Behavioral and physiological control of yolk synthesis and deposition in the female red-sided garter snake (Thamnophis sirtalis parietalis)

Ovarian recrudescence in female garter snakes, Thamnophis sirtalis parietalis, follows spring emergence from hibernation and mating. In the laboratory, courtship and mating stimuli significantly increased the proportion of female garter snakes becoming pregnant, although some noncourted nonmated controls also became pregnant. Females given artificial mating stimuli under anesthetic, without courtship stimuli, were no more likely than either noncourted, nonmated or anesthetized controls to become pregnant. Hormonal changes and yolk synthesis rapidly followed mating in both laboratory and field females; serum estradiol increased more than 10-fold in 2 days and serum calcium, a measure of yolk precursor lipoprotein (vitellogenin) concentration, increased more than two times in 10 days. Administration of exogenous estradiol stimulated yolk synthesis, but did not result in yolk deposition into ovarian follicles. However, administration of ovine follicle-stimulating hormone induced both hepatic yolk synthesis and yolk deposition. Our results are consistent with the hypotheses that (i) courtship and copulation are facilitatory to ovarian recrudescence but neither alone nor in combination is necessary nor sufficient, and (ii) in this species yolk synthesis and yolk deposition are separately regulated.