COX, R. M.*; SKELLY, S. L.; LEO, A.; JOHN-ALDER, H. B.; Rutgers University; Rutgers University; Rutgers University; Rutgers University: Testosterone Regulates Sexually Dimorphic Coloration in the Eastern Fence Lizard,

Adult male Eastern Fence Lizards (Sceloporus undulatus) possess blue and black ventral patches that function in sex recognition and intrasexual social signaling, but this ventral coloration is absent or greatly reduced in females and juvenile males. Adult males also exhibit a relatively uniform, reddish brown dorsal coloration, while females and juvenile males are cryptically colored, with two rows of dark brown or black chevrons set against a background of gray and brown. We hypothesized that these sexual dimorphisms in ventral and dorsal coloration, which develop at the onset of sexual maturation, are regulated by the sex steroid testosterone. We experimentally tested this hypothesis by (1) removing the primary source of circulating testosterone in juvenile males via surgical castration, (2) restoring testosterone in castrated males with tonic-release implants, and (3) implanting intact juvenile females with exogenous testosterone. As predicted by our hypothesis, the development of blue and black ventral coloration was (1) inhibited by castration in juvenile males, (2) restored by exogenous testosterone following castration in juvenile males, and (3) promoted by exogenous testosterone in juvenile females. The expression of male-specific dorsal coloration was also (1) inhibited by castration, and (2) restored by exogenous testosterone following castration in juvenile males. Our results are consistent with an established literature supporting the critical role of androgens in the mediation of sexually dimorphic coloration among phrynosomatid lizards. Supported by NSF IBN-0135167.