The discovery shows that the sex lives of snakes may be more complicated than previously thought.
A new study has shown that female snakes also have clitoris.
Research raises the possibility that that the sexual life of snakes is more complex and diverse than previously thought, researchers report on December 14 in Proceedings of the Royal Society B.
Clitoris are found in many vertebrates, from crocodiles to dolphins. The exception is birds that have lost their clitoris in the process of evolution. Female snakes also seem to have lost their genitalia, which was surprising because their close lizard relatives have paired clitoris, called hemiclitors. Male lizards and snakes have accompanying paired phalluses, or hemipenis.
This element of the female snake’s sexual anatomy has remained unstudied in detail for so long because the hemiclitoria can be fragile and easily seen, and because female genitalia have historically been considered “quite taboo,” says evolutionary biologist Megan Falwell of the University of Adelaide. in Australia.
“In 2006, the proper function and significance of the human clitoris, even in humans, was still being debated,” she says.
The conflicting information about the snake’s hemiclitoria in some scientific works prompted Falwell to consider them in detail. She first examined a euthanized female common dead viper ( Acanthophis antarcticus ). “I just started by dissecting the tail and going into it with a really open mind to what I might find,” she says.
She was “pleasantly surprised” to find inside the double organs, which were completely different from the hemipenis that male snakes have. Also, unlike the hemiclitors of lizards, snakes could not turn outward.
To confirm that she wasn’t looking at a piece of other tissue, Falwell and her colleagues carefully examined parts of the organs under a microscope. The team also soaked the tail with iodine, which allowed the soft tissue in the genital area to be seen at a higher resolution using X-rays.
These analyzes showed that the tissues are radically different from the hemipenis of male snakes. Female organs were filled mostly with collagen rather than muscle fibers running through the structure. Another analysis showed that the organs have “bunches of nerves,” Falwell says, suggesting they likely have significant tactile sensitivity. Like the clitoris of other species, the clitoris of snakes exhibited a strong blood supply.
The team expanded their study to eight more species of snakes in four families, revealing a dizzying variety of clitoris. For example, according to Falwell, the hemiclitors of the Mexican viper ( Agkistrodon bilineatus ) are huge, filling the tail space. “Then you see Ingram’s brown snake, which was so tiny. If you didn’t know what you were looking for, you could definitely miss it,” Falwell says.
Some hemiclitors are thin and lie on top of the scent glands, while others are sandwiched between them or even combined on top and between them, she adds.
Snakes are believed to be descended from lizard ancestors. The findings show that, from an evolutionary perspective, the snake’s clitoris “was not lost; it was just changed,” says Diane Kelly, an evolutionary biologist at the University of Massachusetts Amherst, who was not involved in the study.
Falwell and her colleagues believe that hemiclitors may be stimulated during courtship and mating behaviors, such as tail curling. This can make the female more receptive, promoting longer and more frequent mating and increasing the chances of fertilization.
“It’s often been thought that in snakes it’s all about coercion and the male inducing mating,” Falwell says. “In some species, it might be a little closer to temptation.”
Looking ahead, Falwell wants to further study how hemiclitor nerves are involved in any touch sensitivity and function during mating.
Kelly notes that comparing the hemipenis and hemiclitoris of the same species can help gain insight into organ function in snakes and potentially reveal any reverse evolution between males and females.
“It’s 2023, and here’s a brand new anatomical discovery in a really common animal,” Kelly says. “There’s a lot of anatomy we don’t know about yet.”
