Sperm swim differently to how we thought. Rather than undulating their tails symmetrically, like an eel, they have a lopsided wiggle that combines with spinning about their long axis to give an overall forward motion.
鈥淭he asymmetry cancels out because of the rotation,鈥� says Hermes Gad锚lha at the University of Bristol, UK. 鈥淭hey are like otters when they swim in a corkscrew motion.鈥�
Human sperm were some of the first living cells to be seen under a microscope, by Dutchman Anton van Leeuwenhoek in 1677, when he viewed his own sperm retrieved after sex with his wife. The scientist later described them as having a 鈥渟nakelike movement, like eels in water鈥�. And this view persisted until now.
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Gad锚lha鈥檚 team has made the best yet video of a sperm鈥檚 motion, by using a 3D camera recording at 55,000 frames a second combined with a microscope that moves the sample up and down very fast so all different parts of the tail come into focus.
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This showed that the whip-like tail beats asymmetrically, in that it only wiggles to one side. Alone, this would send the sperm swimming in circles 鈥� but the second aspect of sperm movement, spinning about their long axis, ensures they travel forwards.
鈥淚magine you could only swim with one leg 鈥� you would swim in circles,鈥� says Gad锚lha. 鈥淏ut if you rotated from one side to another as you swam, you would balance out the asymmetry of your stroke.鈥�
The finding solves a puzzle, as the molecular machinery inside a sperm that makes its tail move is asymmetrical and it wasn鈥檛 known how this could produce the presumed symmetrical tail motion.
A better picture of how sperm move could help us understand聽male infertility聽caused by sperm that can鈥檛 swim well, says Gad锚lha.
Science Advances
