Bad News for Bachelors

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Here's a real shocker: Living with a female can extend the reproductive life of a male mouse by as much as 20 percent, according to a new study from the University of Pennsylvania School of Veterinary Medicine.

The study's authors, writing in the journal Biology of Reproduction, believe the findings will have significant implications for male fertility in wildlife, livestock and even humans.

The females' impact on the environment of the spermatogonial stem cells probably occurs through the males' endocrine and nervous systems, the researchers suggest; "lonely" mice see their fertility reduced six months earlier than those who have female companionship.

"It appears that housing females with a male mouse delays the decline of reproductive processes at the cellular level by somehow affecting the cells surrounding the stem cells that produce spermatozoa in the testes," Ralph Brinster, professor of physiology and lead study author,was quoted in a press release announcing the findings. "Whether this female influence occurs in other species is not known."

For the study, male mice were housed with and without female companions for between 16 and 32 months; each male roomed with two different females every two months to determine whether it could impregnate the females. In addition to the observed six-month difference in reduced fertility rates, the study also indicated that once male fertility began to decline, the rate of decline was the same for male mice regardless of whether they lived with females.

While it has long been known that females can influence a variety of responses in male physiology and psychology, the study's findings could lead to revamped policy towards certain populations.

"If it turns out that this reproductive effect is mimicked in other species, for example, livestock animals that affect food production, then a 20 percent increase in male fertility could mean an extension of the male reproductive life span of years," Brinster said. "This finding may also have relevance for the protection of some large endangered species."

The research was supported by the National Institutes of Health and the Robert J. Kleberg Jr. and Helen C. Kleberg Foundation.