Ground-breaking study reveals colonies of mole-rats communicate with each other in their own dialect

A study by a team of scientists at the Max Delbrück Center for Molecular Medicine (MDC) in Berlin, Germany and the University of Pretoria (UP) has found that naked mole-rats can communicate with one another within their own colony. They do this with a unique dialect that is specific to that individual colony.

Naked mole-rats – rodents with a wrinkled, pink skin and large protruding teeth – live in large, underground families. Most studies to date have been focused on their unique physiological qualities, namely that they rarely get cancer, are resistant to some types of pain, can survive up to 18 minutes without oxygen, and live into their mid-30s, a remarkable feat for a small rodent. 

“Naked mole-rats, one of only two eusocial (an extreme version of social group living) species of mammals, use shared dialects to strengthen unity of their large colonies,” reports the team, whose research article is featured on the cover of the prestigious journal Science. “The social and communication skills of human beings and naked mole-rats appear to have much more in common than anyone might have previously thought. Naked mole-rats have a linguistic culture that developed long before human beings even existed.”

“Naked mole-rats are very communicative creatures,” said Professor Gary Lewin, Head of the MDC’s Lewin Lab focused on the molecular physiology of somatic sensation. “If you stand outside their home and listen, you can hear the little rodents quietly chirping, squeaking, twittering, or even grunting to one another. We wanted to find out whether these vocalisations have a social function for the animals, who live underground together in an ordered colony with a strict division of labour.”

According to Professor Nigel Bennett, holder of the South African Research Chairs Initiative (SARChI) chair in Mammalian Behavioural Ecology and Physiology at UP’s Department of Zoology and Entomology in the Faculty of Natural and Agricultural Sciences, “Like other eusocial organisms such as termites, ants and bees, naked mole-rats live in large groups of around 40 to 50 animals which, in exceptional cases, can reach up to 300 with only one reproductive female, the queen, and one to three of the larger males responsible for reproduction. The remaining colony members are reproductively suppressed. Many species of mole-rat, naked mole-rats in particular, are extremely vocal, and it is of no surprise that they can identify one another by their vocalisations.”

The MDC and UP team, which includes Professor Gary Lewin, Dr Alison Barker, Lina Mograby, mathematician Grigorii Veviurko (who is now at the Delft University of Technology in the Netherlands), Professor Bennett and Dr Daniel Hart, set out to closely analyse the chirps that the naked mole-rats use to greet one another. “In so doing, we established that each colony has its own distinct dialect,” reports Dr Barker, lead author of the study. “The development of a shared dialect strengthens cohesion and a sense of belonging among the naked mole-rats of a specific colony.”

In order to analyse the naked mole-rats’ language, over a period of two years the research team recorded a total of 36 190 chirps made by 166 individuals from seven naked mole-rat colonies held in laboratories at Berlin and at UP. Prof Lewin’s team used an algorithm to analyse the acoustic properties of the individual vocalisations. “That enabled us to collect and compare eight different factors, such as the height or level of asymmetry in the sound spectrogram,” explained Prof Lewin.

Veviurko also developed a computer programme that, after an initial training period, was able to reliably detect which chirps came from which individual naked mole-rat. “We knew that each naked mole-rat has its own voice. What we did not know, however, was whether the animals could recognise one another from their voices,” Dr Barker said.

The computer programme, which uses artificial intelligence, did not only identify the animals on the basis of their individual voices, but also detected similarities in the types of sounds made within a single colony. The programme was able to identify which colony a specific individual came from. “Surprisingly, that meant that each colony probably had its own distinct dialect,” Dr Barker said. At that point, the research team did not yet know whether the animals were aware of that, and whether they could recognise their own dialect and distinguish it from others.

After a series of playback experiments it was observed that if the sounds were made by an individual from the test subject’s own colony, it would give an immediate vocal response, but if they were made by an individual from a foreign colony, the mole-rat would remain silent. “That enabled us to infer that naked mole-rats can recognise their own dialect and will selectively respond to that,” Dr Barker said. In further experiments the researchers placed three orphaned naked mole-rat pups in foreign colonies where the queen had also recently had a litter. Six months later, the computer programme showed that the foster pups had acquired the dialect of their new home.

