Reproduction in the mexican leaf frog, Pachymedusa dacnicolor: II. The male

Abstract

The Mexican leaf frog, Pachymedusa dacnicolor, an inhabitant of the semiarid, subtropical Mexican lowlands, displays a well-defined seasonal testicular cycle. Testis weight seems to be a reliable index of the reproductive status of the animal and plasma levels of androgens (testosterone, T; 5α-dihydrotestosterone, DHT; androstenedione, A) correlate not only with testicular growth, but with callosity development, reproductive behavior, and breeding. During the fall and winter, testis weight reaches its minimum as do plasma concentrations of T, DHT, A, and estradiol-17β (E). Plasma levels of progesterone (P) are maintained at a very low level throughout the year. During the fall and winter, spermatogenesis is almost entirely absent and the callosities are white and smooth. No signs of reproductive behavior (calling and amplexus) are evident. Late spring marks the initiation of spermatogenesis, testis weight increase, darkening of callosities, and increase in plasma levels of androgens. The magnitude of callosity development and the onset of calling and amplectant behavior are correlated with a great rise in plasma androgen levels. Although plasma T concentrations were higher than plasma levels of DHT and A, this androgen failed to stimulate the development of callosities and calling behavior in successfully castrated males.