WADA, H.*; HAHN, T.P.; BREUNER, C.W.; University of Texas at Austin; University of California, Davis; University of Texas at Austin: Ontogeny of the stress response: comparison of two subspecies of white-crowned sparrow nestlings

Elevation of corticosterone (CORT) in response to stress is known to increase survival in adults by redirecting behavior and physiology. However, the ontogeny of the stress response and the role of CORT in developing animals have been largely ignored. Detrimental effects of CORT on growth and immune function enhance the importance of regulation in its secretion among developing young. Moreover, environmental factors may play a key role in shaping the pattern and the regulation of stress response. We investigated the ontogeny of the stress response in two subspecies of white-crowned sparrow nestlings; Zonotrichia leucophrys oriantha and nuttalli which develop under different environmental and temporal constraints. Blood samples were collected at 0 (baseline) and/or 30 minutes (stress-induced) after capture and corticosteroid binding globulin (CBG) and serum CORT levels were measured to calculate both total and free levels of CORT. In addition, ACTH challenges were used to investigate the changes in capacity of the adrenal through development in nuttalli. Stress-induced total CORT levels increased with age in both subspecies. However nuttalli showed more robust increase significantly earlier than in oriantha. CBG capacity also increased with age and the pattern of change was similar in the two subspecies. Thus stress-induced free CORT levels increased with age with nuttalli exhibiting faster development of the stress response. This demonstrates that differential environmental factors may play an important role in shaping the ontogeny of the stress response in white-crowned sparrows.