Compare the meerkat: Animals size each other up in race to top

Meerkats have a real hunger to succeed. In the race to the top of the breeding group they pig out to boost their own growth in response to a rival gaining weight.

In the strict social hierarchy of meerkats, a dominant pair all but monopolises breeding responsibilities.

Up and comers in both sexes can wait for years for the top spot to free up – and when the time comes, it’s usually the fattest meerkat that wins.

“There is intense selection to get to the breeding position,” says Tim Clutton-Brock at the University of Cambridge.

Relatively few females will get the chance to breed, and the dominant female even kills off any rival offspring until she has had her litter.

“Those that become dominant and keep their rivals down hit the reproductive jackpot,” says Alex Thornton at the University of Exeter, UK.

Previous research had found that when meerkats reach the top spot, there is an increased growth rate for a few months to consolidate their position.

To find out if this also applied to those jostling for position, Clutton-Brock and his colleagues conducted an experiment in 14 breeding groups in the Kalahari Desert. They took 48 pairs of same-sex siblings and bulked up selected lighter siblings with doses of boiled egg.

Over three months, the team measured the growth rates of each individual, compared with a control group feeding naturally.

When faced with a fattening rival, meerkats from both sexes actively increased their own food intake – and subsequent growth rate – to try to stay heavier.

Those meerkats that tried to keep up with the induced growth rate of their rivals gave up half way through, though. This is possibly because they simply couldn’t keep up or because of the dangers involved with extra foraging, such as increased risk of predation.

The team has also extended the previous work, showing that when a meerkat first becomes dominant, it grows bigger if its nearest rival is close to its own weight.

Similar competitive mechanisms may be widespread in the animal kingdom, says Clutton-Brock. “It’s well worth investigating in other species even if it may not be quite as pronounced.”

Could it also apply to humans? Weight isn’t so important in humans, but it isn’t unimportant either, says Clutton-Brock.

In food-limited populations there may well be competition between twins. “It would be interesting to see whether there were faster growth rates in same-sex heterozygotic twins than in mixed twins,” he says.

This paper adds to a growing literature that is “fundamentally changing the way we think about vertebrate growth”, says Peter Buston at Boston University.

“We used to think of growth in vertebrates as a fixed thing,” he says. “But what’s clear is that vertebrate animals are refining their growth, and even using it to compete with each other.”

Journal reference: Nature, DOI: 10.1038/nature17986

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