Friend Or Foe? Naked Mole Rats Can Tell By A Unique Squeak

Jan 28, 2021
Originally published on February 1, 2021 1:04 am

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.

The algorithm was able to very reliably detect which chirps came from which individual naked mole-rat. So each naked mole-rat has its own distinctive voice.
Felix Petermann, MDC

"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, says 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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ARI SHAPIRO, HOST:

Naked mole rats are, as the name suggests, almost hairless creatures. They are mostly blind and live underground in arid parts of Africa. Now, scientists have learned something surprising about how these creatures talk to each other. NPR's Nell Greenfieldboyce reports.

NELL GREENFIELDBOYCE, BYLINE: Alison Barker thinks naked mole rats are sweet and cute. Others see them differently.

ALISON BARKER: Often people think, oh, it's that really weird, ugly animal with the big teeth and the wrinkly skin.

GREENFIELDBOYCE: Barker studies naked mole rats at the Max Delbruck Center for Molecular Medicine in Berlin, Germany. And she says they are really unusual rodents. They can live more than 30 years. They're resistant to cancer and certain kinds of pain. Plus, they're cold-blooded. What intrigued Barker was their constant bird-like chirping.

(SOUNDBITE OF NAKED MOLE RAT CHIRPING)

GREENFIELDBOYCE: She wondered if these calls were involved in maintaining this species' complex social structure. Each naked mole rat colony is ruled by a queen, who mates with just a few males and gets to have all the babies. Everyone else works for the common good. Barker and her colleagues spent a lot of time recording and cataloging naked mole rat calls.

BARKER: We can say now that there's about 25 different sounds that they make.

GREENFIELDBOYCE: One of the most common is a greeting, the soft chirp.

(SOUNDBITE OF NAKED MOLE RAT CHIRPING)

BARKER: And so if you're a naked mole rat and you were walking in the tunnel and you bump into another naked mole rat, which happens quite frequently, actually, you would both emit your own soft chirp.

GREENFIELDBOYCE: The research team focused in on this chirp, recording more than 36,000 examples from 166 naked mole rats living in seven colonies. In the journal Science, they report a surprising finding. Each colony has its own dialect. Its soft chirp is acoustically distinct. When the researchers played soft chirps to naked mole rats in the lab...

BARKER: Almost all of the time, they only responded when they were presented with a dialect that matched that of their home colony.

GREENFIELDBOYCE: To hear the difference in soft chirps, here's some from their lab colonies, which are named after the groups in "Game Of Thrones," like the Martell Colony...

(SOUNDBITE OF NAKED MOLE RAT CHIRPING)

GREENFIELDBOYCE: ...The Arryn Colony...

(SOUNDBITE OF NAKED MOLE RAT CHIRPING)

GREENFIELDBOYCE: ...And the Dothraki Colony.

(SOUNDBITE OF NAKED MOLE RAT CHIRPING)

GREENFIELDBOYCE: To human ears, these differences might seem small, but in naked mole rats, they could lead to some "Game Of Thrones"-style clashes because naked mole rats will attack foreign strangers. Very young pups, however, can be moved from one colony to another. And Barker found that pups will learn to speak the dialect of their adoptive home. A colony's dialect seems to be controlled by the queen. When she dies, there's chaos and infighting and soft chirps sound more variable until a new queen establishes herself.

BARKER: And so we actually think that one of the ways in which the queen maintains her control is to make sure that everyone is, like, rigidly adhering to a certain dialect. And so that becomes, perhaps, a readout for conformity within the colony.

GREENFIELDBOYCE: These findings fascinated Rochelle Buffenstein, a researcher who studies aging in thousands of naked mole rats at Calico Life Sciences.

ROCHELLE BUFFENSTEIN: To me, it appears that naked mole rats are clearly able to learn vocalizations in much the same way that humans and songbirds do and create this language through vocal mimicry, which is unheard of in other rodents.

GREENFIELDBOYCE: And this could give scientists a new way to study the biology of language learning in the lab.

Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.