Friday, January 23, 2009

Cohabiting with females boosts male fertility

ResearchBlogging.orgHow many times have you heard a guy say "Women - can't live with them, can't live without them." Well, they just might be onto something. At least kind of. You see, living with a woman might just make you fertile longer. New research published in Biology of Reproduction has found that male mice stay reproductively active longer if they live with a female mouse than if they live alone.

Frisky MiceThe study, from the University of Pennsylvania School of Veterinary Medicine, sought to see whether living with a female mouse had any affect on a male mouse's fertility as he aged. To do this, male mice were either housed with a female mouse continuously or isolated, given access to a virgin female only at given time intervals to prove fertility (sounds terrible to you guys, I'm sure). They also looked into factors of fertility like testes size and abnormal spermatogenesis at each time point.

They found that male mice which were housed with females were fertile a whopping 20% longer than the isolated males. Also, histological abnormal spermatogenesis appeared earlier in the isolated males, giving a possible mechanism to their sooner decrease in fertility. Interestingly enough, once a mouse started to decline in fertility, the rate at which he became infertile was the same between the two treatments, suggesting that once whatever processes by which a mouse loses fertility begin, they have a set time course.

What does this mean for us? If you want to put off having kids, perhaps having a girlfriend or wife live with you throughout your 20s and 30s will let you have kids later on. Or, conversely, if you live single and alone through those years, you might have a bit more trouble impregnating someone when you're older. It also may explain why males, who some might argue evolutionarily have an advantage by staying single and ready to mingle, form long-term bonds with females. It's possible that the added reproductive benefits of living with the same woman outweigh the costs - while sleeping with different ones and staying a bachelor gets you a few more kids while you're young, the added years of fertility give you more. Albeit that's a bit of a reach (and would require a lot more support), it's possible.

Now, the astute reader would point out at this juncture that the research was in mice, not humans. True, true. But there is the possibility, at least, that this effect could be true for other mammals, including us. Perhaps the most useful application if this phenomena is in other species, however, won't be in our own mating strategies but in the livestock and other breeding industries. Housing a prize stud horse with a nice female might give him a longer reproductive lifespan, meaning a lot more cha-ching for his owner. Or keeping endangered zoo animals with opposite-sexed partners might give struggling population breeding programs an extra boost.

In any case, this new finding might just open up some interesting new studies on the effects of cohabitation on reproduction, and perhaps what pathways this might occur by. And as always, if it's about sex, I'll probably be interested in their findings. I just can't seem to pull myself away from all this reproductive biology. I don't have my mind in the gutter - I swear.

J. A. Schmidt, J. M. Oatley, R. L. Brinster (2009). Female Mice Delay Reproductive Aging in Males Biology of Reproduction DOI: 10.1095/biolreprod.108.073619


Anonymous said...

Did they somehow control for the affect that ejaculating might have on fertility? Or did the isolated mice get it on as much?

Christie Lynn said...

I don't know if they somehow prevented the other mice from trying to mate while living together, so it's possible the cohabiting males ejaculated more, in general. Both were given two nice virgins to try and impregnate for a few weeks at each time point, so they did get to get some... Good question!

Anonymous said...

Studies have shown that married men are happier. Maybe the chemical effects of happy cohabitation also influence fertility.

Anonymous said...

The fact that a person is married doesnt mean that the person is happy. However, I agree that chemical effects of happiness derived from a happy cohabitation with satisfying sexual life may affect male fertility, I think, also female though, if the satisfaction is mutual and they are both hetero oriented.

Anonymous said...

I wonder if this could be related to some sort of kin altruism effect? I.e., mice that have difficulty attracting mates are better off using their resources to assist siblings?

Margaret said...

It makes sense that an isolated male would produce less sperm than one with an opportunity to mate regularly. Although spermatogenesis requires far less energy than the production of ova, it nevertheless does have a cost to the individual.

Christopher said...

The odd thing is that, in high population density areas, this means males would be more fertile, which would presumably result in more offspring. It seems like it should be the other way around. Admittedly in big cities in the U.S. it seems like people are more likely to live alone, but that's not true in other parts of the world.