeding. Additionally, harsh conditions are known to stimulate the hypothalamic-pituitary-adrenal (HPA) stress axis. We investigated how life history stage and environmental conditions influenced hepatic CBG mRNA expression in migratory and non-migratory subspecies of White-crowned sparrow (Zonotrichia leucophrys). We predicted that harsh conditions would promote CBG expression to aid steroid transport in the blood stream. Birds were sampled during breeding, molt and wintering life history stages. CBG was upregulated in male migrant sparrows compared to non-migratory residents during the breeding stage only. Migrants exhibited peak CBG expression during breeding while no other seasonal differences were detected for either subspecies regardless of sex. Our results suggest that CBG expression is affected by seasonal stage in migratory White-crowned sparrows only, possibly due to harsher environmental conditions experienced at breeding sites.
