Reproduction in the Mexican leaf frog, Pachymedusa dacnicolor. III. The female.

The female of the Mexican leaf frog, Pachymedusa dacnicolor, displays a marked annual ovarian cycle. This consists of a long period of vitellogenic stasis, starting in early fall, soon after the breeding season, and ending in early spring. Oogonial proliferation continues throughout the year and new previtellogenic follicles are formed continuously. During the period of vitellogenesis, from spring to early summer, early, advanced, and postvitellogenic follicles are all found together, a situation that continues through the breeding season. This is correlated with the fact that a breeding female can lay three or more clutches per season. Breeding can begin as early as June and end as late as early September, with peak spawning activity taking place during July and August. An examination of the ovarian hormone secretion pattern in P. dacnicolor during the year revealed that plasma levels of testosterone and estradiol correlated with ovarian growth and attained highest levels in amplectant and ovulating females. Both hormones showed quite similar plasma levels and patterns of change during the annual reproductive cycle. Lowest plasma levels of testosterone and estradiol were found during fall and winter, in females possessing exclusively previtellogenic ovarian follicles. Plasma progesterone levels were maintained at a very low level throughout the year, except for the ovulatory surge, when amplectant and ovulating females may show a three- to sixfold increase. Plasma androstenedione showed a low peak during this phase of the reproductive cycle. Plasma levels of 5 alpha-dihydrotestosterone were 13 to 30 times lower than plasma testosterone levels. The potential roles of these gonadal steroids in controlling ovarian activity and reproduction are discussed briefly.