The Peculiar Reproductive Anatomy of Female Spotted Hyenas

演化之聲
Mar 13
2 min read

Updated: Apr 10

Female spotted hyena（Courtesy of Bettina Wachter）

In hyenas such as the striped hyena (Hyaena hyaena) and the spotted hyena (Crocuta crocuta), females possess structures resembling a penis and scrotum that develop from the clitoris. In striped hyenas this condition is typically temporary, whereas in the spotted hyena it is permanent. In female spotted hyenas, the enlarged clitoris forms a fully developed pseudo-penis that functions in urination, copulation, and parturition.

During mating, the female retracts this pseudo-penis toward the abdomen, creating an opening through which the male can achieve intromission. Because the opening is produced only when the female retracts the clitoris, control of copulation rests largely with the female. If she refuses mating, she simply leaves the pseudo-penis extended, preventing the male from proceeding.

A female usually gives birth to two to four cubs per litter, each weighing about one kilogram. The internal channel of the pseudo-penis is narrow, with an opening roughly 1.5 centimeters in diameter. Cubs must pass through this channel during birth. Although the opening can stretch during parturition, the elongated and constricted structure of the pseudo-penis often causes tearing of the tissue. As a result, deformation or rupture of the clitoris frequently occurs after the first birth. Because the birth canal is so restricted, a considerable proportion of cubs die from suffocation during delivery.

This reproductive mechanism is unique to the spotted hyena. Other hyena species, such as the striped hyena, give birth through a conventional vaginal opening and therefore do not experience these complications.

Penis-like clitoris of a female spotted hyena（Courtesy of Cunha GR et al）

Three main hypotheses have been proposed to explain why female spotted hyenas evolved this unusual anatomy:

Spotted hyenas often display their genital region to one another during social interactions as a signal of social rank, and the penis-like structure may function as a symbol of status within the group.
In spotted hyena societies, females typically hold higher social rank than males and tend to be more aggressive. Females also feed before males at carcasses. This social dominance is associated with elevated testosterone levels in females, and the pseudo-penis may have arisen as a developmental by-product of these hormonal conditions.
The presence of a pseudo-penis makes females resemble males in external appearance, which may contribute to maintaining their dominance over male individuals within the social hierarchy.