Like salmon travelling upstream to spawn, sperm cells are extremely efficient at swimming against the current, said a study that could help scientists design new diagnostic tools and more efficient artificial-insemination techniques.
At certain flow speeds, the sperm cells were able to swim very efficiently upstream, the researchers discovered.
"We found that if you create the right flow velocities, you can observe them swimming upstream for several minutes," said Jorn Dunkel, an assistant professor of mathematics at Massachusetts Institute of Technology (MIT).
The mechanism is very robust, Dunkel added.
Of the hundreds of millions of sperm cells that begin the journey up the oviducts, only a few hardy travellers will ever reach their destination.
Not only do the cells have to swim in the right direction over distances that are around 1,000 times their own length, but they are exposed to different chemicals and currents along the way.
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In a bid to understand what the cells are capable of, the researchers built a series of artificial microchannels of different sizes and shapes, into which they inserted the sperm.
They were then able to modify the flow of fluid through the tubes, to investigate how the cells responded to different current speeds.
The study will appear in the journal eLife.