Plasma androgen levels, spermatogenesis, and secondary sexual characteristics in two species of plethodontid salamanders with dissociated reproductive patterns.

In the summer of 1991 (late May to early September), I measured seasonal levels of plasma androgens in two species of plethodontid salamanders to assess the temporal relationship of elevated plasma androgen levels with spermatogenic events and with sexual behavior. In both species, spermatogenesis occurs in the spring and summer. In one species, Plethodon jordani, mating occurs in the fall. In the other species, Desmognathus ochrophaeus, the mating season is prolonged, occurring both in the fall and in the spring. In P. jordani, plasma testosterone (T) levels were lowest in June and highest in late August, such that elevated plasma T levels coincided with the development of secondary sexual characteristics and the time when mating behavior occurs. Plasma dihydrotestosterone (DHT) levels for P. jordani were lowest in June and rose significantly in mid July when spermiation began. In D. ochrophaeus, plasma T and DHT levels were lowest during June and July and highest in late August. Elevated T and DHT levels coincided with spermiation and with the period when mating behavior occurs. Data for these two salamander species indicate that maximally elevated plasma androgens were temporally dissociated from the peak of spermatogenesis; maximal androgen levels were more closely associated with spermiation and the development of secondary sexual characteristics.