To store or mature spermatozoa? The primary role of the epididymis

Abstract

The function of the epididymis is considered in the context that it is necessary to transport spermatozoa for internal fertilization, but is also an adaptation involved in the competition between males to achieve paternity. Post-testicular sperm maturation and storage occur in lower vertebrates, such as the chondrichthyes, in which sperm storage is essential due to the slow rate of spermatogenesis. These roles persist in higher vertebrates, including mammals. However, they are less important in certain birds, in which the rate of sperm production by the testes is sufficient to supply enough spermatozoa to cope with the demands of a competitive mating system. There is no evidence for mammals, other than humans, that spermatozoa can achieve the capacity to fertilize an ovum without passing through some of the proximal epididymis. Storage of spermatozoa in the epididymis is probably not essential for a male to achieve conception in a protected mating system, but is very important in a competitive mating system. There is some variation between species in the magnitude of the epididymal storage region. This is related to the descent of the epididymides (and testes) into a scrotal sac in some species and/or the demands of the mating system in other species. The claims that humans are not dependent on post-testicular sperm maturation and storage need to be qualified, as they are based on studies of abnormal tracts and tests of fertility which are not rigorous. Nevertheless, the claims are of considerable clinical significance and may indicate that humans are less dependent on post-testicular sperm maturation and storage than other mammals. This may be an adaptation of the testes and epididymides to the scrotal conditions of modern man or a response to changing environmental factors.

Dynamic expression pattern and subcellular localization of the Rhox10 homeobox transcription factor during early germ cell development

“…5) suggests the possibility that RHOX10 has a function in the caput. For example, RHOX10 might promote sperm maturation, as this is known to occur in the caput (Cosentino & Cockett 1986, Jones 1999. We previously showed that another member of the Rhox gene cluster selectively expressed in the caput -Rhox5 -promotes the acquisition of sperm forward motility (Rao et al 2002.…”

Mammalian epididymal proteome

“…It is also essential that the epididymides accumulate and store sperm as, depending upon species, it takes 0.5 to 2 days for the testes to produce the number of sperm in a normal ejaculate, and in a competitive mating system 30 males may inseminate up to 50 females in a day (Jones, 1999;Jones et al, 2007). The efficacy of sperm storage in the epididymis is so high that fertile sperm can survive in an isolated epididymis for several days at 4°C (Guérin et al, 2003) The epididymis is a very long duct which receives testicular sperm via the efferent ducts.…”

Morphological Changes of the Epididymis and Description of the Excurrent Ducts of Phrynops geoffroanus (Testudines: Chelidae) During the Reproductive Cycle

“…Throughout the chelonians from temperate regions that reproduce seasonally, the spermatozoa produced during the summer are stored in the epididymides and are used in matings that occur throughout the year (Jones, 1999;Gist et al, 2000).…”