Naked mole rats have accents

Naked mole rates are bizarre creatures that can live for up to 32 years and are totally insensitive to pain caused by acid or the spicy ingredient in chilli peppers! They’re also highly cancer-resistant, and can survive for hours in extremely low oxygen air. They are unfortunately also extremely ugly. But now, pulbished in the journal Science, scientists can add a new item to the naked mole rat CV; it turns out that they speak to each other, and they do it in different dialects. Eva Higginbotham heard how from Gary Lewin, from the Max Delbrück Center for Molecular Medicine in Berlin...

Gary - Naked mole rats are moles that live underground and they come from East Africa, and they live in desert regions where there's not a lot of vegetation. They are very unusual because they live underground in very large colonies and the colony can be up to 300 animals, but on average, it's about 40 animals. These animals are really strange because they also have a queen just like ants and bees. And when you keep mole rats, you realise that they're always, constantly, seem to be talking to each other in the colony. And so we were interested to see what these sounds are for, and that's when we started to look. The most common vocalisation really sounds like a bird - it's called a soft chirp. We decided to analyse these soft chirps, and so we looked at thousands of these soft chirps, and we figured out with a very special mathematical program that actually every single animal has its individual soft chirp. So each animal had its own voice.

Eva - How did you actually make these recordings of the mole rats? Were you sort of taking a mole rat and holding it up to a microphone and hoping it would make some noise?

Gary - More or less yeah, so we take each individual animal out and put it in front of a microphone and push it gently and then they will start to vocalise. And we did this hundreds and hundreds of times to get thousands and thousands of vocalisations. Now the soft chirp is only one of 24 vocalisations that the mole rat makes, but it makes up over 90% of all of their vocalisations. We don't know what it means, but we kind of guess that it's like a greeting call. So it's like a hello, hello, kind of call.

Eva - I see, so mostly they're just going around saying hi! Hi Hi! Hi! Hi - all the time!

Gary - Exactly. Yeah. We then also went on to use the same algorithm to ask whether different colonies have different voices. And it turns out that each colony seems to have its own distinctive dialect that was figured out by the machine learning algorithm. But we wanted to see if that's really used by the animals, so we did an experiment actually, where we played back soft chirps to an animal and asked whether the animal would answer the chirp if it was from its own colony or if it was from a foreign colony. And it turns out that the mole rats would chirp back to a loudspeaker if the chirp was from its own colony, but not from a foreign colony. And you have to be aware that these naked mole rats are rather like humans in the sense that they're very xenophobic - so if a member of another colony comes into their colony, they will actually almost immediately recognise this animal as a foreigner and kill the animal. And so we figured out that maybe the dialect of the animals is actually a way that the animals can use to identify foreigners that might come into their colony.

Eva - Where do you think the animal acquires its accent or its dialect from, do you think it's somehow genetic?

Gary - We don't think it's genetic because we specifically asked whether dialects can be learned by young animals. So we were able to foster baby mole rats from one colony into another colony. And indeed what they do is they really adopt the new dialect. So as they're growing up in the first six months of their life, as long as they're exposed to the dialect, they will learn that dialect. So it seems to be very important that the animal adopts the dialect so that he's at home and recognised as a member of that colony.

Eva - What do you think we can learn about how other animals communicate by understanding how mole rats communicate?

Gary - I think one thing that is very important here is that the mole rat has been around a lot longer than we have. We know that the mole rat has been around for at least 20 million years. And so they already display features of a vocal culture, that means a culture that is learned from their peers, and we often think that's something that is unique to humans. But what's interesting about the mole rat is that we can actually study in the laboratory what is the difference between a mole rat brain and let's say the brain of a mouse, which is not at all social, to see how evolution came up with this sociality, this ability to live in a society together. So we think we can learn a lot about being social by studying the biology of the naked mole rat.