Ostrich penis clears up evolutionary mystery : Nature News & Comment
A long-running question about how the largest species of birds achieve erect penises seems to have been settled. In a study published this week in the Journal of Zoology1, researchers report that male ostriches and emus enlarge their penises using a burst of lymphatic fluid rather than a blood vascular system like that found in reptiles and mammals.
The finding, based on dissections, matches what is known about other species of birds — only 3% of which have penises — and could have important implications for the understanding of the shared, and divergent, evolutionary heritage of birds and reptiles.
The ostrich is one of very few birds to have a penis.
Reproductive rarity
Ostriches and emus are members of the ratites, a group of flightless birds that also includes rheas and kiwis. All male ratites sport penises — as do ducks and some other species — but most birds mate instead with a brief ‘cloacal kiss’, during which the male passes sperm to the female through the cloaca, the same port used for excreting waste.
The existence of a lymphatic penis in some birds presents an evolutionary puzzle, says Richard Prum, an ornithologist at Yale University in New Haven, Connecticut, and co-author of the paper. “What is weird about birds is that they evolved not just a new structure, but a novel way to do something that was already being done,” he says.