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Twittering, squeaking, chattering: the naked mole rat communicate in different sounds, some of which are reminiscent of birds chirping
Photo: Felix Petermann / MDC / dpa
Evolution, that much is certain, has not exactly endowed the naked mole rat with beauty.
The rodents that are native to Africa have so little hair that you can see every wrinkled fold of skin.
But where the naked mole rat (Heterocephalus glaber) lives, it is fortunate that it does not depend on the appearance.
In the underground colonies where the animals live, darkness envelops the animals' appearance.
In addition, naked mole rats have developed so many wonderful properties that their appearance is of secondary importance: the animals do not develop cancer, have hardly any pain sensation, become very old for rodents and can get along for an exceptionally long time without oxygen.
Like insects with a queen, they live organized in states - a very rare behavior in mammals.
And in addition, the animals speak dialects with which they communicate, researchers from the Max Delbrück Center for Molecular Medicine (MDC) in Berlin and the University of Pretoria (South Africa) now write in the journal “Science”.
The journal even dedicated its cover to the animals.
Naked mole rats chirp, squeak, chatter or grunt and are extremely communicative beings.
Each colony has its own dialect, which distinguishes it from other colonies and strengthens the cohesion of its own group.
The team led by MDC researcher Alison Barker concentrated on a sound that the animals uttered in greeting, a faint chirping.
Altogether at least 17 different sounds of naked mole rats are known.
In two years, the scientists recorded more than 36,000 of the soft chirping sounds of 166 animals.
The naked mole rat came from colonies that were kept in laboratories in Berlin and Pretoria.
The researchers used an algorithm to analyze the acoustic characteristics of each sound.
"This enabled us to record and compare eight different factors, such as the height or the asymmetry of the curve obtained in this way," explains Gary Lewin, who also works at the MDC, in a press release.
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In the wild, naked mole rats live in the semi-deserts of East Africa
Photo: Felix Petermann / MDC / dpa
The researchers finally developed a computer program that, after a certain training phase, was able to assign the sounds to individual animals.
"We now knew that every naked mole rat has its own voice," says Barker.
The computer program also recognized differences between the chirping of different colonies, so it was able to assign individual animals based on their sounds.
It was unclear whether the animals recognized their dialect and could distinguish it from others.
To find out, the scientists placed a naked mole rat in a test field, consisting of two chambers that were connected to one another by a tube.
In one room chirping sounds were played, in the other it was quiet.
"We observed that the animals always immediately went to the chamber with the played sounds," said Barker.
When they heard the sounds of their own colony, they answered too.
Otherwise they mostly remained silent.
The queen says where to go
To find out whether the rodents reacted to their dialect or were chattering because they simply heard a conspecific they knew, the scientists carried out a second experiment: They played the animals artificially made sounds that had characteristics of the dialect in question, but not resembled the sound of a single animal.
The naked mole rats reacted to the artificial sounds as to the natural ones - so they recognized their dialect.
This even worked when the scientists combined the sound of one colony with the scent of another.
Young animals that are moved to another colony shortly after birth learn the sounds of their new community, the scientists report.
Finally, the researchers discovered that the queen of a colony - the only female to have offspring - is responsible for the linguistic cohesion of her group.
If a queen died, the sounds of the colony developed wildly in the following years, they varied much more.
Only a new queen brought acoustic order back into the group.
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Naked mole rat recording sound in the laboratory
Photo: Felix Petermann / MDC / dpa
Rochelle Buffenstein writes in a commentary on the study that the mole-nosed mole rat learns the language of humans or the songs of whales.
This requires the ability to save the perceived sounds, remember them and then reproduce them.
"This is an astonishing achievement for a rodent and is in marked contrast to the vocalizations of the majority of mammals, which are innate, invariable and genetically inherited."
MDC researcher Lewin also says that humans and naked mole rats have more in common than one would assume.
"Naked mole rats have a language culture that developed long before humans even existed." The task now is to find out which brain mechanisms would produce this service.
This allows conclusions to be drawn about the development of human culture.
The natural habitat of the naked mole rat are the semi-deserts of East Africa.
There the animals live in colonies of 20 to 300 animals.
There is only one queen in each colony.
The other animals take on different tasks depending on their age, such as digging new passages or guarding the entrances.
Members of other colonies are aggressively attacked and some are killed.
In 2017, a team led by Lewin reported that naked mole rats can survive for a full 18 minutes without oxygen.
If the air becomes scarce, they change their metabolism so that vital organs such as the heart and brain can continue to be supplied.
The rodents are also quite insensitive to pain, acid or heat stimuli trigger no or significantly weaker pain sensations in them.
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joe / dpa
