Crocuta Crocuta - The Spotted Hyena

Fighting, originally uploaded by laurentrouas.

Spotted hyenas have a reputation for gross behaviour. No surprise since:

• They have a bone crushing bite which helps them to break up the skeletons of their prey, which they eat.

• They are an aggressive species. It is not unusual for new cubs to kill their siblings within hours of birth.

Spotted Hyaena (01129), originally uploaded by giamplume.

However, this isn't quite fair. For one, spotted hyenas are highly intelligent and exhibit a wide array of sophisticated social behaviours including:

• deception
• recognizing trustworthiness
  

Their intelligence and social ability makes them comparable to certain primate groups.

Combat, originally uploaded by laurentrouas.

But Corcuta crocuta is most famous for it's unusual sex role and appearance reversals.

• Women rule. Females are larger and more aggressive. Even the lowest ranked female in the dominance hierarchy comes before the highest ranked male.

• Females have masculinized external genitalia that closely resembles the male genitalia and is capable of producing erections. This structure allows them to choose absolutely who they will and will not mate with. Amazingly, they even deliver young through this pseudopenis.

About that:

Males are less aggressive and more submissive, but in adulthood have higher levels of circulating androgens than female hyenas. Androgens are male hormones that are associated with aggression and dominance behaviour in mammals, including humans.

We don't understand why females develop masculinized genitalia.

Some background: In most mammals (again, including humans) a fetus exposed to high androgen concentrations will develop male reproductive structures. Human women with congenital adrenal hyperplasia may have moderately to severely masculinized genetalia. Alternately, genetic males with faulty androgen receptors (AIS) can develop completely as females.

With this in mind, you might expect that female spotted hyenas are exposed to unusually high concentrations of androgens while in the womb and you would be correct. However, steps taken to block the effects of androgens on the developing fetus have no effect on the development of masculinized genitalia. For scientists, this is quite surprising and weird!

Just sayin' ...

More Please:
The Paradoxical Predator
Who's Laughing Now?
Spotted Hyena @ Wikipedia