Scientists have found that sperm benefit from working together while swimming to the egg, and this can lead to improved IVF treatments.
Traditionally, the sperm has been viewed as nature’s ultimate athlete, destined to win a race of millions to be the first to reach the egg cell, fertilize it and pass on its genes.
However, scientists have discovered that the most successful sperm don’t operate alone, but cooperate as they navigate to the egg – and knowing how to do it can lead to better IVF treatments.
Researchers have identified biological benefits for sperm working together that may have implications for fertility studies.
It turns out that sperm literally “pucker” as they swim against a stream of thick fluid on their way to the egg.
They often team up to navigate the female tract of many mammalian species, scientists say. They reported in the science journal Frontiers in cell and developmental biology about the reasons why sperm connect.
The physics of how they navigate to an egg in mammals, including humans, is now well understood.
Scientists have found that sperm tend to — in a no-nonsense way — clump together as they “swim” through the thick, elastic fluid of the female reproductive tract.
“This may resemble the peloton formation found in bicycling, although the flow mechanics for sperm are drastically different from those of bikers,” said Dr. Chih-kuan Tung, co-author of the article and associate professor of physics at North Carolina A&T State University.
The scientists used bovine semen – similar to human semen – and a device mimicking the structure of the female reproductive tract to observe how well the sperm, held together in the thick, elastic fluid, swam against different currents.
The researchers found three biological advantages for sperm to pool together as opposed to swimming alone to the egg.
In the absence of electricity, the pooled sperm swam in a straighter line; Against a light or medium current, the sperm were better aligned, like a school of fish moving upstream; and against a strong current the heaped sperm were less likely to be carried away.
“Our discovery of the biological benefits of sperm pooling suggests that in at least part of the female reproductive tract, it’s good for sperm to cooperate with each other,” said Dr. tung
The findings that sperm cooperate surprise Dr. Edgar V. Mocanu, a consultant obstetrician and gynecologist from Dublin’s Rotunda Hospital and the Royal College of Surgeons of Ireland, did not.
“The ejaculate contains millions of sperm,” said Dr. Mocanu, a specialist in reproductive medicine and surgery.
“The mission is not a lone missile, but a formation of fighter jets.
“The purpose is not to find a lonely egg, but to reach the fallopian tubes and patiently wait for the egg to appear.
“Sperm competence is not in speed but in sustained progression to the tubes, so swimming in formation makes a lot of sense.”
Human infertility is a male problem in a third of cases, said Dr. Mocanu, and in the woman in another third. The cause of the rest is unknown.
He believes this new understanding of how sperm work together could lead to new, better methods of treating infertility.
This can be achieved, said Dr. Mocanu, “by potentially identifying better ways to analyze a semen sample, better ways to assess sperm ‘ability’ to swim in vitro, and also improving the selection of the most competent sperm for assisted reproductive treatments.”
dr Tung said, “We certainly hope that the knowledge we provide here will lead to a better diagnosis of male infertility.”