"War Between the Sexes:" The Co-evolution of Genitalia in Waterfowl

http://opa.yale.edu/news/article.aspx?id=2050 --- According to the study, in various independent lineages of ducks females developed more elaborate oviducts as males evolved longer phalluses. In other lineages females lost oviduct complexity as the phallus evolved toward smaller size. Why all this dynamic evolution? Brennan hypothesizes that the female waterfowl have evolved these unique anatomical features as physical counter-measures to evade male attempts to assert control over reproduction. "Despite the fact that most waterfowl form monogamous pairs, forced copulations by other males — the avian equivalent of rape — are common in many waterfowl," said Prum. "The length of the phallus of a species is strongly correlated with the frequency of forced copulations." "In response to male attempts to force their paternity on females, female waterfowl may be able to assert their own behavioral and anatomical means of controlling who fathers their offspring," Brennan said.



Evolution of convolutions in the Mallard oviduct (left) and phallus (right) may give the female duck an anatomical means of controlling who fathers their offspring. Bar measure cm. (Courtesy of Patricia Brennan)