Humans aren't the only creatures with dialects that are specific to certain regions. It seems that colonies of naked mole-rats have their own dialects too, which strengthens the social connections of these very communicative creatures that can chirp, grunt, and squeak. The findings have been reported in Science.
"We wanted to find out whether these vocalizations have a social function for the animals, who live together in an ordered colony with a strict division of labor," said the study leader Professor Gary Lewin, head of the Molecular Physiology of Somatic Sensation Lab at the Max Delbrueck Center for Molecular Medicine in the Helmholtz Association (MDC).
An international team of researchers analyzed the noises that naked mole rats made when greeting one another. Over two years, Lewin's team recorded 36,190 chirps vocalized by 166 individuals that were part of seven colonies in labs in Berlin and Pretoria.
"In so doing, we established that each colony has its own dialect," noted the lead study author, Dr. Alison Barker of MDC. "The development of a shared dialect strengthens cohesion and a sense of belonging among the naked mole-rats of a specific colony."
These creatures usually work in harmony when they're part of the same colony, and they each have their own roles that they carry out. But the research showed that naked mole-rats can tell when one isn't a member of their established colony, and it seems they don't care for outsiders.
"You might even say that these animals are extreme xenophobes," said Lewin, who suggested they may act that way because food is scarce in their habitat: the dry plains of East Africa.
An algorithm was developed by mathematician Grigorii Veviurko to assess the acoustic characteristics of the individual vocalizations, and a computational tool was trained to determine which naked mole-rats made which noises. This work showed that each animal had its own voice. Next, the researchers set out to determine whether the animals could recognize one another's voices and if they could distinguish dialects.
The researchers developed a behavioral test in which the naked mole-rats had the option of moving through a tube towards the sound of another naked mole-rat, or towards silence.
"We observed that the animals always immediately headed for the chamber where the chirps could be heard," said Barker. When the chirps came from another member of the animal's colony, it would immediately respond vocally; when the sounds came from a member of a different colony, the animal would then stay silent. "That enabled us to infer that naked mole-rats can recognize their own dialect and will selectively respond to that."
Further research showed that the naked mole rats would respond to computer-generated chirps that were made to sound like another colony member, even if it was accompanied by the scent of another colony.
"That demonstrated that the naked mole-rats were responding specifically to dialect rather than scent, and that they have a positive reaction to hearing their own dialect," said Lewin. "Naked mole-rats have a linguistic culture that developed long before human beings even existed. The next step is to find out what mechanisms in the animals' brains support this culture because that could give us important insight into how human culture evolved."