Evolution of genital morphology in waterfowl

Here is the PLOS paper on the topic; here is the NY Times article summarising the results; via Carl Zimmer.

 Dr. Brennan was oblivious to bird phalluses until 1999. While working in a Costa Rican forest, she observed a pair of birds called tinamous mating. “They became unattached, and I saw this huge thing hanging off of him,” she said. “I could not believe it. It became one of those questions I wrote down: why do these males have this huge phallus?”

That passage reminded me of Amitav Ghosh‘s In an antique land, in which, he recounts his first encounter with the duck (or geese) genitalia, and how his surprise was misconstrued by his informants for naivette, and how the incident led to the breaking of ice between him and his informants; unfortunately, I do not have my copy of Antiuqe Land handy to quote the relevant passages.

Anyway, here is the answer to the question in the quote above:

“Basically, you get a bigger phallus to put your sperm in farther than the other males,” Dr. Brennan said.

Dr. Brennan realized that scientists had made this argument without looking at the female birds. Perhaps, she wondered, the two sexes were coevolving, with elaborate lower oviducts driving the evolution of long phalluses.

And, why do female birds have elaborate oviducts?

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.

A very interesting piece: take a look!