| Immature loggerhead, Caretta caretta, green, Chelonia mydas, and hawksbill, Eretmochelys imbricata, sea turtles had relatively low serum concentrations of testosterone (T), estradiol-17$beta$ (E$sb2$), and progesterone (Pro) during the prolonged maturation period in (possibly 50 years or more). However, immature males had significantly higher serum T than immature females and serum T increased significantly during "puberty" in male C. mydas. The results also suggest that T stimulates tail elongation, a secondary sexual characteristic, in males.;Serum T concentrations were used to predict the sex of 218 immature C. caretta captured near Hutchinson Island, FL. The sex ratio (2.1 female: 1.0 male) was significantly different from a 1:1 ratio predicted by sex allocation theory.;Adult male C. caretta possessed a prenuptial spermatogenic pattern that was positively correlated with increased serum T. Serum T remained high through migration and mating seasons suggesting that T could affect those behaviors. In contrast to adult females, adult male C. caretta may be reproductively active every year.;Adult female C. caretta also possessed a prenuptial pattern of gonadal recrudescence coincident with gonadal steroid production. Females exhibited a significant elevation in serum E$sb2$ approximately 4-6 weeks prior to migration indicating increased vitellogenesis. Serum T increased immediately prior to migration, suggesting that T could affect migratory and/or mating behaviors. Caretta caretta have relatively high serum T, E$sb2$, and Pro during nesting if there is to be a subsequent ovulation, otherwise the concentrations of all three steroids are low. In female C. caretta and C. mydas, serum T was high at the time of nesting and then decreased during the periovulatory period when serum follicle-stimulating hormone (FSH), luteinizing hormone (LH) and Pro increases significantly, suggesting that FSH, LH and Pro may stimulate ovulation, whereas T is a likely candidate for mediating the hormonal surges associated with ovulation.;The prenuptial gonadal cycles of C. caretta with temporally associated gonadal steroid production and reproductive behaviors indicate that marine adaptation may have facilitated the retention of a primitive reproductive cycle in sea turtles. Therefore, the actions suggested for gonadal steroids in sea turtles (including the classical roles in gametogenesis, ovulation, and mating, as well as a role in migration) may represent primitive functions for these hormones in reptiles. |
