Seasonal variation in reproductive steroids of male and female yellow-blotched map turtles, Graptemys flavimaculata

From April to October of 1996 and 1997, we measured seasonal changes in pla sma testosterone (T) in male and plasma T and estradiol-17 beta (E-2) in fe male yellow-blotched map turtles, Graptemys flavimaculata, from the Pascago ula River, Mississippi. In 1996, plasma from females was analyzed for proge sterone. In 1997, ovaries of adult females were ultrasound imaged to determ ine stages of follicular development. Males exhibited peak T levels in Sept ember and October of both years, indicating fall gonadal activity. Males al so exhibited a low level spring peak in T during April. Female E-2 levels i ncreased significantly in May and June, the primary period of ovarian devel opment. Females with preovulatory follicles did not have significantly high er E-2 levels than females with medium- or small-sized follicles. When comp ared to other freshwater turtle species, peak levels of E-2 were low. Testo sterone levels did not follow a distinct yearly pattern in females. Progest erone levels were elevated in June when peak nesting was observed. Ultrasou nd and hormone data indicate that females lack ovarian development in the f all and produce on average only one clutch per year. (C) 2000 Academic Pres s.