Naked Mole Rats Have Their Own Tower of Babel, Science Surprised to Learn

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Naked mole rats are eusocial animals. Within their colonies, there is a strict hierarchy that affects how the rodents overtake each other in their tunnels. They also chirp constantly – for example, to greet each other.
Naked mole rats are eusocial animals. Within their colonies, there is a strict hierarchy that affects how the rodents overtake each other in their tunnels. They also chirp constantly.Credit: Colin Lewin
Ruth Schuster
Ruth Schuster

The wonder that is the naked mole rat just delivered yet another zinger. The bizarre, eternally youthful, xenophobic little animals live in colonies – and it turns out each colony has its own language, a team led by molecular biologist Gary Lewin at Berlin’s Max Delbrück Center For Molecular Medicine reported in Science on Thursday.

Moreover, it seems that among her other duties, each colony’s queen is responsible for preserving the exclusive dialect. When she dies, anarchy ensues, including in their vocalizations. Dialect integrity is only restored with the advent of a new monarch.

Yes, the naked mole rat (Heterocephalus glaber) is a communicative little beastie, emitting a wide range of sounds. You can hear them vocalizing – chirping, squeaking, twittering or even grunting – if you can bear to observe them closely near their subterranean nest.

“Their vocal repertoire is comprised of at least 20 sounds, which is on the order of vocal repertoires observed in nonhuman primates,” says lead author Alison Barker.

The discovery of colony-specific naked mole rat tongues was serendipitous. Given the subterranean rodents’ rigid division of labor and behavioral patterns, Prof. Lewin wondered, as molecular biologists do, whether the mole rat’s vocalizations fulfilled a social function. It was while trying to analyze mole rat greetings that Lewin and the team realized that each colony has its own dialect, Barker explains.

A naked mole rat speaks

Before we get to how the researchers deduced and proved the thesis of the Tower of Naked Mole Rat Babel: why would naked mole rats develop a colony-specific form of communication?

Naked mole rats are a xenophobic bunch who react negatively to “foreign” naked mole rats (i.e., from other colonies). The team suggests that the development of colony-specific dialect strengthens cohesion and the sense of belonging among the naked mole rats of the specific colony. These may number up to a few hundred individuals, consisting of the one queen – the only one to procreate – and male and female subjects.

It bears adding that the queen may mate not only with specific consorts in the colony but with a roaming foreign male, which prevents inbreeding but adds to the weirdness. Perhaps pillow talk isn’t part of the naked mole rat vocal repertoire.

Naked mole rat eating a food pelletCredit: Felix Petermann, MDC

Within the underground colony the naked mole rats are amiable to one another, regimented and manage their affairs harmoniously, the team says. They eat primarily tubers and sometimes their own feces, which may be part of their eusocial adaptations.

Lewin postulates that their inter-colony antagonism arose as an adaption to the perennial shortage of food in their natural habitats.

Asked if the phenomenon is unique to the naked mole rat among the greater group of mole rats, Barker tells Haaretz that many mole rat species use vocalizations, but not to the extent seen in the naked types with their repertoire of at least 20 vocalizations. “Naked mole rats show a remarkable flexibility in dialect acquisition at young ages. Pups that were moved from their birth colony to a foreign colony were able to learn features of the adoptive dialect,” she says.

Vocal learning of the type has been well established in humans, birds, cetaceans – whales and dolphins – and now rodents, Barker adds.

Naked mole rats are very communicative creatures. They quietly chirp, squeak, twitter or even grunt to one another. Credit: Felix Petermann, MDC

We note that among the differences between the naked mole rat and other mole rats is the fact that the naked mole rat is mostly bald, it has hairs sticking out here and there, mainly from its face and rump, while the others are furry.

AI and the naked mole rat

How was naked mole rat dialect discovered? The scientists recorded 36,190 chirps made by 166 individuals from seven naked mole rat colonies maintained in labs in Berlin and Pretoria. (We note that they exist in Israel too.)

The mathematician Grigorii Veviurko, who is now at Delft University of Technology, then applied an algorithm to the sounds, analyzing the acoustic properties of the individual vocalizations based on specific factors.

