Male reproductive cycle of the Siberian salamander Salamandrella keyserlingii (Caudata: Hynobiidae) in coastal tundra of the Sea of Okhotsk

The adaptations which allowed the Siberian salamander (Salamandrella keyserlingii Dybowski, 1870) to form its exceptionally large, polyzonal range (forest-steppe, forests, and southern tundras of Siberia and part of European Russia) remain insufficiently studied. We checked the hypothesis that S. keyserlingii was able to colonize the northern territories, characterized by a short and cold summer and therefore unsuitable for other amphibians, due to multiyear maturation of its spermatozoa and eggs which was described in the southern part of Western Siberia. For this purpose, the male reproductive cycle of S. keyserlingii was studied during the entire 4-month active season in the Sea of Okhotsk coastal tundras. The complete development of gametes there took only 3 months: proliferation of spermatogonia started already in the spawning pond soon after spermiation in May and ended by the time the males left the water; spermatocytes were formed at the end of June, and spermatozoa, by the second half of August. Spermatogenesis occurred synchronously in all the maturing lobules along the entire length of the testis. Mature spermatozoa were stored in the testes until spring when external fertilization took place in the pond. Morphological and histological changes in the testes and vasa deferentia, the mode of fertilization, and annual reproduction of S. keyserlingii were similar to those of other studied species of the family. Our data disprove the previous conclusion about multiyear spermatogenesis of S. keyserlingii, which, therefore, cannot be considered among the possible adaptations which facilitated colonization of the northern territories by this species.