Published online: 8 August 2006; | doi:10.1038/news060807-4
Cute meerkats actually vicious baby killersCooperative society gets stressed out when babies are involved.
Research shows that although meerkat societies are generally cooperative, when it comes to pregnant females all bets are off. If a meerkat gets pregnant, she will actively try to kill the pups of other females. And now it seems that the most dominant female in the group has an extra strategy for ensuring her pups' survival: she chases and persecutes her potential baby-making competitors until they become so stressed that their fertility collapses1. Meerkats are often held up as examples of a cooperative society. The larger dominant female in a meerkat group usually succeeds in getting pregnant and has most of the babies. When this happens, the other subordinate workers pitch in with the babysitting and pup-feeding. The system is rather like that of the queen bee and worker bees in a hive. Such a hierarchy isn't unusual: other species practicing similar cooperative living include marmoset monkeys, naked mole-rats and acorn woodpeckers. A group of meerkats will run sentry duty for each other, and recent research suggests that they teach the young how to handle dangerous food2.
Young and his colleagues have now shown just how hard the dominant meerkat female fights to win her reproductive success: she chases and attacks subordinate females when she becomes pregnant, driving them away for up to 3 weeks before her own pups are born. "It's a period of really chronic persecution," says Young. Breach of contract The team also found that this has a profound effect on the pursued females. Their glucocorticoid hormones - a sign of stress - shoot up when under attack, reducing their chance of getting pregnant. "The subordinate females' reproductive function collapses," says Young. The team reports the results in the Proceedings of the National Academy of Sciences. This confers multiple advantages on the dominant female. Her pups get all the subsequent baby care to themselves. And it reduces the chance that a jealous subordinate female, pregnant with her own pups, will come after her children with murderous intentions. Pregnant females killing one another's offspring is not unheard of in the animal world — not even in cooperative societies where subordinate females should kowtow to dominant ones, says Wendy Saltzman of the University of California, Davis. But, she says, it is unusual that the dominant mother should have to fight for her position by causing stress in the subordinate females. "There's normally a well-respected social contract in cooperative breeders: subordinate females are tolerated, but don't breed. They seem to have self-restraint," Saltzman says. "This study is the first good evidence that a cooperatively breeding species uses aggression-induced stress to actively stop subordinate females from breeding." The kat walks alone What it all amounts to, says Young, is an interesting clash between selfishness and cooperation. There is a vicious power struggle between dominants and subordinates to see who manages to breed — which the dominant female usually wins. But after that, the cooperative behaviour kicks in and everyone helps to rear the young. "In the long run, it's all genetically selfish," Young comments. "The subordinates attempt to reproduce; if they can't, they try to ensure the survival of the group — on which their own survival depends — and rear their close relatives, who share their genes." So, like politicians, meerkats work for the good of the party, but are vicious back-stabbers when they get the chance.
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When it comes to who should produce the babies, conflict is rife. 