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Female Ducks Develop Complicated Genitals to Outwit Aggressive Males

Rape is a monstrous violation of a woman's freedom. But in a patriarchal society with lopsided values, there seems to be no escape from it//. But ducks seem to show a way out.

Females in certain species have developed complicated genitals that frustrate aggressive male ducks, scientists have found.

A team of biologists at Yale University in Connecticut and the University of Sheffield in Britain stumbled upon the astounding biological answer to rape when they were trying to figure out why some species of birds had penises and some did not.

"Birds are the only group where it mostly has been lost -- 97 percent of birds do not have phalluses at all," Patricia Brennan said in a telephone interview.

"So if it is such a handy tool, why don't they have them any more?" Brennan asked.

Instead, they mate using what biologists call a "cloacal kiss" -- a brief touch of the single opening that birds of both sexes have for disposing of waste and that both eggs and sperm come out of.

Brennan noted that in many species, females choose a mate after he puts on an elaborate courtship display, and breeding pairs are often monogamous.

An exception is ducks -- especially mallards. Although mallards pair off to mate, females are often raped by stray males.

Still the ducklings born of consensual sex seem to be the norm. That was puzzling and so Brennan's team looked at a lot of duck bottoms.

What they found surprised them -- corkscrew-shaped oviducts, with plenty of potential dead-ends.

"Interestingly, the male phallus is also a spiral, but it twists in the opposite, counterclockwise, direction," said Yale ornithologist Richard Prum in a statement.

"So, the twists in the oviduct appear designed to exclude the opposing twists of the male phallus. It's an exquisite anti-lock-and-key system."

Brennan believes females evolved convoluted oviducts to foil the male rapists. Dr. Brennan argues that elaborate female duck anatomy evolves as a countermeasure against aggressive males. “Once they choose a male, they’re making the best possible choice, and that’s the male they want siring their offspring,” she said. “They don’t want the guy flying in from who knows where. It makes sense that they would develop a defense.”

Dr. Brennan suspects that the female ducks can force sperm into one of the pockets and then expel it. “It only makes sense as a barrier,” she said.

To support her argument, Dr. Brennan notes studies on some species that have found that forced matings make up about a third of all matings. Yet only 3 percent of the offspring are the result of forced matings. “To me, it means these females are successful with this strategy,” she said.

Dr. Brennan suspects that when the females of a species evolved better defenses, they drove the evolution of male phalluses. “The males have to step up to produce a longer or more flexible phallus,” she said.

"You can envision an evolutionary scenario that, as the male phallus increases in size, the female creates more barriers. You get this evolutionary arms race," Brennan said.

Only if the female is relaxed and cooperative can the male's sperm get anywhere near the unfertilized eggs, the researchers suggest.

"What I think is really cool is this does speak a lot about the ability of the female to have these cryptic mechanisms of choice," Brennan said.


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