Sperm storage in the viviparous lizard Sceloporus bicanthalis (Squamata: Phrynosomatidae), a species with continuous spermatogenesis

Sceloporus bicanthalis inhabits the Nevado de Toluca, Mexico, and the males exhibit continuous spermatogenesis with mature sperm available year round. Females were collected monthly to evaluate the morphology of the oviducts and the presence of sperm storage. Histological examination revealed that the oviductal structure in this lizard is similar to that described for other lacertilian species: anterior infundibulum, glandular uterus, and a posterior non-glandular uterus. The oviduct wall consists of a superficial visceral pleuroperitoneum, a middle layer of smooth muscle with outer longitudinal and inner circular fibers, and a deep mucosa or lamina propria deeply lined by an epithelium containing ciliated and non-ciliated secretory cells. Spermatozoa are stored at the base of the mucosal folds, in crypts and in sperm storage tubules at the transition between the glandular uterus and non-glandular uterus, as well as in the anterior non-glandular uterus of previtellogenic, vitellogenic, pregnant, and postpartum females. The sperm in the oviductal cavity or in retention sites is in contact with secretory products derived from non-ciliated epithelial cells. Spermatozoa usually assume an orderly distribution with their heads aligned and oriented toward the base of the folds or crypts. This study shows that females of S. bicanthalis exhibit prolonged sperm storage that corresponds with the continuous reproductive strategy employed by males.