The XVIIIth (New) International Congress of Zoology

Le XVIIIème (Nouveau) Congrès International de Zoologie

In most mammalian species, mating is confined to a specific period in the estrous cycle when the female is receptive to males. Once deposited in the female reproductive tract, sperm must survive until ovulation. For some species, such as mice, which mate during the ovulatory period, this can be a matter of minutes, while in other species, such as bats, it can be a matter of months. However, the principal site of sperm storage in all nonprimates that have been investigated is the oviduct. Storage takes place in special crypts or within mucosal folds. In many eutherian mammals, sperm are held within mucosal folds near the uterotubal junction by binding to the epithelial surface. This binding has been demonstrated to involve carbohydrate recognition in the hamster, Mesocricetus auratus, the horse, Equus caballus, and the cow, Bos taurus. In these species, a lectin-like molecule on the surface of sperm binds to a specific carbohydrate moiety on the surface of the epithelium. This interaction somehow serves to maintain the fertility of sperm while they are being held. As the time of ovulation approaches, sperm lose binding affinity for the carbohydrate and are released. The loss is associated with a process known as capacitation; that is, attaining the capacity to undergo the acrosome reaction and fertilize the oocyte. In some marsupials and insectivores, sperm are stored in distinct oviductal crypts, but they do not bind to the epithelium. A storage site has not been identified in the human fallopian tube, but incubation of human sperm with tubal epithelium in vitro prolongs sperm survival.