The naked mole rat may not be the most attractive rodent on the block, but it’s still a social butterfly. These hairless, mostly blind and deaf animals live in colonies of up to 300 individuals, which communicate with high-pitched squeaks. Now, researchers have discovered that, like humans and many birds, mole rat communities have their own dialect, which is kept alive by their queen.
“The study is exciting because it provides the first evidence for vocal learning in a rodent,” says evolutionary biologist Tecumseh Fitch at the University of Vienna, who was not part of the work. More research, he says, may help scientists better understand how complex vocalizations evolved in social animals, including humans.
Naked mole rats (Heterocephalus glaber) are renowned for a vast list of weird features: They rarely get cancer, for instance, they live longer than any other rodent, and they have a high pain tolerance. Researchers became interested in them in the 1970s because they are also a rare example of mammals living—like bees and ants—in colonies of workers ruled by a single breeding matriarch or “queen.” Scientists knew naked mole rats used chirps to communicate, but until now, they had no idea how complex their vocalization was.
The new study started by recording the greeting sound naked mole rats emit when they meet each other: a soft chirp. Over 2 years, researchers logged more than 36,000 of these chirps from 166 animals living in seven colonies in German and South African labs.
To make sense of the sounds, the team developed a software that automatically classified the sounds by their acoustic features. The program could identify the voice of specific mole rats, revealing that each colony had its own distinct chirp, characterized by differences in their sound wave pattern and pitch. When the scientists played the sounds back, the rodents were more likely to respond with chirps when the vocalizations came from their own colony, the team reports today in Science.
To be sure the animals were reacting to their colony’s dialect rather than a familiar voice, the researchers created an artificial sound that had features of a particular colony’s dialect. Mole rats were more likely to respond to the artificial sound from their own colony than to one sporting a foreign colony’s signature, the team found.
“They can recognize their own dialect,” says study co-author Alison Barker, a neurobiologist at the Max Delbrück Center for Molecular Medicine. She says she spent so many months listening to the rodents, she can now identify each colony’s dialect by ear.
The researchers think the mole rats developed the dialects to spot interlopers. Naked mole rats are incredibly violent toward foreigners, usually killing intruders. Because they live in darkness and are nearly blind, using sounds is their best way to suss out an invader, the researchers say.
“They’re very xenophobic, so they want to make sure that they stay within their own tribe,” says co-author Gary Lewin, a neurobiologist at Max Delbrück. “Having a dialect is a way to keep the social bond alive.”
The team further showed that the naked mole rats learn their colony’s dialect when they are young. When the researchers placed newborn pups in foreign colonies, the orphans adopted the new colony’s dialect within 6 months.
However, as with human language, the naked mole rat dialects can also disappear as society changes. By chance, during the experiments, two queens were overthrown and killed. The dialects of their colonies faded until a new queen was selected and a new dialect was established. “Without a queen, a few members of the colony become kind of free” and started to abandon the dialect and speak in their own way, says Barker, who doesn’t know yet how the sovereign exerts control over the way her subjects speak.
“It is an elegant and technically superb study,” says Thomas Park, a biologist at the University of Illinois, Chicago, who has been working with naked mole rats for more than 20 years. He would like to see more research with the pups “to tease out what parts of their vocalizations are genetically determined versus learned.”
Both Park and the study authors think mole rats can help scientists better understand how learned vocal communication evolved in different animals. Barker’s and Lewin’s team has already started to investigateg traces of language evolution in the rodent’s genome. “If we find what makes a social brain in a mole rat,” Lewin says, “this will give us deep insight about what makes humans vocal and social.”