Yale researchers have found that some female duck genitalia is evolving, forming clockwise spirals, to avoid impregnation from undesirable yet aggressive males.
The study builds upon a finding by Yale in 2007 that first noted how duck's sexual organs had been morphing. While most birds are phallus-free, ducks are oddly endowed--up to 8 inches. Using high-speed video they found that ducks could go from zero to happy in less than half a second.
That endowment should give the males an advantage during forced mating but these Viagra-free males aren't out of the woods yet.
"In species where forced copulation is common, males have evolved longer penises, but females have coevolved convoluted vaginas with dead-end cul-de-sacs and spirals in the opposite direction of the male penis," said Patricia L.R. Brennan, a researcher in the Yale Department of Ecology and Evolutionary Biology.
Yale researchers tested the theory by examining duck penis eversion in a series of glass tubes. As expected, a straight tube or one that has counter-clockwise spiraling doesn't slow down the process. The tubes that mimicked the clockwise spiral completely halted the eversion.
"This coevolution results from conflict between the sexes over who is going to control fertilization," Brennan added.
"Although we predict that sexual conflict should be ubiquitous, finding a system where the 'arms race' between the sexes is so dramatic is exceedingly rare. Ducks are providing us with an incredible opportunity to understand the evolutionary consequences of conflict," said Brennan.
Why Yale decided to study duck penises in the first place I will never know.
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