Sperm teams swim against the tide more easily

Sperm teams swim against the tide more easily

Coexistence of spermatozoa swimming individually and grouped. Clustered sperm are labeled with yellow ovals. Scale bar: 50 μm. Credit: S Phuyal, SS Suarez, CK Tung

It turns out that sperm go against the current better when they swim together.

Despite the popular idea that the fastest and most adapted male reproductive cell is the one that wins the race to fertilize, research has shown that sperm often team up to navigate the female reproductive tract in a large range of mammal species. A new study published in the journal Frontiers of cell biology and development offers compelling reasons behind newly identified clustering behavior.

Previous research by the team, led by scientists from North Carolina A&T State University and Cornell University, found for the first time that sperm naturally come together without attaching themselves to each other. to others when swimming in a viscoelastic fluid. This is the type of fluid encountered by sperm migrating through the cervix and uterus to the oviduct where the egg is fertilized. The term viscoelasticity refers to both thickness and elasticity.

However, teams of unattached sperm do not overtake solitary swimmers, as they do in other examples of group behavior. For example, the wooden mouse sperm head has a hook that physically attaches it to other sperm, linking hundreds to thousands in a kind of sperm train faster than single sperm.

Against a current

The researchers wanted to know about the possible biological benefits of this seemingly strange behavior on a scale and in a setting that is difficult to study, particularly viscoelastic fluid currents flowing through narrow channels in the female reproductive tract. In a series of experiments using bovine sperm (a good model for the human variety) and a microfluidic device to mimic the physical parameters of the female tract, they observed how sperm pooled in a viscoelastic fluid responded to different flow scenarios. .

They found three potential biological benefits to sperm clustering, based on the strength of the current against which the sperm must travel. First, in the absence of flow, clustered sperm seem to change direction less frequently and swim in a straight line. Against a light to medium flow, the grouped sperm are better aligned, like a school of fish moving upstream. Finally, under high physiological flows, there seems to be a safety in the number against the outburst by the strong flow.

“Generally, I would say that identifying motility benefits that are not speed enhancement is not usual, and therefore significant. sperm,” noted co-author Dr. Chih-kuan Tung. and associate professor of physics at North Carolina A&T State University.

Fertility needs physical

As a physicist by training, Tung said he was particularly intrigued by the shielding dynamics at play when the flow is heaviest. “It may be similar to peloton formation in cycling, although the fluid mechanics for sperm are radically different than for motorcyclists. We would definitely like to know more about that.”

Watching sperm swim isn’t just a scientific sport. Better understanding the physics of how sperm navigate the complicated female reproductive system to fertilize the egg may have implications for infertility treatments and beyond.

“Longer term, our understanding may provide better selection of sperm used for interventions such as in vitro fertilization or other assisted reproductive technologies,” Tung said. “This may be necessary because [these methods] generally ignore some or all of the selection mechanisms present in the female tract and yield less favorable results.”

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More information:
Biological benefits of the collective swimming of spermatozoa in a viscoelastic fluid, Frontiers of cell biology and development (2022). DOI: 10.3389/fcell.2022.961623

Quote: Teams of sperm swim more easily against the current (2022, September 22) retrieved September 22, 2022 from https://phys.org/news/2022-09-teams-sperm-smoothly-current.html

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