Instead of boosting speed, grouping helps male reproductive cells travel in a uniform direction
© James Weaver/Wyss Institute/Harvard Univ.
Mouse sperm shoot along straighter paths by ganging up. Yet the merits of forming flocks evaporate if the group becomes too large, researchers report July 22 in the Proceedings of the Royal Society B.
“Sperm aggregation is one of the more enigmatic adaptations to sperm competition,” says evolutionary biologist Dawn Higginson of the University of Arizona in Tucson.
Sperm competition arises when a female mates with multiples males, and though cooperative behavior in sperm is rare, examples appear across the animal kingdom — from great diving beetles to possums. Controversy looms over whether sperm herding provides a competitive advantage over swimming solo. In desert ants (SN: 7/26/14, p. 20) and Norway rats, sperm crews swim faster, but in some species like the house mouse,