Annual cycles of steroid hormone production, gonad development, and reproductive behavior in the Atlantic stingray

The mating season of the Atlantic stingray (Dasyatis sabina), which begins in August and continues through April, is the longest documented for any el asmobranch fish. Despite :this protracted mating period, female stingrays o vulate synchronously at the end of the mating season and there is no eviden ce for sperm storage by females. Thus, the proximate causal factors and ult imate function of this extended preovulatory mating are unknown. Annual cyc les of the gonadal steroids testosterone (T), dihydrotestosterone (DHT), 17 beta-estradiol (E-2), and progesterone (P-4) were measured for 26 months i n a wild estuarine population of Atlantic stingrays to test for association s with their reproductive biology, gametogenesis, and sexual behavior. Seru m androgen levels in males showed four phases within an annual cycle: (1) a ndrogen suppression between reproductive seasons (April-July), (2) primary androgen increase during the onset of spermatocyte development (August-Octo ber), (3) androgen decrease following maximum testis growth and spermatocyt e development (November-December), and (4) secondary androgen increase duri ng the peak of sperm maturation (January-March). Increases in male E-2 and P-4 were correlated with spermatocyte/spermatocyst formation, maximum testi s weight, and the primary (but not secondary) androgen surge. We propose th at the production of male androgens across the full seven-month preovulator y:mating period promotes their aggressive reproductive behavior and drives the protracted mating season of this species. In females, serum T and DHT s howed relatively brief increases near ovulation, whereas E-2 and P-4 showed brief increases near both ovulation and parturition. The increase in femal e androgens near ovulation may increase female aggression when they are imp regnable by courting males and enhance their choice of mates. This estuary sample population shows higher absolute steroid levels and distinct differe nces in temporal cycles compared to another Florida fresh water lake popula tion, but the cause and significance of these differences are unknown. Expe riments are needed to confirm that the aggressive and protracted mating beh avior is the result of prolonged male androgen production and to determine whether the sustained preovulatory mating serves some function related to f emale reproduction. (C) 2000 Academic Press.