Studies Of Hyena Skull Development Put Teeth Into New Female Dominance Theory

Females rule among spotted hyenas, making them rare among mammals and unique among carnivores, Michigan State University researcher Kay Holekamp said. After more than 20 years of closely studying generations of the ferocious, yet social creatures, Holekamp and colleagues now believe they know why.

"We've been unhappy with previous explanations of sex role reversal in hyenas for some time," said zoology professor Holekamp, who is recognized as a top authority on the spotted hyena.

Holekamp and associates theorize that the length of time it takes for the massive skulls and jaws of hyenas to mature in youngsters – combined with the intense feeding competition typical of hyena clans – prompt female family members to develop dominant behaviors. "Mothers have to compensate with aggression for the handicaps their kids are experiencing during feeding," she said.

Hyena cubs are at particular risk after they are weaned, she said, because their skulls don't fully develop until after sexual maturity.

More closely related to cats than dogs, hyenas are most closely related to the animal family that includes mongooses. They can weigh up to 185 pounds and stand up to 3 feet tall, with jaws capable of cracking open giraffe leg bones up to 3 inches in diameter. Known mostly as scavengers and able to eat things that would sicken or kill many other species, they also are good hunters, capable of bringing down prey several times their own size.

The complex social system established by spotted hyenas, which live in clans numbering up to 90 members, is a prime area of research in Holekamp's lab.

Holekamp was joined in her research by Heather Watts, the report's lead author, and Jaime Tanner, both former Holekamp laboratory graduate students. Associate zoology professor Barbara Lundrigan, curator of mammalology and ornithology at the MSU Museum, lent her expertise on skull development and helped develop and test the group’s new hypothesis using many of the museum's 70-plus known-age hyena skulls.

A report describing the researchers' theory is published in the March 18 issue of the Proceedings of the Royal Society B.