Curious Case of The Sex Reversed Insects
Credit: Current Biology, Yoshizawa et al.
They say there is nothing new under the sun. But consider this newly discovered genus Neotrogla with four insect species, in the caves of Brazil. The females have the equivalent of the penis; the males have a cavity like the vagina.
Now, wait a minute. Did the researchers simply mislabel the specimens you ask? In biological terms, the female has the bigger gametes — larger, more expensive to produce energy-wise, stationary eggs vs small motile sperm — and is almost always the one who gives birth. Here, the female also has the spiky, penis-like structure called the gynosome, which inflates inside the male’s vagina-like organ. Rather than squirt fluids, it penetrates and draws stuff from the male.
Insects have some peculiar mating rituals. “Nuptial gifts” are not unusual in their world. Male flies bring edible dowry to the female. In bush crickets, along with sperm, males provide nourishing capsules to the female during copulation. But the Neotrogla takes its own sweet time to allow for complete transfer of vital resources. “We could observe a couple that was mating for close to 70 hours,” says co-author Rodrigo Ferreira from the Federal University of Lavras in Brazil, who found and described the species. The average time for copulation is 40 hours.
The Brazilian ecologist sent the specimens to taxonomist Charles Lienhard in Switzerland, who discovered the female’s penis-like organ upon dissection. He identified the new genus. The entomologist Kazunori Yoshizawa from Hokkaido University in Japan joined them to study this cave insect further. All three are co-authors of the paper in this week’s issue of Current Biology.
Sex-role reversal has been identified in many different animals, but Neotrogla is a case where the sex organ is also swapped. In most species, the female is choosy and promiscuous males vie with each other for a chance to pass on their genes. There are anomalies in nature: female African topi antelopes aggressively pursue males; male sea horses carry the fertilized eggs during gestation.
But the gynosome is unique and the secret of this adaptation may lie in the insects’ habitat. All four species of Neotrogla live in dry caves, which are food scarce environments. “This is the main point about them: they live in conditions where only few species can survive. In a habitat with such constraints, gathering resources to produce eggs is a tough task. So, the seminal gift is welcome. The female penis, in this context, is certainly a good tool for getting a nutritious resource from males,” says Ferreira. For now, it appears that the sole purpose of the gynosome is to act like a vacuum cleaner and get all possible nutrients from the male. Colloquially put, the object is to suck him dry.
These are only theories thus far. Observing the mating habits of the Neotrogla in their natural habitat can be arduous. The immediate goal is to have these insects multiply in the entomologist’s lab, so it can be studied further.
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