There’s a reason sperm swim together

September 30, 2022 – The adage that the fastest and strongest sperm fertilizes the egg is being called into question after new research suggests teamwork is a stronger driver of reproduction than survival of the fittest.

It’s a long, challenging swim through the female reproductive tract that male sperm navigate, and they have a much better chance of reaching the egg when they swim together in groups, researchers at North Carolina A&T State University and Cornell University report.

The researchers observed that sperm swim together in groups as they make their way through the thick but elastic fluid of the cervix, uterus and fallopian tubes on their way to the egg.

Sperm swim independently, like schools of fish, but move on their way in and out of the group. To find out if this collective swimming actually has any biological benefit, the scientists conducted experiments using bull semen, which has properties similar to human semen.

The sperm were placed in a device that mimicked the physical environment of the cervix and womb, and then the scientists tested how the sperm responded when they changed the properties of the fluid and flow. They discovered three benefits of sperm traveling in clumps rather than doing it alone published the findings in Frontiers in cell and developmental biology.

When the liquid is static, without any flow, the sperm can swim in a straight line more effectively when they are grouped. With a moderate current, clustering helps sperm align with each other, allowing them to swim against the current, much like a school of fish swimming upstream. When the current is at its strongest, sperm are less likely to be swept along by the current as they swim together.

The researchers’ discoveries about sperm movement can be used to better understand why sperm might not make it and how scientists can improve fertility chances in couples who are struggling to conceive. As more researchers learn about which sperm are most successful in reaching the egg, they can apply these discoveries to assisted reproduction technology to help people conceive.