The team said the next step is to find out what mechanisms in the animals’ brains support this culture of communication, as this could provide important insights into how human culture evolved. With access to many other species of African mole-rats and with hundreds of hours of observation on the only other eusocial mammal species (the Damaraland mole-rat) under his belt, Prof Bennett believes that this is only the tip of the iceberg, and that with further analysis and continued collaboration with the world’s best at the MDC, the evolution of vocal communication lies at the tips of our fingers.

Click on the gallery in the sidebar to view a selection of images showing how mole rats live and communicate.

Researchers

• 

  Professor Nigel Bennett

  Professor Nigel Bennett has been at the University of Pretoria (UP) for 26 years. He holds a BSc (Hons) in Zoology, which he obtained at Bristol University in the UK, and undertook his PhD studies at the University of Cape Town.
  
  His research focus is animal physiology and behaviour using the African mole rat as his model animal. His work is directed primarily at studying the social regulation of reproduction in mole rats.
  
  Prof Bennett’s research record ranks him among the best researchers studying social regulation of reproduction in any group of mammals in the world. He has investigated cooperative breeding in mammals from a variety of perspectives. This multi-faceted approach has led to an integrated understanding of reproductive suppression in mole rats of a type that has not been achieved for any other taxa. His research has set the benchmark for our understanding of phylogenetic and ecological constraints that regulate reproductive success and social evolution in mammalian species.
  Prof Bennett has always been interested in why some organisms adopt a social lifestyle and others do not. As a young boy, he was fascinated by how wood ants worked for the common good of a queen. His interest in mole rats came about while he was an undergraduate at Bristol University, after he had read a seminal paper by scientist Jennifer Jarvis on cooperative breeding in the naked mole rat. Upon obtaining a position as a doctoral candidate, Prof Bennett wanted to see if this was a feature common to other African mole rats. He went on to study the Damaraland mole rat, and found it to have incredible social organisation similar to that of social insects and termites.
  
  Prof Bennett is now the world leader in African mole rat biology, particularly in reproductive physiology. A research milestone for him was discovering that breeding female naked mole rats orchestrate non-breeding males and females in the colony to exhibit high prolactin levels. This inhibits the release of hormones that stimulate the development of reproductive activities in the gonads, as evidenced by a lack of follicular development in ovaries and a reduction in numbers and motile sperm in testes. Prolactin also results in individuals exhibiting helping behaviour and cooperative care of the young.
  
  After nearly three decades of research on the reproduction of social African mole rats, Prof Bennett has not been able to determine how the breeding female actually inhibits reproduction in physiologically suppressed animals. This would be the magic bullet for potential contraception in humans.
  He leads a research group that strives to unravel how social evolution arose in African mole rats – solving this puzzle has important implications as to how social evolution arose among hominids. Essentially, it comes down to food acquisition and protection from predators, which is a central theme in social evolution in most mammalian groups.
  
  Two people influenced his career: Prof Brian Follett – who supervised Prof Bennett’s honours project and whose infectious enthusiasm for science and incredible lectures fired up Prof Bennett’s imagination – and Prof Jennifer Jarvis, who drove his passion to work on mole rats.
  
  In 2021, Prof Bennett was made an honorary member of the American Society of Mammalogists, a title bestowed on fewer than 100 luminaries in a century. He has been a visiting professor at the School of Chemical and Biological Sciences at the University of London’s Queen Mary College since 2005. More recently, he was a visiting professor at the Department of Zoology at King Saud University in Saudi Arabia.
  
  He is a member of the Academy of Science of South Africa, and a fellow of the Zoological Society of London, the Royal Society of South Africa and the African Academy of Sciences.
  
  Prof Bennett was awarded the UP Chancellor’s Medal for his research on three occasions and has received the Exceptional Academic Achiever Award for the past 14 years. He was also the recipient of the Zoological Society of Southern Africa’s gold medal and received the Havenga Prize for outstanding contributions to Life Sciences, awarded by the Academy of Science and Arts of South Africa. UP awarded him the University of Pretoria Commemorative Research Medal for being one of the top 100 scientists in 100 years of its existence.
  
