The only known animals in which the female has a penis and the male has a vagina have been discovered. Kazunori Yoshizawa from Hokkaido University in Japan, Rodrigo Ferreira from the Federal University of Lavras in Brazil, and Charles Lienhard in Geneva are responsible for the discovery. The research was published in the April 17, 2014, edition of the journal Current Biology.
Four distinct but related species of cave-dwelling insects (Neotrogla) were discovered in caves in Brazil. The female Neotrogla bear the young but the males have a small vagina while the females have an elaborate penile structure. This is the first discovery of a sex-role reversal in animals that includes an elaborate penis in the female of the species and a vagina in the males.
The penile structure in Neotrogla includes numerous spines and an inflatable chamber that allows the copulating insects to remain attached. The insects were observed by the researchers to copulate for as long as 70 hours. The males provide both sperm cells and nutrition to the female during copulation.
There are many other examples of sex-role reversal in animals but no animal has ever been discovered that exhibits an exchange of physical sexual characteristics to the extent observed in Neotrogla. The researchers propose that the cave environment may have played a role over the eons in the adaptation that works best for Neotrogla. The nutrient and mineral composition of the isolated environments may have also contributed to the sex-role reversal in the four species of Neotrogla.
Biology and evolution have no concrete explanation for the existence of two sexes in animals. The researchers propose that this discovery may produce new insights into sexual selection, the evolution of novel species, and the role of conflict between the sexes. Nothing may come from this discovery but the fact that Neotrogla is the only species known in which the female has a penis.