Everybody knows the shortest distance between two points is a straight line, and now Harvard researchers have evidence that sperm have been taking the familiar axiom to heart. Though competition among individual sperm is usually thought to be intense, with each racing for the chance to fertilize the egg, Harvard scientists say that in some species, sperm form cooperative groups that allow them to take a straighter path to potential fertilization.
A new study, conducted by Heidi Fisher, a postdoctoral student working in the lab of Hopi Hoekstra, the Alexander Agassiz Professor of Zoology in the Museum of Comparative Zoology, and postdoctoral student Luca Giomi, who works with L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, professor of organismic and evolutionary biology, and of physics, shows that in Peromyscus maniculatus, a species of deer mouse known to be promiscuous, sperm clump together to swim in a more linear fashion. The study is described in a July paper in Proceedings of the Royal Society B. “We generally think that each individual sperm cell swims its little heart out to get to the egg. But it had been discovered that, in at least a handful of organisms, sperm will cooperate and swim as a group,” said Hoekstra, who is also a professor of organismic and evolutionary biology.
The new paper builds on a 2010 study conducted in Hoekstra’s lab, which found that sperm cells preferentially clump with those produced by the same male. Spurred by that earlier paper, Mahadevan approached Hoekstra with the idea of creating a mathematical model to understand whether and how sperm received an advantage by forming groups.