Scientists have discovered the first female “penis” in the animal kingdom, a new study says.
Four new species of Brazilian cave-dwelling bugs have sex-reversed genitalia, so that the female uses her elaborate penis-like organ to penetrate the male’s vagina-like opening and collect his sperm. (Related: “Wild Romance: Weird Animal Courtship and Mating Rituals.”)A female in the newfound species N. curvet (top) mates with a male. Photograph by Yoshizawa Kazunori
“There’s nothing that [this] can be compared to,” said study co-author Rodrigo Ferreira, a professor at the Federal University of Lavras in Brazil. “This elaborate female penis is completely unique.”
While there are a handful of other known species in which male genitalia are reduced and the females have penetrating organs, none are so complex or have been shown to be so structurally and functionally similar to a penis, said Ferreira, whose study was published April 17 in the journal Current Biology.
“It was a surprise for all of us,” Ferreira said. “We were completely astonished when we first saw that structure.”
Ferreira and colleagues found the new species after scouring walls and floors of pitch-black caves in Brazil. The animals belong to the little-known Neotrogla genus, which belongs to an order of insects commonly called booklice or barklice.
Interestingly, further study in the lab revealed that each of the four new species has its own slightly different version of the female penis.
In three species, the female penis contains spines that fit species-specific pouches in the male genital chamber, while one species has a strongly curved female penis that matches a curved male chamber.
To figure out whether the female Neotrogla‘s penis-like structure actually acted like a penis, the researchers had to go back to the caves and collect mating insects. (See “Why Sea Slugs Dispose of Their Penises.“)
After observing them in the lab, the team confirmed that the insects’ female penis-like structure, called the gynosome, was indeed used to penetrate the males.
They also found that the insect couples mated for an average of about 50 hours at a stretch—an exceptionally long time among animals. “One of the couples … copulated for around 73 hours—it was really surprising,” Ferreira said. (See “Why Some Animals Mate Themselves to Death.”)
Spikes along the female penis anchored the female to the male so tightly that when the researchers tried to separate them, they inadvertently tore apart the male’s body without affecting the genital coupling, Ferreira said.
He speculated that the females might be forcibly holding on to the males for such long periods to get as much of their sperm and seminal fluid as possible.
Why Reverse Roles?
William Eberhard, an evolutionary biologist at the Smithsonian Tropical Research Institute who was not involved in the study, said the work was “well done” and that it represented “exciting, interesting stuff.
“They’ve convinced me of the reversal of genitalic roles in this species, at least in terms of who goes inside who,” he said. (See “Barnacles Can Change Penis Size and Shape.“)
Such sex-reversed genitalia are extremely unusual, and these insects could potentially be used to test many hypotheses about sexual selection and the evolution of genitalia, he said.
For instance, scientists think that Neutrogla‘s sex-reversed genitalia may arise from a reversal in sex roles resulting from the harsh conditions in which these insects live, study co-author Ferreira noted.
The bugs live in extremely dry and dark cave environments where their food—bat guano (poop) or bat carcasses—is scarce. (See National Geographic’s cave pictures.)
That means eating enough to produce eggs can be a tough task for females without some extra nourishment, which could come from the males in the form of nutritious seminal fluid. “The female penis, in this context, is certainly a good tool for getting a nutritious resource from males,” Ferreira said.
Ferreira has successfully bred three of the species in his lab and is planning to build special chambers to re-create the insect’s subterranean environment. Apart from studying Neotrogla‘s mating behavior in these chambers, he plans to introduce a whole community of cave species to understand the ecology of these insects.
There are likely other interesting cave species that are yet to be discovered, Ferreira added. Some projections suggest that Brazil has more than 150,000 caves, while only around 12,000 are officially known, he said.
“We have a huge country,” he said. “We have thousands of caves that are still unknown, and the animals that live in there are also unknown.”