Female promiscuity changes sperm production in male fish, study finds

Male sperm competition was examined using 29 varieties of cichlid fish from Lake Tanganyika in Zambia. Some cichlids are monogamous, while others have multiple sexual partners.

The report of the four-year study was authored by McMaster graduate student John Fitzpatrick, now at the University of Western Australia, and Sigal Balshine, a professor of psychology, neuroscience and behaviour at McMaster.

“We had a digital video camera stuck onto a microscope to measure sperm in real time,” said Balshine. “We found that the species in which the female was promiscuous, the sperm swam faster ... was also longer and swam for longer periods.”

Computer technology was used to track the changes in sperm over time in response to female behaviour.

“Just like a mechanic could make a car drive faster by installing a better engine, evolution appears to act first on the engine that drives sperm movement,” Fitzpatrick said in a release.

Balshine said, “Slow, short sperm was ancestral and evolved to become fast, long sperm.”
“What is new and exciting about our results is this is the first evidence that female behaviours influences sperm swimming speeds.”
Balshine plans to examine the biochemical changes that make cichlid sperm swim faster and longer.

The study’s findings have broad application.
Sperm competition also exists in mammals, insects and birds, said Balshine.
And sperm competition exists in male humans as well. It occurs when a woman mates with multiple partners in a short period of time, resulting in competition between different males sperm in her body to fertilize her eggs.
Balshine said just as with cichlid fish, the speed of human sperm has also been shaped by this human behaviour.

(Hamilton Spectator)