Watching These Sperm Cooperate Is Oddly Fascinating

Get your Sunday started right by watching how sperm sometimes form power-swimming blocks to get ahead. And learn why these particular sperm get together.

We all heard the talk, in sex ed classes, about how each of us is a lottery winner. Out of every spermatozoon in a typical, ah, emission, we were the one that made it. But not every sperm is a lone swimmer trying to be the 100-million-to-one odds. There are some cases in which it’s better to cooperate, like if the sperm are swimming in the body of a female who has had sex with more than one partner.

The highly cooperative sperm above are actually those of a deer mouse. Female deer mice often have more than one partner. The sperm of male deer mice, scientists found, often form “motile aggregations” — those are the large white clumps of sperm that you can see in the video going much faster than smaller groups of sperm.

Each individual sperm gets an advantage in these aggregations, so why don’t they all group up? Because in this case, the individual sperm cells come from different males. It doesn’t pay to help someone who doesn’t share your genes. In mixed company, sperm cells are much more likely to form motile aggregations with sperm from the same mouse.

In mouse species that don’t tend to have multiple partners, sperm cells will group up with any other sperm cell, regardless of origin. It’s only in — and I’m using the study’s words — “promiscuous” populations that sperm cells team up only with other cells from the same source.

[Source: Competition drives cooperation among closely related sperm of deer mice]