Meeting Abstract

9.5  Sunday, Jan. 4  Sources of variation in the hypothalamic-pituitary-adrenal axis of urban and desert birds. FOKIDIS, H. Bobby*; DEVICHE, Pierre; Arizona State University; Arizona State University bfokidis@asu.edu

Glucocorticoids (GCs) are the end products of an endocrine system called the hypothalamic-pituitary-adrenal (HPA) axis, which is activated in all vertebrates in response to stressful stimuli. The secretion of GCs has been the subject of substantial research in free-living animals. This research has shown that average plasma GC levels often differ across populations of conspecific individuals, but we know little regarding how this difference arises. We measured plasma corticosterone (CORT), the primary avian GC, in adult male Curve-billed Thrashers, Toxostoma curvirostre, belonging to an urban and a desert population, 30 minutes after an injection of corticotropin-releasing factor (CRF), arginine vasotocin (AVT), or adrenocorticotropin hormone (ACTH). Administration of AVT or ACTH increased plasma CORT, and urban thrashers showed a greater acute response to these hormones than desert birds. In contrast, CRF treatment had no influence on plasma CORT in either population. Population differences in resistance to negative feedback of GC on the brain and pituitary gland were assessed by comparing plasma CORT before and 30 minutes after an injection of the synthetic GC dexamethasone (DEX). DEX administration decreased plasma CORT to the same extent in urban and desert thrashers. These data suggest that urban thrashers have a higher pituitary and adrenal gland sensitivity to AVT and ACTH, respectively, than desert birds. This difference in turn indicates an overall increase in HPA axis activity, possibly associated with repeated activation of this axis, in birds dealing with urban environment-associated stressors.