Wednesday, 31 May 2017

Traumatic beetle sex causes rapid evolutionary arms race

24 May 2017

By Chris Simms

Ever wondered what constitutes extreme sex? Cowpea seed beetles certainly know – their sexual act is brutal, and it also seems to encourage a rapid evolutionary arms race between spiked penises and shielding tissue in females.

Extreme genital co-evolution happens in many types of animal, including ducks, fish and fruit flies. For example, female ducks of some species have evolved long and complex internal genitalia, complete with blind alleys, to thwart the unwanted advances of males intent on fowl play. And to counteract this, male ducks have evolved longer and more elaborate penises.

Now Liam Dougherty of the University of Western Australia and his colleagues have discovered how female cowpea seed beetles (Callosobruchus maculatus) are fighting back against the males’ vicious spiked penises (see picture, below).

Once beetles become sexually mature after emerging from the beans in which they live as larvae, they have only one thing on their to-do list – procreation. They don’t eat, or drink, they just look for partners.

“There’s not much courtship,” says Dougherty. “The smaller male jumps on the female and there’s a bit of a struggle. He sort of leans back when he’s fully in. Then there’s a period when the female starts kicking the male. Then they break apart after a few minutes.”
Sexual healing

To peek into what’s happening beneath the shells, Dougherty and his colleagues looked at female sex-related damage in 13 independently bred populations of the beetles. At first, they saw no link between scarring and the thickness of female reproductive tracts. But when male spike length was taken into account, it revealed that scarring was greatest when linings were thin and penis spikes were long.

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