Veviurko also trained artificial intelligence to reliably detect which chirps came from which individual naked mole rat and to identify the characteristics of each colony’s sounds. The AI could even tell which colony a given naked mole rat came from – and that was exactly the point at which the scientists realized that, apparently, different colonies had different dialects.

Lewin’s team recorded a total of 36,190 chirps made by 166 individuals from seven naked mole rat colonies, and used an algorithm to analyze the acoustic properties of the individual vocalizations.Credit: Felix Petermann, MDC

But could the little animals tell that, and distinguish friend (colony mate) from foe (anybody else)? To test that, the researchers had the software create sounds that featured characteristics of the colony’s dialect, but did not resemble the voice of a specific naked mole rat.

Naked mole rats reacted to chirps from friends and ignored chirps from foes – and also responded to the computer’s chirps. They even only responded to community-type chirps when the researchers wafted the scent of a foreign colony into the test chamber.

And that, the researchers concluded, meant the mole rats were responding to the dialect, not to an individual they knew and could tolerate.

A small side experiment with three orphaned naked mole rat pups placed into colonies where the queen had recently littered (to assure the dear animals wouldn’t slaughter the alien babies) found that they learned the adopting colony’s language.

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.Credit: Felix Petermann, MDC

As for the monarchal control of tongue: “During the course of the study, one of our colonies lost two queens within relatively quick succession,” Lewin says. “In the anarchy that ensued, we observed that the vocalizations of the other naked mole rats in the colony began to vary much more widely than usual. Dialect cohesiveness was thus greatly reduced and didn’t return until a few months later, with the ascendance of another high-ranking female as the new queen.”

It takes a colony of fruit bats

Fruit bats are also quite the linguists. In 2017, a report in Nature revealed language acquisition by baby Egyptian fruit bats – another animal that lives in colonies with social structuring.

“It takes a village to teach a bat how to communicate,” author Rachael Lallensack wrote. The baby fruit bats learn calls from their mothers, but she found they can pick up new dialects, or the pitch of their vocalizations, from colony members around them.

“Vocal learning” by repeating the sounds other make had been thought to be the fief of humans and cetaceans, and song birds, but we shall put aside the avians, whose brains work differently. Now we know bats and naked mole rats have the knack too, which is a convenience for research. Lallensack noted that it’s a lot easier to study bats in the lab than whales; the same goes for naked mole rats, with the caveat that they live in pitch-dark tunnels and are bitey. At least they can’t escape by flying away.

Bats live in colonies that may number in the thousands. Highly organized societies rely on elaborate mechanisms for communication, Barker explains.

Over millions of years, naked mole rats have cast away everything underground that uses their energy and isn’t necessary to survive. This includes their fur – but also results in surprising abilities.Credit: Felix Petermann, MDC

“In this sense, it is perhaps not so surprising that naked mole rats – which are one of only two eusocial mammals living in highly cooperative social groups characterized by a single breeding female (queen), and most commonly found in ants, bees and wasps – are highly vocal,” Barker says. “What is perhaps surprising is how important the queen is for maintaining dialect integrity. When we tested if naked mole rats could distinguish their own colony dialect from other colonies, we found they were very good at it. Yet we demonstrated that when the queen is lost, the cohesiveness of the dialect disintegrates. This suggests that social order may be actively maintained through dialect usage, in part by one very dominant ruler.”

Dialect is just the latest wonder ascribed to the naked mole rat. Their longevity is astonishing, which one study ascribed to perennial hypoxia: their existence in tunnels with low oxygen and high carbon dioxide. The naked mole rat lives about eight times longer than other rodents its size. Procreation actually extends its life span even more, in contrast to every other animal – which is physiologically illogical. It barely gets cancer, and famously doesn’t evince signs of aging: no evidence of neurodegeneration has been detected even as the rodent enters its third decade. One day they suddenly flop over and die.

Naked mole rats in Israel have been ascribed archaeological prowess. Their colonies can be vast, a few hundred meters in length, and as the diggers throw out dirt, they have been known to throw out artifacts. Small ones at least. And it was the naked mole rat who led to the 2018 discovery of a Davidic-period palace in a Canaanite town that apparently had allied with a powerful Judahite kingdom, lending support to the theory of the United Monarchy. Respect.

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