Sept. 30, 2022 -- The adage that the fastest, strongest sperm is the one that fertilizes the egg is being called into question after new research suggested that teamwork is a more powerful reproductive driver than survival of the fittest.

It is a long, challenging swim through the female reproductive tract that male sperm navigate, and they have a much better chance of reaching the egg if they swim together in clusters, report researchers from North Carolina A&T State University and Cornell University. 

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

Sperm, like schools of fish,  swim independently, but move in and out of the group along the way. To find out whether this collective swimming had any actual biological benefit, the scientists did experiments using bull sperm, which shares similar properties with human sperm.

The sperm were placed in a device that mimicked the physical environment of the cervix and uterus, and then the scientists tested how the sperm responded when they switched up the properties of the fluid and flow. They discovered three benefits to sperm traveling in clumps instead of going it solo and published the findings in Frontiers in Cell and Developmental Biology.

When the fluid is static, without any flow at all, the sperm can more effectively swim in a straight line when grouped together. At a moderate level of flow, clustering helps the sperm in aligning with one another so they can swim against the current much like a school of fish swimming upstream. When the flow is strongest, sperm are less likely to get carried away by the current if they're swimming together.

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

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SOURCE:

Frontiers in Cell and Developmental Biology: "Biological benefits of collective swimming of sperm in a viscoelastic fluid."

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