Spotted hyena females have a pseudopenis, or penile-clitoris. This makes it nearly impossible to differentiate between the sexes. It’s even possible for females to achieve erections. Their external labia are fused together and form a pseudoscrotum.
As you can imagine, the act of copulation is not simple. The female must first retract her penile-clitoris into her own body. Think about turning a sock inside out. The male can only insert his penis once the female has tucked her pseudopenis inside her body.
How Does The Female Spotted Hyena Give Birth?The genital structures of the female spotted hyenas win them the distinction of being the only mammalian females to copulate, urinate, and give birth through the penile-like canal. Click To Tweet
The female gestates offspring in her uterus, but also gives birth through the penile-clitoris. The birth canal is approximately 2.5cm in diameter. Females often experience severe tearing. The rate of female mortality during childbirth is abnormally high for first-time mothers. The babies can separate from the placenta, get caught in the birth canal, and die.
Why Would a Female Spotted Hyena Have a Penis?
There are a few schools of thought with respect to the evolutionary origins of the penile-clitoris:
- the submission signal hypothesis suggests that the structure evolved at least partly in a social context
- the nonadaptive hypothesis suggests that the extremely masculinized genitalia of these ladies is an evolutionary by-product resulting from possession of androgens and testosterone
- the sexual mimicry hypothesis suggests that the pressure for females to appear as males is greatest at early stages of a female’s life
The submission signal hypothesis
High-ranking spotted hyena females are extremely aggressive towards both males and lower-ranking females. They realize a higher level of nutrition and reproductive success than subordinates. They may attack lower-ranking females and their offspring.
Existence of a ritualistic behaviour that reiterates social status may be advantageous for high- and low-ranking females. When females greet each other, they stand in a parallel position, facing in opposite directions. They then lift their hind legs and display their fully erect penises to each other. They will lick and smell each other’s penises.
The more submissive individual will perform a suite of behaviours. This could represent some kind of mutual communication about social status. It would make sense for a low-ranking female to engage in whatever submissive postures she can because this position leaves her most delicate bits completely vulnerable.
The nonadaptive hypothesis
Female spotted hyenas have androgens (hormones) in their systems. These substances are associated with dominance and social status. Testosterone levels in spotted hyena females are as high as those in males. It’s thought that high levels of testosterone are transferred to male and female offspring through the placenta. This exposes both sexes to a high level of maleness during gestation.
These steroids in adult females make them extremely aggressive, much more so than their male counterparts, despite being of similar physical size.
The feeding system of spotted hyenas illustrates a clear advantage for females to be dominant. Spotted hyenas converge on freshly killed prey and eat as a group. Over twenty individuals may be vying for a piece of a kill, so competition is high. A group of spotted hyenas can transform a wildebeest to mere stains on the grass in a matter of minutes. High-ranking females are the first to indulge in a kill, along with their offspring. Low-ranking females and their offspring are next on the list, finally followed by adult males.
Without question, females are socially dominant to males. There are clear ecological advantages to having high levels of androgens and testosterone. The extremely masculinized genitalia of spotted hyena female could simply be an evolutionary by-product.
The sexual mimicry hypothesis
A third hypothesis for the evolution of the penile-clitoris has to do with the notion of sexual monomorphism. Sexual monomorphism is when both sexes look the same. It’s thought that sexual monomorphism in spotted hyenas could be advantageous for a few reasons:
- There is intense aggression between newborn hyenas. They are located in underground dens that are not easily reached by their mother or any other adult. They have functional incisors, large canines and muscular necks and jaws. In addition, they are extremely aggressive, often attacking anything that moves. Female newborns experience a greater level of siblicide than males. Males have the lowest rank, so a male newborn is a much lesser threat than a female.
- High-ranking females have been observed to kill the female offspring of lower-ranking females. This substantiates a biological desire to keep the pool of competitors low.
When spotted hyena pups are born, they are virtually identical. They can only be sexed through molecular means; male and female genitalia are indistinguishable. The physical resemblance between males and females decreases from infancy onwards. This suggests that the pressure for females to appear as males is the greatest at the early stages of a female spotted hyena’s life.The female spotted hyena's pseudopenis or penile-clitoris has both immense benefits, such as social dominance and sexual dominance, as well as immense costs, like having to give birth through a penis. Click To Tweet
This post is an excerpt from my book “Wild Sex: The Science Behind Mating in the Animal Kingdom“
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