The Reproductive Cycle of the Female American Alligator (Alligator mississippiensis)

Abstract

We examined ovarian and oviducal gross morphology and collected blood samples from wild female alligators in central Florida during most of the year. Females with vitellogenic follicles were observed throughout the year, although ovaries containing follicles larger than 15 mm were seen only during the spring and early summer (March–June). We detected a poor relationship between female body size and the number of vitellogenic follicles whereas body size was significantly correlated with clutch size. Plasma samples were analyzed for (1) estradiol-17β (E2), testosterone (T), and corticosterone by specific radioimmunoassays; (2) vitellogenin by one-dimensional sodium dodecyl sulfate–polyacrylamide gel electrophoresis; and (3) total protein, phosphorus, and calcium by spectrophotometric assays. Reproductively active females showed elevated plasma concentrations of E2during the fall (September–November) and spring (March–May) whereas non-reproductively active females exhibited basal levels with no apparent peaks. Vitellogenin was detected in the plasma during the same months that plasma E2concentrations were elevated. Elevated plasma vitellogenin and E2were not correlated with plasma total protein but were correlated with plasma calcium concentration. During late vitellogenesis, plasma T concentrations were elevated in reproductively active females coincident with a period of intense courtship and mating. Corticosterone plasma concentrations exhibit no significant monthly variation, nor apparent changes during various stages of reproductive activity although plasma concentrations were elevated during late gravidity. Our data suggest that female reproductive activity begins in the fall with an increase in plasma E2concentration in September or October and vitellogenesis in October. Ovarian activity slows during winter and reactivates with the onset of spring.