Sunday, November 23, 2008

What a difference a nipple makes

We've mentioned several times that sibling rivalry in spotted hyenas is fierce. You might recall from my long-ago post on the dominance hierarchy that if a female has two cubs, one becomes dominant almost immediately, and reaps the benefits of this. It has easier access to the mother's milk, gets cuddled while nursing, and develops faster. In fact, we think that one of our older females, Moon Pie, actually has a bum nipple—all females have two teats—so in this case the difference is especially drastic. When Moon Pie has twins, the dominant cub tends to develop at a much faster rate than its subordinate sibling.

Anyway, here are a couple photos that highlight some of these differences. Remember Falafel, who had newborns back at the end of July? (She was the one who drooled all over one of them.) Here's a chance for you to check in on the progress of her cubs, Tilt and Jordache. It is difficult to see the difference in size because they aren't in the same photo, but you are able to see the difference in development. Notice how Tilt, the dominant cub (top photo), is already getting its spots, whereas Jordache, the subordinate cub (bottom photo), is still mostly black:

But it gets better. Perhaps you also recall that there's not only a difference between dominant and subordinate siblings...there's also a difference between high-ranking and low-ranking cubs. High-ranking cubs develop much more quickly than their low-ranking counterparts, because their moms have better access to food. Here's a picture of two cubs, Jordache (left) and Monopoly (right), that were born within two days of one another, and look at the tremendous size difference between them:

Monopoly is the granddaughter of Murphy, our alpha female, whereas Jordache is the granddaughter of a low-ranking female in a different matriline. You can see we're not messing around when we say this whole rank thing is pretty important. The last photo is also of Monopoly, and I'm including it just to give you a better idea of how quickly Monopoly's spots have come in compared to those of Tilt or Jordache.


Anonymous said...

Nature is indeed brutally unfair.

It makes me all the more curious what the evolutionary reasons are behind such intense sibling rivalry in spotted hyenas. I know research on this hasn't been very enlightening so far, but hopefully it will continue.

Leslie said...

Well, it certainly doesn't help that these "twins" might not have the same baby-daddies. Hyena females are what evolutionary biologists so delicately refer to as "promiscuous" (I'll let you choose your own word for it), so it's quite common for littermates to have been sired by different males. So these kids might very well only be half-siblings.

Anonymous said...

Thank you for the response. I imagine it doesn't help! But . . . surely there are other mammals with promiscuous females who give birth to multiple offspring? And the only other animals I can think of with such vicious sibling rivalry -- raptor birds, to which I've seen spotted hyenas compared -- tend to live in monogamous mated pairs for the most part.

Anonymous said...

With domestic cats, you can have kittens in the same litter sired by different males, but I can't speak to the level of sibling rivalry.

Jaime said...

Tilt and Jordache look just like Falafel did when she was a cub!! so cute

Jaime said...

Jordache and Tilt look just like Falafel did when she was a cub! So Cute!

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