Friend or foe? Naked mole rats can tell by a unique squeak

When two nearly blind naked mole rats encounter each other in a dark subterranean tunnel, it could be a friendly meeting or a moment of potential bloodshed between strangers. The creatures chirp to each other in greeting—and what happens next depends on the exact sound of those chirps.

That's because each colony of naked mole rats speaks its own distinct dialect, instantly recognizable to its members, according to a new study in the journal Science. Young pups learn their group's dialect as they grow up, and it is part of a strict culture of conformity maintained by the colony's queen.

"We actually think that one of the ways in which the queen maintains her control is to make sure that everyone is rigidly adhering to a certain dialect," says Alison Barker, a scientist at the Max Delbrück Center for Molecular Medicine in Berlin, Germany.

This discovery means that naked mole rats joins a small group of animals—humans, songbirds, whales—known to have linguistic variations that can reveal where they are from. And scientists interested in how language gets learned now have a small mammal that they can use to study this process in a lab.

"I think for me, one of the most fascinating things is that a vocal culture exists in a rodent brain," says Gary Lewin, another member of the research team in Berlin. "When you take that brain out and you look at the brain next to a mouse's brain, you wouldn't be able to tell the difference."

Communicating with dialects is far from the only weird feature of naked mole rats, which have long fascinated biologists. These almost sightless, almost hairless rodents are neither moles nor rats. Normally, dozens of dwell together in complicated burrows underground in arid parts of East Africa, seeking out plant tubers for nourishment.

These creatures are cold-blooded, can survive on little oxygen, seem to resist cancer and certain kinds of pain—plus, they can live for over thirty years, a long, long time for a rodent.

What's more, their societies operate like an ant or bee colony. A dominant queen is the only one who gets to have babies, while everyone else has jobs and works together for the common good. These naked mole rat groups are incredibly xenophobic and will attack outsiders.

Barker wondered if that complex social behavior might somehow be linked to the animals' constant chattering. "They were making all these kind of strange bird-like noises," says Barker, who explains that how naked mole rats communicate hasn't been examined all that much in the past.

So she and her colleagues spent a long time recording and cataloging these animals' vocalizations. "We can say now that there's about 25 different sounds that they make," says Barker.

Her favorite is a rare one known as the "toilet call." The naked mole rats have a communal toilet chamber, says Barker, and the queen sings a little song when she goes in there. "That, for example, is something that we have no idea what it means, but is a really cool direction that we want to look into in the future," says Barker.

What they've looked at already is a far more common communication known as the "soft chirp." It's a basic greeting noise that naked mole rats make all the time.

"So if you were a naked mole rat and you were walking in a tunnel and you bumped into another naked mole rat, which happens quite frequently, you'd both emit your own soft chirp," says Barker.

The research team focused in on this chirp, recording more than 36,000 examples from 166 naked mole rats living in seven colonies--which they named after Game of Thrones groups like Baratheon and Dothraki.

"We put them in a little chamber and we would just record individuals making different soft chirps," says Barker.

An analysis of the the acoustical properties of these chirps, performed using machine learning techniques, revealed that each naked mole rat's group had its own distinctive sound. And when the researchers played soft chirps to naked mole rats in the lab, say Barker, "almost all of the time they only responded when they were presented with a dialect that matched their home colony."

These dialects appear to be learned rather than innate, because very young pups that got adopted into different colonies ended up speaking like the naked mole rats that raised them.

"Of course, it would be exactly the same for humans," says Lewin. "If I'm born in Scotland and I'm moved to, let's say, somewhere in England when I'm two years old, then of course I will probably grow up not Scottish, but speaking the new dialect."

The researchers believe that the queen plays a key role in keeping a colony speaking with one voice. When she dies, explains Lewin, a group will go through a period of relative chaos and infighting, and individuals within a colony start to make soft chirps that sound more variable. That variability goes away once a new queen establishes herself and starts breeding.

The new report on all these findings has thrilled other researchers who study naked mole rats. "I loved it. I really did. And I'm jealous. I wish I had come up with this idea," says Thomas Park of the University of Illinois at Chicago.

He has hundreds of naked mole rats in his lab. "It's a cacophony in there. They're always talking. It's amazing," he says.

"I think having a laboratory animal, a laboratory rodent model of language learning, is going to be really a game changer," says Park, noting that naked mole rats could be used to study language learning problems that affect people, for example.

Rochelle Buffenstein of Calico Life Sciences, who studies aging in naked mole rats and has thousands in her lab, agrees that this is a real opportunity for biological research on language acquisition.

"To me it appears that naked mole rats are clearly able to learn vocalization in much the same way that humans and song birds do, and create this language through vocal mimicry, which is unheard of in other rodents," says Buffenstein.

She had suspected that naked mole rats would recognized intruders based on their smell, not the "foreign" way that an outsider would chirp hello. "I thought that was very fascinating that there was a vocalization component to it," she says.

While Park was somewhat surprised to learn about these animals' culturally-specific way of communicating, another part of him wasn't surprised at all.

"When you think about all the other really cool things about naked mole rats, like their social structure, their physiology and behavior, it's like, OK, so here's another really wacky thing," says Park. "But it's really, really cool."

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