October 10, 2013
For meerkats, survival depends on the group. These adorable small mammals live in communities of up to 50 in southern Africa and help each other out by keeping a watchful collective eye out for the numerous taloned, clawed and fanged predators that would delight in a meerkat dinner.
But meerkat society is no democracy. Here, a dominant female and male reign supreme, dictating the jobs and reproductive rights of all subordinate members in what researchers aptly refer to as the meerkat “mob” or “gang.” When lower level females do manage to birth their own litter of pups, retaliation is swift and brutal. Alpha females kill those unwelcome, helpless additions to the colony, and, according to new research, then present the bereaved mothers with two options: leave the colony, or earn their keep as wet-nurses for the offspring of their babies’ killer.
Scientists refer to such wet-nursing in the animal kingdom as allolactation. Usually, allolactation is a peaceful, communal affair, occurring when several females breed in unison and share responsibilities for taking care of one another’s young. In some cases, however–such as with the meerkats–only a single female will breed but will coerce others to share or even accept the full burden of her pup-rearing duties. In the meerkats’ case, other females babysit the alpha pair’s pups and even risk their lives protecting the young, for example, by throwing themselves over the babies as a living shield if a predator comes near.
Obviously, tending to another meerkat’s offspring–which may have no genetic relation to the caretaker–is costly. Females enlisted to help often lose significant amounts of weight in the process.
Researchers from the United Kingdom and South Africa wanted to better understand what circumstances dictate whether a female will fall victim to this perplexing form of servitude, and why. To find out, they spent 15 years observing meerkats from 40 different social groups at a nature reserve in South Africa. They collected information such as who the dominant female was, which females got pregnant, which successfully birthed and raised young, which continued to lactate while pups were around and how much both the females and the pups weighed throughout the whole process. They assembled what they think is the most comprehensive long-term data set on this subject to date and published their results in the journal Animal Behaviour.
The subordinate females, their data showed, were most likely to pitch in with nursing or other forms of child-tending if their pups had been killed by the alpha female, or if they had been evicted from the colony but had come slinking back in the hopes of regaining a place there. In other words, the authors write in a release, taking care of the dominant female’s babies was a form of punishment or even “rent” to be paid for bad behavior.
“Infanticide by the dominant female might have two evolutionary advantages for her–she reduces competition for care for her own pups, and is more likely to secure allolactation for her litter,” explains Kirsty MacLeod, a zoologist at the University of Cambridge and co-author of the study.
So what’s in it for the poor, abused underling females? The researchers are still teasing out those perplexities, but they think that the stress and danger of living alone as a single female may outweigh the annoyance of having to care for the dominant female’s young, since that duty at least entitles the caretaker to enjoying the relative safety afforded by the colony. Those who are kicked out of the colony, the researchers observed, suffered higher mortality rates than those who remained or returned there.
“If contributing to the maternal cares of another’s offspring allowed renewed access to the social group, or to remain in the group once following infanticide, there would be an incentive to ‘pay-to-stay,’” MacLeod says. In some cases, the team adds, caretakers may be genetically related–either loosely or directly–to the pups, providing another incentive for ensuring those little ones survive.
For a few rogue females, however, eviction from the colony winds up working in their favor. New meerkat mobs are formed when lone females run into stray males and create their own social groups from scratch. But rather than break the cycle of abuse that landed her in that position to begin with, those newly dominant females likewise relish in the power afforded by their queenly standing. They, too, will happily dish out a serving of infanticide and enslavement to any females that cross them.
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