An insect species living in remote caves of Brazil has reversed the usual male-female actions in reproduction, scientists say. With the females possessing a penis-like sex organ with which they penetrate the males.
The flea-sized insects of the genus Neotrogla have the distinction of being the first example ever found of a species with sex-reversed forms of genitalia.
While so-called "pseudo-penises" have been seen in females of some other species, in each of them the male must still penetrate the female during mating.
Only Neotrogla has truly reversed that paradigm, the females using their organ, dubbed a gynosome, to penetrate the male and gather sperm during reproduction.
"The relative function and pattern of elaboration of male and female genitalia in Neotrogla are completely reversed relative to that generally observed," the researchers say.
However, since the male is still the provider of sperm, it is still doing the fertilizing despite the reversal of sex organ configurations.
And as if the organ swap wasn't distinctive enough, the sex sessions, with spines on the female's gynosome holding the male fast, can last from 40 to 70 hours, the researchers report in the journal Current Biology.
The connection between female and male during reproduction is so strong, the researchers reported, that when they attempted to separate a mating female and male, the abdomen of the male was torn from its thorax while the genital connection held fast.
The sex organs and role reversal may be an evolutionary result of the resource-poor environment of the insects' cave homes. With the males providing females with nutrition in the semen the female takes in. That would make it advantageous for females to take the lead role and mate more often with as many males as possible.
The findings could suggest new study avenues in the areas of sexual selection, the reproductive conflict between the sexes and evolution of new sexual organs and behaviors.
"It will be important to unveil why, among many sex-role-reversed animals, only Neotrogla evolved the elaborate female penis," researcher Yoshitaka Kamimura from Keio University in Japan says .
The scientists say they will attempt to create Neotrogla colonies in labs to conduct further research.
"Further controlled studies of the mating system of Neotrogla species ... would provide an extremely rare opportunity to test the generality and relative importance of some hypotheses about sexual selection," they say.
