Scientists have discovered cave insects in Brazil that exhibit a bizarre type of sex reversal. Unlike most insects, the females of these strange insects have spiny "penises" while the males have "vaginas."
The cave-dwelling insects studied by an international team of researchers belonged to four distinct yet related species from the genus Neotrogla. The discovery also marks the first time that scientists have identified an animal with sex-reversed genital organs.
"The female penis is a completely novel structure," Hokkaido University entomologist Yoshizawa Kazunori told The Verge. Except for producing the larger gametes and having an egg-laying apparatus, the females in these four species of winged insects, called Neotrogla, seem to have become "very masculine" over evolutionary time, Kazunori added. The appearance of such a novel structure is exceptionally rare, he said, and "may be comparable with the origin of insect wings." Kazunori is also one of the co-authors of a paper published in the online journal Current Biology.
A researcher named Rodrigo Ferreira from the Federal University in Brazil was conducting studies on the insects in their native cave habitats. After Ferreira sent a few samples to another insect expert in Geneva, the insects were identified as part of a new genus. Japanese researchers then joined the effort to conduct further studies in Neotrogla.
With sex-reversed genitalia, it goes without saying that these insects have relatively bizarre sex lives. However, things get even stranger since the insects' passionate sexual escapades can last around 40 to 70 hours.
"Although sex-role reversal has been identified in several different animals, Neotrogla is the only example in which the intromittent organ is also reversed," Kazunori said.
During the act of copulation, the female insects would insert their complex, phallus-like genitals into the males' vagina-like sex organ in order to extract the male's sperm. The researchers have come up with a number of theories to explain the strange sexual organs and habits but current speculations lean towards an evolutionary reaction to the scarcity of resources in the insects' environment.
Since these insects live in caves, the act of copulation provides the females with an extra bonus in the form of nutrient rich semen. The extraction process used by the females means that little of the nutritious fluids will be wasted. The extra nutrition gained during intercourse is also another reason why the females attempt to mate more often.
"It will be important to unveil why, among many sex-role-reversed animals, only Neotrogla evolved the elaborated female penis," said Yoshitaka Kamimura from the Keio University in Japan.
