Seasonal variation in the oviduct of female Agkistrodon piscivorus (Reptilia:Squamata): an ultrastructural investigation.

The annual oviductal cycle of the Cottonmouth, Agkistrodon piscivorus, is described using electron microscopy. This is only the second such study on a snake and the first on a viperid species. Specimens were collected in reproductive and nonreproductive condition throughout the year and five ultrastructurally unique regions were recognized: the anterior infundibulum, posterior infundibulum, glandular uterus, nonglandular uterus, and vagina. Except for the anterior infundibulum and vagina, which exhibit no seasonal variation in ultrastructure, the oviduct becomes highly secretory at the start of vitellogenesis. This includes the entire luminal border of the uterus, the tubular glands of the glandular uterus, and the luminal border and sperm storage tubules of the posterior infundibulum. The secretory materials produced in the oviduct vary among regions of the oviduct, and also can vary among time periods in the same region of the oviduct. Variation is especially evident in the sperm storage tubules. Secretory activity in the sperm storage tubules ceases after ovulation, but the tubular glands of the glandular uterus remain secretory until parturition, at which time secretory activity in the varying sections of the oviduct decreases dramatically. After parturition, the oviduct remains in a dormant state until the next reproductive season. The seasonal variation in oviducal morphology mirrors the temperate primitive reproductive cycle known for some pitvipers. Uterine glands of A. piscivorous are more similar in secretory activity to those of an oviparous lizard than a viviparous colubrid snake, suggesting variation in uterine gland morphology between snakes of different families.