Pattern of plasma sex steroid hormone levels during reproductive cycles of male and female tropical lizard, Calotes versicolor.

Annual changes in gonadal activity and plasma sex steroid hormone levels in male and female Calotes versicolor [plasma testosterone (T) levels in males and 17 beta-estradiol (E(2)) and progesterone (P) levels in females] are described. In females both plasma E(2) (32.80 +/- 12.91 pg/ml) and P (1.72 +/- 0.79 ng/ml) levels are at their low levels during the postbreeding season when the gonads are regressed. With the onset of recruitment of vitellogenic follicles, E(2) levels begin to rise, reaching peak values (1306.00 +/- 407.01 pg/ml) when the follicles are preovulatory. During this time, plasma levels of P are low. Plasma E(2) levels decline (285.60 +/- 143.0 pg/ml) soon after ovulation, and circulating concentrations of P begin to rise, reaching peak value (19.24 +/- 10.03 ng/ml), during eggshell formation. In gravid females, at mid-gestation, the same pattern of E(2) secretion is found when a second set of follicles undergoes vitellogenesis. However, P levels remain low from mid-gestation (4.06 +/- 2.17 ng/ml) until oviposition. These findings suggest that high P levels are not needed for oviductal egg retention during late gestation and that low levels of P may facilitate growth of a new batch of vitellogenic follicles. In males, plasma levels of T are correlated with the spermatogenetic activity that accompanies breeding.