This story appears in the February 2017 issue of National Geographic magazine.
Imagine a commune where up to 50 individuals cohabit but only two get to have sex. That’s essentially the cooperative breeding system of meerkat groups, in which one dominant male and female monopolize the mating and pup-bearing.
What helps that female keep her coveted position? For one thing, weight gain.
Since founding the Kalahari Meerkat Project in 1993, University of Cambridge professor Tim Clutton-Brock has studied some 100 meerkat groups. By means of age, weight, and aggressiveness, a male and a female become each group’s dominants and breeders. Other members act as sentries, burrowers, and babysitters.
As subordinates mature, males often leave the group. Females can stay, and the oldest and heaviest usually succeeds the dominant at her death. Researchers wondered: If lighter females in that waiting line gained weight, would heavier females also increase their growth to stay ahead?
To test that idea, for weeks researchers fed a boiled egg a day to one set of meerkat females but not their littermates. They trained both sets to climb onto scales, logged their weights—and found that those not fed still gained weight as the others did, by upping their foraging. To researcher Elise Huchard, it shows that meerkats “can track changes in the growth and size of potential competitors, and react by adjusting their own growth.”
Warding off challenges by gaining weight is a relatively benign approach. If subordinate females attempt to breed, dominant ones may harass them until they abort, or kill pups they bear. “If you get to the breeding position, you’ve hit the reproductive jackpot,” Clutton-Brock says. “That’s worth fighting for.”