AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 1 62-R66, Copyright © 1985 by American Physiological Society
Small male body size in garter snake depends on testes
D. Crews, M. A. Diamond, J. Whittier and R. Mason
In the red-sided garter snake (Thamnophis sirtalis parietalis) adult
females are larger than adult males; this difference is apparent within 3
wk of birth, a time coinciding with high circulating levels of androgens.
To study the ontogeny and regulation of this sexual dimorphism, male
neonates were either castrated, castrated and given Silastic capsules
containing testosterone or estradiol, or given a sham operation at 8, 9, or
10 wk of age. Female neonates were either given a Silastic capsule
containing testosterone or dihydrotestosterone or given a sham operation at
8, 9, 10, or 14 wk of age. The sex difference in body size and growth rate
in neonates was abolished by castration; the pattern of growth of castrated
males was similar to sham-operated females. Androgens in the amounts
administered failed to reverse the effects of castration, because castrated
male and female neonates receiving exogenous androgens grew at the same
rate as did sham-operated females. Males castrated as adults grow larger
than adult males given a sham operation, indicating the inhibitory role of
the testes on body size exists after sexual maturity. Treatment of adult
males with testosterone, however, prevented the increase in body size after
castration, suggesting that the mechanism regulating weight gain in the
garter snake depends on gonadal androgen.
