Saturday, October 18, 2014

Female Chimps and Male Attention

Everything is connected. More time spent resting means less time spent grooming. Less time spent grooming may mean greater chance of parasites and thus a greater chance of illness. Illness means greater chance of mortality. This is just one example of how everything is connected and one aspect of life affects another. The same is true whether one is a chimpanzee or a human. If you spend more time playing soccer with your friends, you will need to spend less time doing your homework. Or maybe you will compensate for that time lost doing your homework by working late into the night and sleeping less.

Chimps grooming, Photo credit flickr user Tambako the Tiger
One would think that receiving male attention would be a good thing, if one is a female chimpanzee. The more males seeking your attention, the more choice you have, right? The more opportunities to mate, and since an individual's fitness is a measure of the number of offspring one produces that survive to maturity, mating is an important part of life. So it's straightforward then. The more male attention, the better. Right? Not so fast...

A recent study led by Melissa Emery Thompson of the University of New Mexico found that male attention comes with costs. In the world of chimpanzees, males do indeed compete to mate with females. (Chimpanzees live in groups of multiple males and females and males are dominant over females.) A female will give birth to an offspring and then raise that offspring for five to seven years, which is a pretty long time in the animal kingdom. In part because female chimps raise their young for so long, males compete seriously for access to females. It's not as though the guys always have a chance with that type of reproductive schedule. Females will mate with multiple males, some of whom will then guard her to prevent other males from mating with her, so she can receive quite a bit of attention, whether she wants it or not.

For eleven years, researchers observed chimpanzee behavior and collected their urine to analyze or study hormones (naturally occurring substances that affect or regulate the activity of other cells or organs), such as estrogen and progesterone, which are two female sex hormones important for female sex characteristics and for reproduction. Emery Thompson and colleagues also collected urine to look for C-peptides, a byproduct of insulin. Declining levels of C-peptides indicate a female is spending more energy than she is currently consuming, which is not good.

Chimpanzees with offspring, Photo credit: flickr user Valerie
What they found was that females with more males surrounding them had lower levels of C-peptides and lower levels of those reproductive hormones. Thus, females with all of this attention are not consuming enough energy and are producing fewer hormones than needed. It appears that all of this male attention could very well stress out the females. Perhaps all of that attention from males means that females are less efficient at foraging and obtaining the food they need. Or perhaps they feel a need to keep an eye on those males, as males are dominant, and this extra vigilance is taxing or stressing. Whatever the exact connection is, it appears there are costs to having a lot of males around when cycling or lactating.

Food for thought: Why might female chimpanzees mate with multiple males? Hint: do some research into infanticide and think about how this might protect against it.

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