Effects of testosterone on sexual behavior and morphology in adult female leopard geckos, Eublepharis macularius

The leopard gecko, Eublepharis macularius, is a species in which testostero ne (T) is the primary circulating sex hormone in adults of both sexes. Ther e are, however, sex differences in T physiology. Whereas males have prolong ed periods with high T levels, T levels cycle in accord with follicular dev elopment in females. Specifically, T concentration increases during vitello genesis, drops after ovulation, and then remains at previtellogenic levels until eggs are laid and the next follicular cycle begins. To determine the function of T in females, we manipulated both the level and the duration of T elevation using Silastic implants in intact, adult female leopard geckos . Females had low (similar to 1 ng/ml), medium (similar to 100 ng/ml), or h igh (similar to 200 ng/ml) T levels for either a short (8 days) or a long ( 35 days) duration. Behavior tests with males were conducted on days 1-5 in the short-duration group or on days 29-33 in the long-duration group. For b oth short- and long-duration groups, T treatment decreased attractivity in females with medium and high T levels compared to females with low T levels . In contrast, females with a medium T level were more receptive than femal es with a low T level in the short-duration group. Females in the long-dura tion group were unreceptive regardless of T level. Females treated for a lo ng duration also displayed more aggression toward and evoked more aggressio n from males than short duration females. Short-duration T treatment had no masculinizing effect on female morphology, whereas medium and high T level s for a long duration induced development of hemipenes. Overall, these resu lts suggest that T can both increase and decrease sexual behaviors in the f emale leopard gecko. (C) 1999 Academic Press.