Meeting Abstract

P2.146  Wednesday, Jan. 5  Effects of breeding season, testosterone and ACTH on the corticosterone response of free-living male fence lizards (Sceloporus undulatus) KLUKOWSKI, M.; Middle Tennessee State Univ., Murfreesboro mklukows@mtsu.edu

A relatively weak adrenocortical stress response during the breeding season has been reported for several vertebrate species, but the underlying physiological mechanism has received little attention in reptiles. Possible mechanisms include changes in the adrenal gland that influence its sensitivity to adrenocorticotropin hormone (ACTH) or upstream changes in the perception of stressors, the hypothalamus, or the anterior pituitary. Here I tested whether adult male Eastern Fence Lizards, Sceloporus undulatus, have a weakened corticosterone response to capture and 4 hours of confinement in the breeding season relative to the nonbreeding season. Plasma corticosterone levels in response to confinement were significantly lower in the breeding than the nonbreeding season. Second I tested for an effect of testosterone on the stress response by experimentally elevating plasma testosterone levels via silastic implants in free-living males during the nonbreeding season. Testosterone-treated male lizards had significantly lower levels of plasma corticosterone after one hour of confinement than sham-implanted males. Third I tested the capacity of the adrenal glands to secrete corticosterone during the breeding season by challenging males with ACTH injections. Males responded robustly to ACTH in the breeding season even though corticosterone responses to capture and confinement in saline-injected controls were weak. Taken as a whole, these results suggest that seasonal modulation of the adrenocortical stress response occurs upstream of the adrenal gland, as has been shown in some arctic-breeding avian species, and likely involves seasonal changes in testosterone levels.