SEASONAL-CHANGES IN GONADAL ACTIVITY AND THE EFFECTS OF STRESS ON REPRODUCTIVE HORMONES IN THE COMMON SNAPPING TURTLE, CHELYDRA-SERPENTINA

The seasonal gonadal cycle (including gonadal histology, sex steroids, and gonadotropins) was studied in freshly captured common snapping tu rtles, Chelydra serpentina, from Wisconsin, and the effects of capture stress were evaluated. The ovarian and testicular cycles are shorter than those reported in other freshwater turtles; the cycles commence i n mid-May and terminate in early September, immediately after the comp letion of gonadal growth and maturation. In the female, testosterone ( T), 17 beta-estradiol (E-2), and progesterone (Pro) were highly correl ated with follicular growth and vitellogenesis. Ovulation in captivity and under natural conditions occurred after mid-May. In captivity, ov ulation was a rapid process (24-48 hr); as the follicles descended int o the uterine horns there was a significant increase in E-2 and Pro an d eggs were retained in the uterine horns for about 2 weeks before ovi position. In the male, T was significantly correlated with testicular growth and spermiation. Follicle-stimulating hormone (FSH) reached sig nificantly higher levels (P < 0.01) in males (8.99 +/- 0.38 ng/ml) tha n in females (2.66 +/- 0.22 ng/ml), but luteinizing hormone was undete ctable in both sexes. FSH was not correlated with the steroids in eith er sex. Sex steroids and FSH began to rise before spermiation and vite llogenesis and remained elevated until completion of gonadal growth an d maturation. Leydig cells, the main source of plasma androgen in this species, became active shortly after emergence from hibernation and r emained steroidogenically active for the rest of the cycle. Sertoli ce lls became active only after spermatogenesis was under way but also st ayed active for the rest of the summer. Courtship and mating behaviors were observed in spring, summer, and fall. The snapping turtle is str ictly aquatic with no basking behavior and limited behavioral thermore gulation so there is little daily fluctuation in body temperature. Env ironmental correlates indicate that the snapping turtle is temperature dependent: recrudesence occurs with a slight increase in water temper ature during spring and early summer, while a dramatic drop in gonadal activity accompanies a slight decrease in temperature in fall. Change s in temperature may underlie changes in gonadal activity in the face of relatively stable FSH. Male turtles subjected to captivity and peri odic blood sampling show a significant decline in T. The hormonal leve ls continued to decline whether the turtles are exposed to optimum or extreme temperatures. However, there is more rapid decline in T values in animals with regressed testes (June) than in those with well-devel oped testes (July). Male and female turtles kept in captivity at diffe rent phases of the cycle exhibit different patterns and degrees of res ponse to stress, possibly related to the hormonal levels and the condi tion of the gonads. (C) 1997 Academic Press.