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Too much sex can alter shape of genitals, beetle study shows

"It takes two to tango, so when changes in shape in one sex leads to corresponding changes in the other sex this is known as co-evolution," said researcher Megan Head.

By Brooks Hays
Sexual conflict between male and female burying beetles leads to evolving genital shapes. Photo by gubernat/Shutterstock
Sexual conflict between male and female burying beetles leads to evolving genital shapes. Photo by gubernat/Shutterstock

EXETER, England, May 20 (UPI) -- Genital shape and size vary widely across the animal kingdom. New research into the mating habits of burying beetles reveals an unexpected reason why.

Most research into the evolution of genital diversity has focused on the competition for mates among members of the same sex. But a new study by scientists at the University of Exeter suggests conflict between males and females over the frequency of sex is also a driver of genital adaptations.

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Such competition may explain the growth of penis-like organs and the development of claw-like features on female genitalia.

"It takes two to tango, so when changes in shape in one sex leads to corresponding changes in the other sex this is known as co-evolution," researcher Megan Head explained in a news release.

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Males tend to prefer as much sex as is physiologically possible, as each instance increases their odds of passing along their genes. A female, on the other hand, can only get pregnant once each time. For female burying beetles, an excess of male partners may also diminish their ability to provide parental care.

To test the role of sexual conflict in co-evolutionary changes, researchers observed ten generations of burying beetles. One group of beetles was selected for low mating rates and another was selected for high mating rates.

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The group that mated at a high rate featured longer male genitalia and female genitalia with more pronounced claws after ten generations.

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The researchers detailed their findings in the journal Evolution.

"Our research demonstrates the general importance of conflicts of interest between males and females in helping to generate some of the biodiversity that we see in the natural world," explained Paul Hopwood, a researcher at Exeter's Centre for Ecology and Conservation. "It's fascinating how genital evolution can happen so fast -- in ten generations -- showing how rapidly evolutionary changes can occur."

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