New study discovers that sperm work together in “pacelines” to fertilize egg

Sperm team up in two-four cell packs and work together to reach the finish line, scientists have discovered. Chih-Kuan Tung at North Carolina Agricultural and Technical State University says the new information goes against previous theories that it was every man for himself when it comes to conception.

Rather, sperm cells will often form alliances within the female reproductive tract to swim upstream.

“Sperm have often been represented as individuals racing against each other to fertilize an egg, but these portrayals have been based on flat views of microscope slides and other laboratory settings that don’t reflect their natural context,” Tung said.

According to a New Scientist article, when Tung’s team created a three-dimensional mock-up of the female reproductive tract, bull sperm seemed to create small squads of two to four cells, working together to travel through the vaginal mucus.

At first, the fact that the sperm would “work together” confused the team. “In biology, when cells and structures do something, they should probably get something out of it. So that became the question we were asking ourselves: what are these sperm getting out of it?” Tung asked.

The scientists conducted an experiment by injecting bull sperm into a silicone tube with thick fluid. They then used a syringe pump to create two different speeds of flow. When there was no increased flow, groups of sperm would push through the fluid better than an individual. Much like a group of cyclists working together in a headwind.

Tung said that in the increased flow scenario, sperm would change their positions within the clusters. As New Scientist reported, “The arrangement resembles how cyclists ride together in a peloton so they encounter less air resistance.”

“It could be this kind of mechanism that just allows that at least some of them will eventually get to the oviducts,” Tung said. “Because without this, maybe none of them actually could, because of the strong flow of uterine fluids.”