63.4 Saturday, Jan. 5 Dihydrotestosterone Reduces Growth in a Female-Larger Lizard JOHN-ALDER, H.*; POLLOCK, N.; PAZDZIOR, D.; FEIGIN, S.; Rutgers Univ., New Brunswick; Rutgers Univ., New Brunswick; Rutgers Univ., New Brunswick; Rutgers Univ., New Brunswick email@example.com
Sex differences in adult body size (sexual size dimorphism; SSD) are widespread, and both male- and female-larger SSD is observed even among closely related species. Earlier investigators focused largely on sex differences in the balance of selective forces on body size, but more recent workers have investigated proximate regulation of growth leading to SSD. A growing body of evidence in squamate reptiles has shown a correlation between patterns of SSD and effects of testosterone (T) on growth, wherein T stimulates growth in male-larger species and inhibits growth in female-larger species. These data have given rise to the bipotential growth regulation (BPGR) hypothesis to explain SSD in squamates and perhaps more broadly. However, mechanism(s) of BPGR, including possible conversions of T to estradiol and dihydrotestosterone (DHT), are conjectural. The present study tests whether growth inhibition by T in a female-larger lizard (Sceloporus undulatus; Eastern Fence Lizard) is an androgenic effect not involving aromatization of T to estradiol. Experiments were conducted on yearling males and females of S. undulatus. DHT was administered via implanted Silastic tubules in intact females and in intact and surgically castrated males. Body size was measured at regular intervals for six weeks. Compared to controls, growth rate was reduced by DHT in females and in males. Body condition, measured by regressing log mass on log snout-vent length, was unaffected by DHT, indicating that growth reduction was not caused by negative energy balance. Our results help to clarify the androgenic mechanism(s) of BPGR, wherein T inhibits growth in males of female-larger lizards.