  Prof Bennett has served as president of the Zoological Community of Southern Africa for two years. He is also editor-in-chief of the Journal of Zoology and a past editor of Proceedings of the Royal Society B: Biological Sciences. In 2013, he was the handling editor of Biology Letters, another Royal Society of London journal. He has published 433 papers in international peer-reviewed scientific journals, co-authored a specialist book published by Cambridge University Press and has penned 15 chapters in books.
  
  In his spare time, Prof Bennett travels to different countries in Africa to explore the wildlife. He particularly enjoys visiting the mountain gorillas in Rwanda and Uganda, and the eastern lowland gorillas of the Democratic Republic of the Congo. He is also an avid collector of African art and frequently visits markets to add to his collection.
  
  If he were not a researcher, Prof Bennett would have liked to have been a game warden in one of East Africa’s national parks to contribute to the protection of the incredible African fauna from poaching.
  
  ORCID ID: 0000-0001-9748-2947
  

  More from this Researcher
• 

  Dr Daniel Hart

  Dr Daniel Hart is a postdoctoral fellow at the University of Pretoria. His research focuses on the evolutionary physiological and biomedical studies of African vertebrates.
  
  Dr Daniel Hart was part of an international team with Prof Nigel Bennett whose research into African mole-rats was not only published in the distinguished journal Science but made the cover.
  
  Prof Nigel Bennett, a professor in UP’s Department of Zoology and Entomology, and post-doctoral fellow Dr Daniel Hart worked closely with the Max Delbrück Center for Molecular Medicine in Berlin, Germany on their recent research, the findings of which show that mole-rats communicate in their own dialect.
  
  He tells us more about their groundbreaking research.
  
  What makes African mole-rats so interesting?
  DH: They are great models to show how animals adapt to their environment. For example, their broad spectrum of sociality has been brought about by the different species inhabiting different climatic regions. Simultaneously, their incredible ability to withstand hypoxic (low oxygen) conditions has come about because of their exclusive subterranean lifestyle.
  
  What made you focus your research on them?
  DH: When I began my research career, a wise mentor gave me a piece of advice: study animals that you can ask interesting questions about. So far, I have not found an animal that you can ask more interesting questions about than African mole-rats ­­– the number of exciting questions and answers that mole-rats have to offer drew me to studying them.
  
  How does their social and communication habits have an impact on how we understand them?
  
  DH: Naked mole-rats live in large families (50 to 60 individuals), with some colonies reaching 300, controlled by one female, the queen. Each colony member has its own “job”, and everyone recognises their own colony and family members, even in the dark. Even after the vast number of studies on these amazing animals, how the colony structure is maintained has somewhat eluded us. But, like humans, it may come down to dialects to some extent. From this study, we have learnt that each mole-rat colony has its own dialect, dictated by the queen, allowing colony cohesion and detection of intruders. Interestingly, this dialect can be learnt, which is an uncommon ability in most animals. This new understanding brings us closer to figuring out how these large families work together and stay together. This understanding can possibly help us in furthering our knowledge about human dialects.
  
  Are there any other animals that provide as interesting an array of applications as the mole-rat?
  
  DH: We are fortunate, as Africa has a treasure trove of unique animals with remarkable features and abilities. One such animal we are working on is the tenrec, which is a fantastic model of a prehistoric mammal. With these animals, we hope to peer back in time to unravel essential questions about evolution. Like the mole-rats, they also possess remarkable physiological and molecular traits, which could be vital to biomedical studies.
  
  What do you do in your spare time?
  DH: I have quite a big interest in other scientific subjects, namely astrophysics, astronomy and cosmology. I also enjoy listening to books or podcasts on these subjects and reading articles when I get a chance. Also, I am passionate about sport, so I enjoy catching up on the world’s sporting events when I can.

  More from this Researcher

Related Gallery

• 

  Ground-breaking study reveals colonies of mole-rats communicate with each other in their own dialect