Scientists reveal how females store sperm for decades

January 26, 2012 By Tamera Jones, PlanetEarth Online
Scientists reveal how females store sperm for decades
Sperm in search of the ovum.

( -- Scientists have discovered that all sorts of females – from birds to reptiles to insects – have a nifty trick to prolong the lifespan of sperm, letting them store it for weeks, months or even years on end.

They found that do this by lowering the metabolic rate of , so it can survive in their bodies almost indefinitely.

In one extreme example, biologists have shown that queen ants fertilise their eggs with sperm they've stored for up to 30 years. Normally, once it's outside the male's body, it doesn't survive for long.

The findings could explain why, in reproductive medicine, sperm samples aren't necessarily the best way to predict if someone can father children or not.

"Infertility tests on sperm are notoriously unreliable, and this could be one reason why," says Dr. Klaus Reinhardt from the University of Sheffield, who led the study, published in .

It seems that females lower sperm's metabolic rate and stop sperm generating excessive amounts of highly damaging, reactive oxygen molecules – called . Having a slower metabolism in turn means sperm age much more slowly than usual.

At the moment, Reinhardt and his colleagues have no idea how females manage this.

"All cells produce these molecules, but sperm tend to produce more, probably because they have such fast metabolisms. What's more, reactive oxygen molecules are thought to accelerate aging in all cells. So it follows that getting rid of free radicals might extend the lifespan of sperm," says Reinhardt.

The idea that free radicals contribute to aging isn't new. Nutritionists have long promoted the idea of eating foods like fruit and vegetables, because evidence suggests they contain antioxidants which mop up free radicals.

While some had suggested that females prevent sperm producing free radicals by lowering their metabolic rate, no-one had shown this, until now.

"Females could be manipulating sperm in such a way that they produce much fewer radicals in the first place," explains Reinhardt.

So Reinhardt and his colleague Anne-Cécile Ribou from the University of Perpignan in France decided to borrow a technique from the field of cancer research to investigate.

They used a technique called fluorescence-lifetime measurement to analyse sperm taken from the female crickets' reproductive tracts. The technique let them monitor both the metabolic rate of male crickets' sperm cells and how many oxidative free radicals they produce at the same time.

They found that the metabolic rate of sperm stored in the female Mediterranean field cricket for anything from an hour to 26 days went down by a massive 37 per cent compared with un-stored sperm. This tied in with the finding that a low metabolic rate corresponded with low free radical production.

But they also discovered that in sperm taken from the male the processes are entirely different: sperm that metabolise more quickly don't necessarily create more molecules.

"So in this case the current view in ageing research that a higher metabolism equals faster ageing doesn't hold," says Reinhardt.

Another thing the team noticed is that the metabolic rate in un-stored sperm doesn't predict its once it's stored in the female.

"This is pretty much why fertility predictions may not work so well. One reason that females don't let sperm keep going like hell once inside their reproductive tracts is probably that it is cheaper for them to shut down sperm than to support their energy requirements."

"This is something we'd like to investigate in the future," Reinhardt says.

Explore further: Crickets show path to chirpier sperm

More information: Anne-Cécile Ribou and Klaus Reinhardt, Reduced metabolic rate and oxygen radicals production in stored insect sperm, Proceedings of the Royal Society B, published 25 January 2012, doi:10.1098/rspb.2011.2422

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2 / 5 (1) Jan 26, 2012
The writer makes it sound like this lowering of the sperm metabolic rate was somehow involuntary, from the sperm's point of view. That can hardly be the case. A species should be perceived as one unit, and therefore actions and reactions between the sexes should not be considered a war.

It is just as much "in the interest of the male" to have sperm that tolerates storage, if one insists on this antagonistic approach.

Having understood this, it becomes clear that sperm has a mechanism to almost suspend its metabolism, and all it needs is to know when. Typically such messages are mediated by the presence of some molecule that the sperm otherwise don't encounter.

I'd suggest searching for candidates for this role.
not rated yet Jan 26, 2012
But from an evolutionary point of view the sexes often have very different strategies that increase fitness. It would only be in the interest of a male that has sperm that tolerate storage if that means his sperm is more successful at fertilizing eggs.

If that isn't the case, then coevolution of strategies that deactivate by females and ways to avoid that deactivation by males would be present. Sexual conflict is real either way.
not rated yet Jan 26, 2012
I thought Monica Lewinsky already figured this one out?

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