26th Annual Meeting and Symposium of the
Desert Tortoise Council, March 16-18, 2001
Abstracts

Stress, Corticosterone and Testosterone in Male Desert Tortoises

Valentine A. Lance¹ and David C. Rostal^2
1Center for Reproduction of Endangered Species, P.O. Box 120551, San Diego, CA 92112
²Department of Biology, Georgia Southern University, Statesboro, GA 30460

Stress in male lizards, snakes and alligators results in an immediate rise in plasma corticosterone, and a rapid decrease in plasma testosterone. The elevated corticosterone is believed to inhibit the secretion of gonadotropin and thus shut down gonadal secretion of steroids. In male turtles and tortoises, however, there is a paradoxical rise in testosterone in response to stress. Corticosterone does increase as in other reptiles, but no decrease in testosterone is seen until about 24 hours after the onset of stress when corticosterone has also returned to pre-stress levels. In unstressed adult male tortoises, plasma corticosterone and testosterone show an identical seasonal pattern: when testosterone declines in mid summer, corticosterone declines. Regression analysis of the seasonal data for the two steroids gave a value of p<0.001. To test this relationship between the two hormones we injected adult male tortoises with ACTH (adrenocorticotropic hormone) and measured testosterone and corticosterone. Again both steroids increased in response to the ACTH injection. The reason for this linkage of corticosterone and testosterone secretion is not known, but the close anatomical relationship of the two tissues may play a role. Possible reasons for this unusual phenomenon will be discussed.