Abstract

Investigations were made into profiles of plasma androgens (combined testosterone and 5α-dihydrotestosterone) in green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles inhabiting waters off Queensland, Australia. First, we documented the occurrence of sex-based and ontogenetic changes in plasma androgen of immature green and hawksbill turtles occurring in wild populations. Specifically, androgen levels are increased in pubescent individuals and adults of both species and sexes. Second, we measured seasonal variation in plasma androgen profiles of adult male green and hawksbill turtles. Third, we compared plasma androgens of post-nesting green and hawksbill turtles. As for previous studies on captive green turtles, our data indicate that wild populations of green turtles also show a prenuptial spermatogenic pattern, in which plasma androgen levels rise and peak prior to migration and courtship. However, our data from male hawksbill turtles are in contrast to this pattern and provide some evidence to suggest that a delayed phase shift may occur in this population. Unlike male green turtles, male hawksbill turtles in this study all showed signs of physiological preparation for breeding.