Enlarge image

Sperm in motion (symbolic image): Different swimming styles depending on the environment

Photo: SCIEPRO / Getty Images/Science Photo Library RF

Crawl, butterfly, breaststroke: Humans have developed numerous swimming styles to move through the water as quickly and effectively as possible. Evolutionarily, however, this form of adaptation is much older. Sperm also master different swimming styles in order to penetrate different fluids as quickly and energy-efficiently as possible. This is the result of an experimental study, the results of which were published in the journal "Cell Reports Physical Science".

Researchers led by Reza Nosrati from Monash University in Melbourne, Australia, have built a "test arena" for bull sperm. This was intended to simulate the environment in the female reproductive canal to which sperm have to adapt on their way to the egg. This is because the female reproductive tract rejects low-quality sperm and prefers those that are actually able to swim to the egg.

An example of such a process: During sexual intercourse, more mucus is secreted in the fallopian tube, the fluid in it moves more strongly. "This flow is intended to prevent pathogens from entering the reproductive tract," the study says. The germs would be flushed out. At the same time, only sperm that are able to swim against the current can reach the egg.

In the »Test Arena«

In the "test arena", the researchers exposed the bull sperm to different flow conditions, experts also speak of shear speeds. In addition, the cells should move in liquids with different viscosities, i.e. toughness. Using high-speed microscopes capable of taking 200 images per second, the experts observed how the sperm swam through the "test arena" using their tails, the so-called flagella.

"With our approach, we were able to investigate how variations in viscosity and shear rate affect sperm behavior at the single-cell level, which was not possible with conventional methods," said Reza Nosrati, lead author of the study.

According to the team, the results show that the flagellation of a sperm is mainly influenced by viscosity and less by shear speed. Especially in a rather thin environment, the energy expended by the bull sperm hardly changed depending on the flow. In viscous fluids, however, it was observed that sperm beat their flagella less strongly when the current intensified.

Sperm management with energy

According to the team, the observations suggest that the cells adapt to different fluid environments. Accordingly, they manage their energy and adjust the manner of their scourges to the external conditions. This "enables efficient swimming against the current," it says.

According to the team, it is currently refining its test procedure for a follow-up study. The planned study – again in animal models – will focus on how the findings could potentially improve artificial insemination procedures.