Female insects of the troglodyte genus Neotrogla having penises – until now, so commonplace. A study has now revealed that the muscles they use to protrude and retract their limbs evolved before the sex roles of these creatures were reversed, and that their previous function may have been to provide females with a tasty snack in the morning. middle of sex.
It was in 2014 that a group of Japanese researchers reported something unusual about Neotrogla. There are four species in this genus, and all have inverted genitals – males have a structure that resembles a vagina, while females have the equivalent of a penis, called a gynosome. It seems that they put these organs to good use, passing the time in the Brazilian caves they inhabit with copulation sessions that can last between 40 and 70 hours. That’s right, hours.
Previous research has been able to speculate as to why Neotrogla evolved to mate this way. It is important to note that despite their anatomical differences, the males of the species still produce sperm, while the females produce eggs. It is believed that the arid environment they inhabit meant that Neotrogla females were to become more efficient sperm collectors, evolving the gynosome as a mechanism to collect as much sperm – from as many males – as possible.
What was not well understood, until now, was how females manage the protrusion and retraction of their appendages.
A new study by a group of researchers from Japan, Brazil and Switzerland has found an answer. The team used a 3D X-ray technique called micro-tomography (µCT) to compare the anatomy of Neotrogla with other closely related insects. The µCT data confirmed that the female Neotrogla had developed two specific groups of muscles to enable them to expand the gynosome, in order to enter the vagina-like male genitalia.
However, these same muscles have also been found in related insects that lacked fully functioning penises. This led researchers to conclude that these muscles must have evolved before sex roles in Neotrogla were traded – the question is, why?
It is likely that the muscles could be used by females, in the absence of a gynosome, to stimulate male insects during sex to promote the release of more sperm. As it happens, Neotrogla sperm is more than just a means of reproduction – it is also a very nutritious snack for the hungry female. Since their main diet is dead bats and their droppings, you can’t really blame them for wanting a bit of a change.
As the study authors say, the evolution of these muscles was likely the key to the sex-role reversal that makes these little wrens so fascinating: “This intermediate stage likely allowed for the reversal of genital functions.
The study is published in the Royal Society Open Science.