Variation in the Male Reproductive Cycle in a Population of Stinkpot Turtles, Sternotherus odoratus, from Virginia

Abstract

Annual variation in the testicular cycle of a population of stinkpot turtles, Sternotherus odoratus, from Virginia was found to occur in late stages of spermatogenesis but not in initiation of the cellular cycle or in the testis weight cycle. Seasonal variation in testis weight was generally concordant with variation in the spermatogenic cycle and followed the typical postnuptial pattern in which testicular growth and recrudescence begins in late spring, followed by peak weights and spermiogenesis in August, and regression in fall and winter. Minimum testis weights and onset of spermatogenesis were in May. The variables seminiferous tubule diameter, carapace length, and month accounted for 89.3% of the variation in testis weight; year accounted for 0.1%. Males in this population matured at the end of their second year at a minimum carapace length of 51 mm. Geographic variation in timing of spermatogenic events is discussed with reference to populations in Alabama and Michigan. Water temperature is the probable cue for initiation of spermatogenesis in stinkpots, and the variation in occurrence of later stages may be due to individual movement in the water column. Comparisons are made with the testicular cycle of a syntopic population of painted turtles, Chrysemys picta, studied concurrently.