Influence of photoperiod on differentiation of male cells in Helix aspersa. An autoradiographic study.

Hibernating snails (Helix aspersa) were activated by placing them in environmental chambers under either long-day (LD 18:6) or short-day (LD 8:16) lighting conditions. One day after activation all the snails were injected with (3H-thymidine (5 microCi/g wet weight) in order to estimate the duration of spermatogenic phases under long and short-day cycles. Our histological and autoradiographic observations show that long-day cycles have a positive influence on the development of the male cell line, which becomes apparent from the third week of exposure. While in long-day snails labeled spermatozoa were identifiable 28 days after (3H)-thymidine injection, in short-day snails neither labeled spermatozoa nor spermatids were present in the gonads of animals killed as late as 39 days post-injection. These data strongly suggest that the photoperiod, besides acting on spermatogonial proliferation (Sokolove et al., 1983; Gomot and Griffond, 1987), has an important effect on the second meiotic division. In the course of spermatogenesis in Helix aspersa, the step from secondary spermatocyte to spermatid is probably the most sensitive to environmental factors.