Some mole-rats lead an easy life. They reap the benefits of constant protection, a steady supply of food to fatten them up, and plenty of sleep since they rarely have to lift a paw.
This type of behavior would seemingly hurt an otherwise busy colony, so scientists have wondered why it is so pervasive.
A new study suggests the laidback lifestyle of some in a colony actually helps the queen mole-rat spread her genes.
How it works
Furry mole-rats, the subject of the new study, are related to the naked variety. A colony consists of one reproductive queen and two siring males. This is an example of a eusocial society, where worker individuals put off reproducing for the good of the colony.
Eusocial colonies are common among insects, but the only examples in the mammal world are the furry and the naked mole-rats. Besides the queen and sires, the rest of the colony is split between two groups of workers. Some 40 percent are loafers. The rest do about 95 percent of the work.
Burrowing in the dry, hard soil of the Kalahari Desert is tough work, so the lazy group spends this time eating and sleeping. But when the rainy season softens the soil, the fat layabouts exert about 40 percent more energy digging than their industrious kin.
"It is after these rare rain events—perhaps once or twice a year—that infrequent workers suddenly 'spring into action' and start digging," said study co-author Michael Scantlebury of the University of Pretoria in South Africa.
The sudden burst of activity isn't meant to better the colony's tunnel system. It's an attempt to escape.
I'm outta here!
Driven by a mole-rat rule that forbids incest, both males and females break from the colony in an effort to pair up with unrelated mole-rats or start new colonies, where they become the breeding leaders. Sometimes males wander from colony to colony, casually reproducing.
Unsuccessful escapees are eaten by snakes.
"We think that infrequent workers fatten themselves up in preparation for meeting the costs of dispersal," Scantlebury told LiveScience. "They may face an extended period of time without food, and perhaps without finding a colony to integrate into, or a new place to found a colony, the fat stores will be very useful."
There's benefit to all this. The researchers believe that by pouring resources into dispersing individuals, the queen and her colony ensure long-term survival and the spread of their genetic information.
The study is detailed in the April 6 issue of the journal Nature.
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