Security Arms Races in Duck Oviducts and Phalluses
Interesting research at Yale:
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.”
Female ducks seem to be equipped to block the sperm of unwanted males. Their lower oviduct is spiraled like the male phallus, for example, but it turns in the opposite direction. 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.