Bull sperm move their tails up and down with a larger range of motion when the fluid around them is more viscous, which could help them reach an egg
By Jason Arunn Murugesu
1 November 2023
Researchers studied bull sperm, which have similar structures and swimming patterns to human sperm
DR T E THOMPSON/SCIENCE PHOTO LIBRARY
Sperm change how they swim in response to different conditions in the vaginal tract. The ability to adjust to these conditions could be a measure of sperm health. If this is shown in future research, the most adaptable sperm could one day be selected for fertility treatments to maximise the chance of conceiving.
“The female reproductive tract is a complex environment that plays a critical role in influencing sperm migration behaviour to ultimately select high-quality sperm for natural fertilisation,” says Farin Yazdan Parast at Monash University in Melbourne, Australia.
After vaginal intercourse, mucus secretion into the fallopian tubes intensifies, she says. This stimulates fluid movement in the vaginal tract, making it more viscous.
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Previous studies into how sperm change their swimming styles to navigate these tracts separately considered factors such as the sperm’s shape and the viscosity and flow of the fluid they swam through, says Yazdan Parast. To better understand the collective conditions sperm face, she and her colleagues wanted to study these factors together.
The researchers filled a container with a mucus-like liquid, similar to that in the vagina, which they could manipulate to be more or less viscous.
They then attached a bull sperm cell to a tiny chamber in the container to observe how it changed the way it moved its tail as the team altered the viscosity of the liquid. Bull sperm have a similar structure and swimming pattern to human sperm, but it is easier to gain regulatory approval to study them, says Yazdan Parast. The experiment was repeated for nine other bull sperm cells.