Poop-Eating Naked Mole Rats Get Suckered Into Babysitting

Megan Murphy, Smithsonian's National Zoo
Megan Murphy, Smithsonian's National Zoo / Megan Murphy, Smithsonian's National Zoo

The animal kingdom is filled with deadbeat dads. Raising kids takes energy, and nature often rewards the father who walks (or hops or swims or flies) away. Fewer and farther between are the animal moms who just can’t be bothered. Most of them leave their young to fend for themselves, but there are some who get other animals to do the child-rearing for them.

Naked mole rat mothers definitely fall into that category. Dominant rats bear pups, then leave the rest to their subordinates. Why would the subordinates agree to this plan? Two Japanese researchers have a theory: Pregnancy hormones in the mother’s poop trick the other rats into feeling maternal.

Like ants and bees, naked mole rats follow a eusocial colony structure. That means that there’s one queen rat, a few virile males, and a whole bunch of female workers. The queen’s job is to make babies; the male rats help make babies; and the worker rats do absolutely everything else. This includes digging tunnels, keeping the chambers clean, and defending the colony. It also means raising a whole lot of rat babies.

There’s something else you should know about naked mole rats: they eat poop. The rats’ favorite foods are roots and plant bulbs, which can be pretty hard to digest—so the rats chow down twice. They eat, pass their meal, then eat it again. But they don’t just eat their own poop. The rats use specialized bathroom chambers, which means that their recycled food could have come from anyone—including the queen.

Worker rats don’t have mature sex organs of their own, which means they don’t make sex hormones. But when the queen is knocked up, her poop is positively packed with estrogen. As reported this week in Nature News, researchers from Japan's Azabu University recently presented research findings at the Society for Neuroscience meeting in Chicago that suggest the queen’s hormones inspire maternal impulses in her subordinates. 

First, the scientists played a recording of crying rat pups for a group of subordinate female rats. The worker rats whose queen had just given birth were very interested in the pups’ cries. The other workers were not.

The next step was finding out how the queen rat’s poop affected her workers. The researchers gave subordinate rats hormones from their pregnant queen’s feces. Sure enough, the worker rats’ estrogen levels increased, as did their interest in the sound of crying rat babies.

NOTE: Naked mole rats are not moles, or rats, or even naked, but that’s a story for another day.