Animal Behavior / Biology / Ecology / evolution / gender

Dominant Females and Weird Animal Sex: A look at anglerfish, spotted hyenas, and gender roles

Written by: Julia Zeh

Edited by: Olivia Ghosh

The animal kingdom is chock-full of weird, crazy, mixed-up gender roles and sexualities. From sex-changing fish to homosexual birds, and everything in between, evolution has created an immense diversity among animals when it comes to the behavioral and morphological aspects of gender and sex.

The spotted hyena is an animal lacking a trait that belongs to most other mammals: sexual dimorphism, which is the difference between the ways males and females look and act. The males and females of this hyena species, the largest of three species, look so similar that even trained scientists have a lot trouble telling them apart in the wild. For centuries, people even believed that this was a hermaphroditic species of hyena. However, this species of large, brown, furry scavengers does in fact have both sexes, but they are easily mistaken for one another because the two sexes have almost identical genitalia. That’s right, the females of these animals, well known for their eerie laugh and their appearance in a well-known Disney movie about lions, do in fact have what is known as a “pseudopenis.”

spotted hyena (Crocuta crocuta), welcoming each other, Kenya, Amboseli National Park

A male and female hyena engage in greeting behaviors by sniffing each other.

Another interesting thing about this species is their complex social structure, dominated by aggressive females who also tend to be larger than the males. The weird anatomy of the females is a Darwinian puzzle, or an evolutionary mystery, thanks to the danger to hyena offspring that comes from the existence of the pseudopenis. These females urinate, copulate, and give birth with this organ. Yes, the cringe worthy truth is that these hyena moms give birth through the pseudopenis, which results in a 60% death rate of first-born cubs and 10% death rate of new moms. So if this experience, which not only sounds painful, is also detrimental to the health of offspring, why hasn’t natural selection gotten rid of it?

The answer lies in the complex social structure of the species. Determining a social hierarchy is vital to the way the social structures of these hyenas works, and that’s why these pseudopenises exist. As a greeting ceremony, individuals sniff each other’s genitals, and this greeting allows them to determine superiority and dominance. In a species in which females are incredibly aggressive towards both each other and towards males, it is actually an evolutionary advantage to have this structure, despite its costs in reproduction. Females are so aggressive that it is actually dangerous for males to try and mate with them. Males are incredibly submissive and must be very careful around females, especially when trying to mate, so that they are not attacked or even killed. All of this aggression and social hierarchy is important because these hyenas live where food is very scarce. More dominant females are allowed to stay with the clan, and higher ranking females have larger pseudopenises, higher survival rate, and greater access to food.

Outside of the world of mammals lies another well-known group of animals, which, unlike the spotted hyenas, have extreme sexual dimorphism. But like the hyenas, this group has socially dominant females. This animal is the anglerfish, the epitome of alien deep-sea fish known for its bioluminescent, glowing lure that hangs from the top of its head. These fish look terrifying with their large jaws filled with huge teeth that can be used to swallow prey twice their size. But what most people don’t know is that the image that comes to mind when you think “anglerfish” or even the one that comes up when you google it is actually the female, and the male looks drastically different.

57693003_anglerfish

The tiny, parasitic male anglerfish.

Females are, in fact, the only anglerfish with a lure on top of their head and giant jaws and teeth. Males are tiny and lack all of the monster-movie features that the females possess. It would even be easy to call these little guys pathetic, given their life history as parasites of the females. When the male anglerfish is born, in most species, he cannot provide for himself at all and is immediately hungry. But without the ability to eat or catch food, he is totally helpless. The one skill he does possess is a highly specialized sense of smell that he uses to search out his one purpose in life: the female anglerfish. He uses smell to seek out his larger, scarier counterpart, eventually biting into her side in an attempt to finally provide himself with a form of nutrition. But even after finding food and a female, the little guy doesn’t get a happy ending.

The male anglerfish fuses with the female after he bites into her, and this is how reproduction occurs. Eventually, all of his internal organs and eyes atrophy and dissolve until he becomes merely a pair of testes attached to the female’s side. His body becomes one with hers and he shares her bloodstream, becoming even more helpless than he was at birth, if what he becomes can even be considered existence. Even weirder, the females can have six or more males attached to her body. Like the female hyenas, these females are large and dominant, while the males are smaller, submissive, and in the case of the anglerfish, even helpless. But this is not to say that this more masculine version of the female is the “correct gender role.” Just as with humans, spotted hyenas and anglerfish illustrate how individuals cannot be put into categories and labeled. In the animal kingdom, gender roles are not easily defined, especially considering hermaphrodites and sex-changing individuals exist. What is natural is weird and varying and even in the animal kingdom, outside of the realm of the human, there is no universal definition of male and female.

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