We thought we had sperm figured out, but it turns out they wiggle in mysterious ways. The finding could shed light on why some men have fertility problems, and lead to more accurate diagnostic tests for infertility.
Sperm move forward by wiggling their long tails, taking several hours to travel from the vagina, through the womb, to reach an egg in the fallopian tubes.
They also have another kind of behaviour, called hyperactivation, when they beat their tails more strongly and asymmetrically. This makes them jerk around randomly and so cover less ground.
Advertisement
We had thought that sperm only switch to this mode when they reach the egg, in order to burrow through its outer wall.
But Stephen Publicover of the University of Birmingham, UK and his colleagues have found that fresh sperm in fact swap repeatedly between normal swimming and hyperactivation. “Rather than starting off in one stroke and ending up in another, they’re switching back and forwards all the time.”
They filmed individual sperm in a dish for three minutes at a time, and found that 16 out of 18 showed these abrupt switches, changing on average every 10 seconds. The findings were presented at the conference in Birmingham in the UK earlier this month.
This suggests that hyperactivation is not just a way of getting inside the egg, says Publicover. But it’s unknown what other purpose it could serve. It’s hard to study human sperm inside a woman’s body, but we have clues from animal research.
Susan Suarez of Cornell University in New York, says hyperactivated sperm in mice seem better at escaping from pockets in the wall of the fallopian tube. “We have never understood well how human sperm travel through the reproductive tract.”
