Female promiscuity raises quality of sperm in her mates: study

January 21st, 2009 - 12:33 pm ICT by IANS  

Toronto, Jan 21 (IANS) Female behaviour determines the quality and quantity of sperm of her mating partner, says a new Canadian study.If she is promiscuous, she can trigger changes in the quality and quantity of sperm of a male as he has to compete with other males to impregnate her.

Only if he can produce better, larger and faster sperm than others does he stand a chance of impregnating her, says the study on fish by McMaster University at Hamilton near here.

The study says the idea that sperm would evolve to become more competitive when males compete for fertilisation seems obvious, but there has been little proof of this till date.

Its conclusions are based on the competition for reproduction among species of African fish that influences the sperm of suitors.

These fish exhibit diverse mating behaviours, ranging from strict monogamy to mating with many males in quick succession, a university statement said.

Sigal Balshine, study author and associate professor in the department of psychology, neuroscience and behaviour at the university, said: “In promiscuous species, we found that males produced larger and faster sperm than in closely related species that were monogamous.

“This research offers some of the first evidence that sperm has evolved to become more competitive in response to females mating with multiple males.”

Balshine said female promiscuity becomes a challenge for males when they have to compete with rival suitors to impregnate her.

As part of their study, researchers collected males from 29 closely related species found off the Zambian shores of Lake Tanganyika. They examined the relationship between promiscuity and sperm quality and then used computer simulations to assess how sperm evolved in these fish.

“Our analysis confirmed that sperm became more competitive only after a species shifted their mating behaviours to become more promiscuous,” the statement quoted study leader John Fitzpatrick as saying.

He said: “The first step in producing more competitive sperm was by influencing how much energy the sperm can produce. 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.”

The study has been published in the Proceedings of the National Academy of Sciences of the US.

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