Meeting Abstract

96.4  Wednesday, Jan. 7  Testosterone stimulates growth in a lizard (Anolis sagrei) with extreme male-biased sexual size dimorphism COX, Robert*; STENQUIST, Derek; CALSBEEK, Ryan; Dartmouth College; Dartmouth College; Dartmouth College robert.m.cox@dartmouth.edu

The brown anole (Anolis sagrei) exhibits extreme sexual size dimorphism (SSD) in which adult males exceed females by about 30% in snout-vent length and 140% in body mass. Recent studies show that the sex steroid testosterone can act as a bipotential regulator of SSD by stimulating growth in species with male-biased SSD and inhibiting growth in species with female-biased SSD. Thus, we predicted that testosterone should stimulate growth in A. sagrei. We raised A. sagrei lizards in captivity from hatching through adulthood to characterize the ontogeny of SSD and verify that sexual differences in growth give rise to SSD in captivity. Males and females did not differ in size at hatching, but males grew significantly faster than females throughout postnatal ontogeny to reach substantially greater adult sizes. We tested the hypothesis that testosterone stimulates growth using surgical castration and testosterone replacement in adult males. Castrated males receiving testosterone implants grew significantly faster in length and mass than castrated males receiving placebo implants. Growth rates of intact control males were intermediate. Our results support the hypothesis that testosterone acts as a bipotential regulator of sexual differences in growth that give rise to SSD.