Reproductive Cycle of the American Alligator

The reproductive cycle of the American alligator, Alligatormississippiensis, was studied using blood and tissue samplesfrom wild alligators, and blood samples drawn from a captivebreeding stock at the Rockefeller Wildlife Refuge in Louisiana.Generally the cycle commences in March as air and water temperaturesincrease. By early April the seminiferous tubules are full ofactively dividing spermatocytes and maturing spermatids. Testismass is greatest at this time and plasma testosterone is ata peak (>50 ng/ml), but mature spermatozoa do not appearuntil late April and mid May when mating takes place. Plasmatestosterone levels decline rapidly in June after spermiation,and are low to nondetectable in July and August when the testesare fully regressed. A second small peak in testosterone occursin September without any obvious changes in testicular histology.In the female a similar temperature dependent initiation ofthe ovarian cycle occurs in late March. Plasma estradiol levelsreach a peak (>600 pg/ml) in mid April, and ovarian folliclesincrease from 5 mm to 45 mm in diameter at ovulation in May.Plasma testosterone is also high in preovulatory females (ca.1.5 ng/ml). Plasma progesterone shows a periovulatory surgeto levels as high as 16 ng/ml, but declines rapidly during the3 wk between ovulation and oviposition. During egg incubation(66 days) when the female remains close to the nest, ovariansteroids remain undetectable.