Seasonal variation of the oviduct of the American alligator, Alligator mississippiensis (Reptilia: Crocodylia).

The annual oviductal cycle of the American alligator, Alligator mississippiensis, is described using light and electron microscopy. Previous work done by Palmer and Guillette ([1992] Biol Reprod 46:39-47) shed some light on the reproductive morphology of the female alligator oviduct; however, their study was limited and did not report details relating to variation across the reproductive season. We recognize six variable regions of the oviduct: infundibulum, tube, isthmus, anterior uterus, posterior uterus, and vagina. Each area shows variation, to some degree, in the histochemistry and ultrastructure of oviductal secretions. Peak secretory activity occurs during the months of May and June, with the greatest variation occurring in the tube and anterior uterus. During the month of May, high densities of neutral carbohydrates and proteins are found within the tubal and anterior uterine glands. The epithelium of the entire oviduct secretes neutral carbohydrates throughout the year, but many regions lack protein secretions, and the posterior uterine glands show little secretory activity of any type throughout the year. After oviposition, secretory activity decreases drastically, andthe oviduct resembles that of the premating season. This study also provides evidence to support the homology between alligator and bird oviducts. Sperm were observed in glands at the tubal-isthmus and utero-vaginal junctions in preovulatory, postovulatory and postovipository females.