Plasma steroids associated with seasonal reproductive changes in a multiclutched freshwater turtle, Sternotherus odoratus

Abstract

The annual reproductive cycle of the stinkpot turtle, Sternotherus odoratus, is described and correlated with plasma changes of testosterone in males, and estrogen, progesterone, and testosterone in females. Maximum plasma concentrations of testosterone in males were temporally associated with spermiogenesis and spermiation during fall. In winter, plasma testosterone levels declined and remained low until the renewal of spermiogenesis in summer. Females were observed to produce more than one clutch annually. After the oviposition of the last clutch of eggs, there was a brief period of ovarian inactivity, followed by vitellogenesis during fall. Females overwintered with preovulatory-size follicles, which were ovulated as the first clutch of eggs in spring. The three sex steroids underwent marked changes associated with the annual ovarian cycle. Testosterone concentrations increased during the periovulatory period of the first clutch, but during vitellogenesis, ovulation, and oviposition of the second and third clutches, plasma levels remained low. A small increase in testosterone level was associated with fall vitellogenesis. High estrogen titers were associated with the vitellogenic periods during fall and spring-early summer. Progesterone concentrations increased markedly during the periovulatory period and declined as shelling of the eggs progressed in the oviducts. A small increase in progesterone levels was observed during fall. These data are discussed with regard to the possible role of sex steroids in a multiclutched freshwater turtle.