Reproductive Biology of the Massasauga (Sistrurus catenatus) from South-Central Illinois

This study was conducted at Carlyle Lake, Clinton County, Illinois. Brood size averaged eight and was not significantly correlated with maternal snout-vent length. Based on preserved snakes, females initiate vitellogenesis in the summer/fall. Vitellogenic follicles reach 20 mm in length by late September, overwinter at this size, and resume growth in the spring. Ovulation occurs later in the spring. Spermatogenesis begins in June and peaks in August and September. The diameter of the seminiferous tubules is less than 200 μm in May and reaches a diameter of 300 μm in late July to early September. The seasonal cycle of the sexual segment of the kidney parallels the changes in diameter of the testis. Sexual segment tubules are smallest in the early part of the activity season and peak in diameter and secretory activity from August through September. Mating and male-male combat occur primarily in the summer when the sexual segment of the kidney is hypertrophied. As in other species of snakes, the sexual segment of the kidney never regresses completely, indicating that testosterone levels are elevated throughout the year. The elevated plasma testosterone levels, which may be necessary for long term sperm storage in the vas deferens, may also account for the occurrence of courtship behavior in males in the spring.