SIMON WESTENDORF, S.*; PALMER, B.D.: Seasonal pattern of plasma steroid levels and ovarian growth in the adult female slider turtle, Trachemys scripta scripta.

The female seasonal reproductive cycle was studied in a captive South Carolina population of slider turtles (Trachemys scripta scripta) over a period of one year. Plasma concentrations of estradiol-17BETA, progesterone and testosterone were measured during the cycle using radioimmunoassay. Ovaries were removed from randomly selected individuals throughout the year to monitor ovarian growth. While mean ovarian mass increased from mid-summer through the following spring, the increase was not statistically significant. Mean plasma levels of all three hormones were relatively low throughout the year when compared to other freshwater turtle species. Estradiol levels were lowest, followed by testosterone and progesterone levels respectively. Circulating estradiol and testosterone levels exhibited no apparent pattern over the reproductive cycle. However progesterone concentrations, although relatively low and static during most of the year, displayed a distinct peak, possibly representing a spike, around ovulation. The periovulatory release of high levels of progesterone along with the short life of corpora lutea in these turtles, suggests that preovulatory follicles, rather than corpora lutea, may be the primary source of progesterone in slider turtles.