Thaindian News

Washington, Jan 25 (IANS) Some mouse sperm can discriminate between its brethren and competing sperm from other males, clustering with its closest kin to swim faster in the race to the egg.
But this sort of cooperation appears to be present only in certain promiscuous species, where it affords an individual’s sperm a competitive edge over that of other males.

“The race among sperm toward the egg is fierce, but never more so than when sperm of different males compete,” says Heidi S. Fisher, postdoctoral researcher in organismic and evolutionary biology at Harvard.

“In some species where females mates with multiple males, groups of sperm join forces in order to outswim their uncooperative competitors. We’ve shown that in deer mice, cooperation only occurs among close relatives — sperm from the same male,” she adds.

This ability of sperm to discriminate between related and unrelated sperm is not seen in monogamous species, in which sperm of different males are unlikely to ever interact.

The results suggest that competition among males drives cooperative behaviour among their sperm.

“This finding that sperm can discriminate suggests that sperm may be much more complex than we’ve appreciated,” says Hopi E. Hoekstra, professor of the Natural Sciences at Harvard.

“Because more than 95 percent of mammals are promiscuous, it’s possible this ability to discriminate and cooperate may be fairly widespread.”

Fisher and Hoekstra found that one mouse’s sperm can even discriminate against that of its brother, suggesting that the recognition system must be very fine-tuned.

Fisher and Hopi E. Hoekstra studied sperm from two species of deer mice, Peromyscus polionotus and Peromyscus maniculatus.

Although closely related, these two species differ greatly in their sexual behaviour: P. polionotus is monogamous, while P. maniculatus females are promiscuous, mating with successive males as little as one minute apart.

The scientists found that only sperm from the promiscuous species showed the ability to discriminate between closely related and more distantly related sperm.

When sperm from different P. polionotus males was combined in a Petri dish, it showed no selective aggregation, says a Harvard release.

Fisher and Hoekstra say it’s not yet clear exactly how sperm identifies its relatives.

The work was published in Nature.