Eating queen’s poop makes naked mole rats babysit her kids

The scat contains a hormone that transforms other females into nannies

As in a honeybee hive, the queen in a naked mole rat colony is the only mom. She gives birth to all of the young. But she’ll need child-care help for all her babies. And she’ll get it from the other females, especially if they’ve dined on her poop, new data show.

Kevin McGee/Flickr (CC BY-NC-SA 2.0)

Dealing with poop is a major part of raising children, regardless of the species. But it’s especially important for naked mole rats. A mom’s poop actually encourages other females in her colony to help with her child care, new data indicate.

Naked mole rats are small, nearly hairless rodents native to East Africa. They live in large underground colonies. A single queen in each colony gives birth to a few dozen pups each year. But she doesn’t care for those babies alone. Other females help her out. These nannies get their cues on when they’re needed from their diet — the queen’s poop. That’s the finding of a new study.

Many females share a colony. Only one of them — the queen — reproduces. Ovaries, a reproductive organ, never develop in the other females. So they can’t bear young. Their job, most of the time, is to find food and defend the colony. But when a queen becomes a mom, those other females assume an additional role: babysitter. They groom the babies and keep them warm. They also respond to crying and make sure the pups stay in the nest.

In other animals, hormone changes during pregnancy usually serve as cues for such nurturing. Except for their queen, female naked mole rats don’t experience those changes. Yet they still care for her babies.

Kazutaka Mogi works at Azabu University in Sagamihara, Japan. This developmental biologist was part of a team that explored what might cause these females to become her brood’s babysitters. They focused on one of this species’ most unusual foods: dung.

Feces contain partially digested food. That’s why naked mole rats regularly eat each other’s poop. It allows these rodents to extract additional nutrients initially left behind in the wastes. The feces of a pregnant queen contain high levels of one female sex hormone — estradiol (Ess-truh-DY-awl).

Mogi’s group looked to see if it was what made the other females act like moms.

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The poop of a queen naked mole rat contains the hormone estradiol. Eating poop laced with that hormone appears to encourage other females to care for her young.
Ltshears/Wikimedia Commons

They started by collecting poop pellets from nonpregnant queens. They added estradiol to half of the pellets. This would mimic those shed by pregnant mole rats. Then the scientists fed plain and hormone-treated pellets to female mole rats for nine days.

Those eating the treated feces excreted more estradiol in their own dung. That showed that dining on the hormone-packed poop can change her own hormone levels. And mole rats that had done this were more responsive to a pup’s cries than were females that ate poop without the hormone boost.

Mogi studies how animals change and grow at different stages of their lives. The queen’s poop may not be directly shared with the whole colony, he says. Instead, those that spend the most time in her nest are probably the ones that eat her scat. They may, in turn, pass estradiol down to other colony members through their own poop, he says.

His team shared its findings August 27 in the Proceedings of the National Academy of Sciences.

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