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Mating Games at Meerkat Manor
22 September 2010 4:07 pm
Fans of the Animal Planet show Meerkat Manor, which follows the lives of a group of African meerkats, are familiar with the drama: The dominant female that rules the group keeps subordinate females from reproducing by kicking them out. Sometimes they come back, and sometimes they start a new group. A new study of the animals, including the stars of the show, finds that dominant females may decide when to suppress their subordinates' reproduction based on the costs and benefits to themselves.
Meerkats live in tight family groups in the Kalahari Desert of South Africa and Botswana. The meerkats on Meerkat Manor are part of a study that started in 1993 and has followed roughly 3000 animals through their lives. The animals live in groups that range around the desert. Every morning when they wake up, and twice later in the day, they've been trained to step onto a set of scales to be weighed. The animals have generated reams of data in the past 17 years.
In meerkat groups, one female is generally in charge, giving birth to most of the pups and thereby passing the most genes on to the next generation. She may keep the other females from reproducing by evicting them, either temporarily or permanently, or by killing their pups. But sometimes, other females in the group manage to have offspring. Researchers have debated the question of why dominants sometimes let subordinates breed—in meerkats and in other species—for years, says Tim Clutton-Brock, a behavioral ecologist at the University of Cambridge in the United Kingdom. One theory says that dominants are trading with subordinates, letting them have some of their own babies in exchange for sticking around to help. Another theory holds that subordinates manage to reproduce when dominants aren't strong enough to stop them.
But Clutton-Brock says these theories leave out another consideration: in meerkats and in many other cooperatively breeding animals, the members of the group are usually related. So it's not a total loss for the dominant when one of her sisters, daughters, or nieces reproduces, because some of her genes are passed on to their offspring. He has an alternative suggestion: A dominant either suppresses her subordinates or eases up depending on the costs and benefits to herself.
Clutton-Brock and his colleagues looked for patterns when females suppressed subordinates' reproduction and when they didn't. They found that a dominant was more likely to suppress another female if she herself was pregnant. But if she had already given birth and was nursing, she was less likely to do so. "So that would be a case which is most easily explained by the theory that we are suggesting," says Clutton-Brock. In this case, if the dominant and subordinate are pregnant at the same time, their pups will compete for resources. But if the subordinate's pups are born later, they aren't as much of a threat, says Clutton-Brock. So suppressing them might not be worth the energy for the dominant. Clutton-Brock and colleagues reported the findings online 16 September in The American Naturalist.
The paper provides useful real-world data on a question that's gotten a lot of theoretical attention in the past couple of decades, says Hudson Kern Reeve, an evolutionary biologist at Cornell University who was not involved in the study. "We're very theory-rich right now, but we're lacking details" on how animals actually spread reproduction around. Evolutionary biologists hope to eventually come up with a theory that explains how all animal societies are put together—including our own.