Speaker is Kay Holekamp, professor of zoology discussing how skull development of hyena cubs affects the female-dominated social order of the spotted hyena:
I think what we’ve done here that’s novel is make it clear that the patterns of development in an offspring have a big effect on the evolution of the parent’s behavior.
Sexual reversed dominance in spotted hyenas sets the stage for us to inquire about constraints on the development of the offspring. The adult hyena can actually break through a bone the size of my upper arm without any difficulty at all, but a young hyena even well after it’s reproductively mature still can’t feed as quickly as an adult because it takes a long time to develop the skull of a bone-cracking creature.
[Photos of hyenas gnawing on bones and hyena skull comparison of an infant cub to a young adult.]
We do have other bone-cracking hyenas. There are striped hyenas and brown hyenas and they have the same feeding capabilities as spotted hyenas but they don’t actually experience any competition feeding because they don’t live in complex groups like spotted hyenas do. They feed solitarily.
I’m just going to show you some techniques my colleague Barbara Lundrigan, MSU Museum, has been using to study the development of morphology in hyena skulls.
[At her computer, Holekamp demonstrates plotting hyena and coyote skull development on digital graph paper, and how the reference points change over time.]
So what we’ve done here is to place landmarks on specific known points on the skull of an adult hyena and we’ve picked landmarks that one can also identify on the skulls of infant hyenas and what one can do then is take these landmarks, move them over onto effectively a piece of digital graph paper, and you can actually take the size of the skull out of the equation and compare the skull of a neonate, brand-new baby hyena here with the skull of an adult. And then you can actually watch as those landmarks change in space over the course of hyena development, like that.
And if you do the very same thing in an animal that’s not specialized for eating bone like the coyote-- here’s a baby, brand-new newborn coyote and an adult coyote, and you can see the extent of the morphological change is much less. The upshot of all this is that the coyote development is finished by the time they’re about five and a half or six months of age – this is work by one of my other graduate students, Suzanne LaCroix, by the way – and the hyena development changes in skull shape continues well after puberty.
[Photos of a hyena clan feeding in Africa and of a female hyena nursing her young.]
We’ve known for many years that an organism’s state at birth can affect the kind and intensity of parental care that parents are likely to give to their offspring, but for the first time this actually shows that the patterns of post-natal development and in fact post-pubertal development are of tremendous importance. Especially when a creature with the kind of development constraints that we’re seeing in hyena development lives in a complex society where there are other selection pressures acting on it, it’s going to have profound effects on evolutionary behavior.
[Videography and production by Mark Fellows, Department of University Relations]