A chick embryo's developing penis (colored red) prior to regression.A.M. HERRERA AND M.J. COHN, UNIVERSITY OF FLORIDA
Males of species that practice internal fertilization generally use phalluses to insert gametes into females’ reproductive tracts. But 97 percent of bird species have lost the ability to grow a penile structure capable of penetration over the course of evolution. They mate instead by rubbing together small openings called cloacae, in a maneuver called a cloacal kiss. Reported in a study published yesterday (June 6) in Current Biology, researchers have identified a gene responsible for repressing the development of phalluses in bird species.
The authors began their studies by comparing development in chickens and quails, which lack substantial phalluses, to development in ducks and geese, which mate through penetration. They found that chickens and quails grow a small nubbin called a genital tubercle during development, ...
