Synchrony of Male and Female Reproductive Parameters during the Biannual Reproductive Cycle of the Yellow Stingray, Urobatis jamaicensis (Myliobatiformes: Urotrygonidae)

Guy Harvey Oceanographic Center Facility

A definitive, biannual reproductive cycle with mature females capable of producing two broods annually was documented for the yellow stingray (Urobatis jamaicensis) in southeast Florida. Pregnant females were collected during all months throughout the year, but exhibited two discretely overlapping periods of reproduction. The first cycle extended from January to August and the second cycle from July to February. Male and female stingrays each demonstrated mutual synchrony with consistent bimodal patterns measured for nearly all reproductive parameters. Combining data from individuals on: follicle development, ovulation, embryonic growth, and parturition identified the periodicities of the repetitive female cycles with ovulation and parturition coinciding from January through April (Feb-Mar peak), and July through October (Aug-Sep peak). Sequential patterns of follicle development, with concurrent vitellogenesis and limited reproductive intervals, enabled females to breed immediately following or shortly after parturition of the previous cycle. Gestational periods overlapped during the transition between consecutive cycles (Jan-Feb & Jul-Aug). Thus these periods often displayed the simultaneous occurrence of either term stage females completing the previous cycle, or post-ovulatory females at the onset of the subsequent cycle. Gestation rates of ca. 5 months were estimated from the timing between peak ovulation, and observations of both postpartum females and free swimming neonates. Bimodal patterns of spermatogenesis and male sperm storage maintained appropriate levels of synchrony between male and female biannual cycles. Additional support of a biannual cycle was provided by significant differences between fecundity and lateralization of uterine function during each reproductive cycle.