Guarding your girl linked to sperm quality in humans

Men who perform "mate guarding" behaviours such as staying close to their wife or girlfriend at a party are likely to have poorer-quality sperm than men who do not, research suggests.

A UWA study surveyed 45 WA men in committed heterosexual relationships about their mate guarding actions and analysed their ejaculate samples.

It found men who performed fewer mate guarding behaviours had a greater concentration of sperm, a higher percentage of motile sperm and sperm that swam faster and less erratically than men who performed more.

Samantha Leivers, who conducted the UWA PhD research, says there is evidence mate guarding behaviour is linked to sperm quality in birds and fish but the study is the first to investigate the relationship in people.

She says mate guarding in humans is quite broad and can include anything from physically defending a partner to giving flowers, jewellery or an engagement ring.

"Some of the behaviours can be not leaving your partner's side at a party or you can give a guy the stink eye if he's looking at your girlfriend or you can actually physically attack another man if you think that he's at your girlfriend," Ms Leivers says.

"There's also subtle ways, so giving gifts signals to other men that 'this woman's in a relationship'.

"Even the more negative things that you think of, like moaning about your partner to your friends, because that makes her look like a less desirable mate to them."

Situational factors considered

Ms Leivers says it is unclear from the study whether sperm quality is plastic (dependent on situational factors) or fixed when it comes to mate guarding.

She says men who are unable to mate guard due to circumstances such as long distance relationships or a partner that does not allow mate guarding, may experience a plastic effect that improves his sperm quality.

"Once he's able to start mate guarding more, maybe the sperm quality would decrease.

"Another idea is that it's actually fixed, in that men who naturally have lower quality sperm basically increase their chances of paternity through the mate guarding.

"So if they have low quality sperm there is just this innate response that they have to increase their mate guarding behaviour."

Ms Leivers says the question is very difficult to answer in humans because it would be unethical to manipulate peoples' behaviour in relationships.

"My guess would probably be that it's plastic but we don't know," she says.