Spermatogenesis in the Siberian salamander, Salamandrella keyserlingii (Caudata: Hynobiidae)

Spermatogenic cycles of hynobiid salamanders are interesting for the study of male reproductive adaptations in amphibians living under different environmental conditions. In order to detect the main differences between spermatogenic cycles of hynobiids, we studied the spermatogenic cycle of Salamandrella keyserlingii from the suburbs of Tomsk (southeastern Western Siberia) and compared it with those in the literature of hynobiids from different regions of Asia. We histologically and histochemically examined the testes of males captured from April to September. In April, the testes of males entering breeding sites contained bundles of spermatozoa (Sz) and primary (Sg I) and secondary spermatogonia (Sg II). After spermiation and breeding, Sg II began to proliferate. Meiosis of spermatocytes occurred in late June through July. The spermiogenesis began in late July; spermatids and Sz appeared in August. In September, Sz, Sg I, and Sg II were found in testes, which was also when Sg II proliferated. There are two types of spermatogenic cycles in the studied salamanders. The first one includes one period of spermatogonial proliferation (SP) in the first half of the active season. The second type consists of two periods of SP, with one occurring at the beginning and the other at the end of the active season. To identify possible differences in hynobiid spermatogenic cycles, we tested the relation of the duration of active season (DAS), the duration of SP period in the first half of cycle (DSPP), and the number of SP periods per year (NSPPs), considering environmental (air) temperatures in these species' habitats. We could not find a direct relationship between NSPPs and air temperatures, but DAS and DSPP were correlated with temperature. We assume that two periods of SP can play the most apparent adaptive role in S. keyserlingii in a subarctic climate and in Batrachuperus tibetanus under mountain conditions.