Sperm Solidarity

In the fight for fertilization, rodent sperm band together.

By Amos Kenigsberg|Monday, April 23, 2007

If a lion-disembowels-antelope clip has ever made you shiver at nature’s harsh logic, just remember that you, too, are the product of a competition called survival of the gametes. But recent research led by Simone Immler of the University of Sheffield in England has turned up unexpected cooperation among some rodents’ sperm, which latch together via hook-shaped heads in hordes of up to 100 and barrel egg-ward together, like a knot of football players rumbling toward the end zone.

Wondering if the dynamics of conception might differ between promiscuous and monogamous rodents, Immler’s team looked at 37 mouse and rat species, comparing the size of the males’ testes with their body size. (In more promiscuous species, males have larger testes so they can produce more sperm and beat out rivals.) When the researchers looked at the gametes themselves, they found that the more promiscuous the species, the longer the hook, increasing the potential for teamwork among related sperm. It seems that as competition between males becomes more intense, it pays for sperm from the same male to band together. But just as on TV’s Survivor, teammates may help each other out early on, but there’s only one winner.

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