Mechanisms of Sperm Storage in the Female Reproductive Tract: an Interspecies Comparison

Abstract

Contents Once semen has been collected for artificial insemination, it is diluted into extenders designed to prevent its deterioration over the period prior to insemination. If the semen is not frozen, the extenders provide protection for a period of a few hours to a few days, depending on species. Despite the efforts of biotechnologists to increase the duration of storage without compromising fertility, there has been relatively little progress for many years. However, comparative studies in diverse species have revealed that long‐term sperm storage (up to months and years) within the female reproductive tract is relatively commonplace in reptiles, fishes, birds and amphibians. Even among mammals, some species of bat have evolved mechanisms for storing spermatozoa for several months in the uterus or oviduct so that they can mate in the autumn but postpone fertilization until the spring. We currently know little about the mechanisms that support such long‐term sperm storage, mainly because evidence from such species is either absent or fragmentary. Nevertheless, parallels between mammalian and other systems, where spermatozoa are sequestered in sperm storage tubules, suggest that the enclosure of spermatozoa within pockets of epithelial cells may be sufficient to achieve long‐term sperm storage. In addition, recent evidence from sperm‐storing bats has suggested an alternative, or additional, hypothesis that the modulation of apoptosis within epithelial cells is important in controlling sperm survival. Despite a lack of direct experimental evidence from a wide variety of species, I propose that there is now enough evidence to warrant investigation of these hypotheses.

The Australian saltwater crocodile (Crocodylus porosus) provides evidence that the capacitation of spermatozoa may extend beyond the mammalian lineage

“…This strategy contrasts with other species in which direct contact between the spermatozoa and oviductal epithelium suppresses sperm function, and hence facilitates their longterm storage [49]. It has thus been suggested that sperm longevity in the female alligator may be a property of the male gamete [45].…”

Combined albumin and bicarbonate induces head-to-head sperm agglutination which physically prevents equine sperm–oviduct binding

“…Sperm storage after mating is a female reproductive tract phenomenon that has been observed in various animals with the presumed aim to preserving sperm fertilizing capacity in species in which mating and ovulation are poorly synchronized (Holt 2011). In the mare (Bader 1982, Scott et al 2000 and many other mammals (rabbit (Harper 1973), pig (Hunter 1981), sheep (Hunter & Nichol 1983), mouse (Suarez 1987), cattle (Hunter & Wilmut 1984) and hamster (Yanagimachi & Chang 1963)), an oviductal sperm reservoir is established at the uterotubal junction and the caudal part of the oviductal isthmus.…”

Beyond lifetime reproductive success: the posthumous reproductive dynamics of male Trinidadian guppies

“…Many organisms have been shown to store sperm inside the female reproductive tract [1]. Some examples include social insects [2], crabs [3], salamanders [4], turtles [5], lizards [6,7], bats [8] and fish [9,10].…”