Sperm storage in Crotalus durissus (Serpentes: Crotalinae): histological insights about the female reproductive tract of pit vipers

Abstract

The reproductive cycle of Crotalus durissus is markedly seasonal and synchronous between individuals. The start of vitellogenesis occurs at the end of the summer and coincides with copulation. However, given that the copulation is dissociated from ovulation, sperm storage is obligatory in females. In viperids, sperm storage in the female reproductive tract is reported to occur in two regions: (1) the posterior infundibulum, which presents sperm storage glands; and (2) the nonglandular uterus where sperm is stored in crypts by means of the uterine muscular twisting (UMT). The mechanisms that allow the survival of sperm in the female reproductive tract of snakes are still unknown. In this study, we investigated five regions of the reproductive tract of C. durissus, searching for the presence of spermatozoa and sperm storage structures in different oviductal portions. Additionally, we used histological techniques to verify the occurrence of hypertrophy of the infundibular and uterine glands during the processes of vitellogenesis, as well as histochemical techniques to investigate the nature of the secretion produced in the nonglandular uterus and posterior infundibulum. Storage sperm were observed in the nonglandular uterus and although the posterior infundibulum had storage receptacles, sperm were not observed in that region. Both sperm storage regions presented granules testing positive for acidic and neutral polysaccharides, in vitellogenic and previtellogenic females. This presence of guaranteeing conditions for sperm storage. Histochemical analysis revealed the possible storage capacity of sperm in the nonglandular uterus. In addition, the UMT was observed in all the females with storage sperm, which assures the maintenance of sperm in the nonglandular uterus until ovulation.