“Chatty Turtles” reverses the script about the evolutionary origins of vocalization in animals

Pakinam Amer: This is Scientific American’s 60 Second Science. I am Pakinam Amer.

Clicks, cackles, grunts and snorts – these are not sounds we normally associate with turtles.

[CLIP: Audio of South American juvenile turtles]

Amer: They are actually considered to be very quiet or even silent. But it looks like we grossly underestimated how much sound they can make. Now a new study in Nature Communications has collected voice recordings of 53 species of turtles and other animals otherwise thought to be mute.

[CLIP: Audio of South American juvenile turtles]

Amer: Those clicks you just heard were calls from baby giant tortoises in the Amazon swimming together. A group of evolutionary biologists and other scientists in five different countries pored over these recordings and combined them with vocal repertoires of about 1,800 animal species from other studies.

Amer: They were able to piece together evidence that the last common ancestor of all lungfish and tetrapods began speaking more than 400 million years ago. (And just in case you’re not familiar, tetrapods are four-limbed vertebrates that include amphibians, mammals, birds, and reptiles.) That’s at least 100 million years earlier than previous studies suggested.

Amer: The new revelations amount to a rewriting of the sonic history of animals with backbones.

Gabriel Jorgewich-Cohen: I was doing fieldwork in the Brazilian Amazon with a researcher who published one of those first papers showing that turtles could communicate acoustically, and that inspired me. So I went back home, got a device and started adopting my own pets. And I discovered that they also made noise, and the species that I had weren’t known to make noise. So I started thinking maybe they all do, and I went out and recorded as many as I could [laughs].

Amer: That was Gabriel Jorgewich-Cohen, a researcher at the University of Zurich and co-author of the study. By the way, the pets he’s talking about are Amazon giant tortoises, better known in the US as red-eared sliders.

Jorgewich-Cohen: This is the only species known to have post-hatch parental care among all tortoises, which is quite amazing. And they discovered this by recording the sounds of the animal – not just this species, but also sea turtles,[[OR (if uncertain): Jorgewich-Cohen: Sea turtles,]]For example, when in the nest, the hatchlings begin to vocalize from within the egg to synchronize hatching. And even if they all come out, individually they have less chance of being eaten by another animal. And in the case of the Amazon tortoise, the females wait for them when they go into the water, and they talk too. And they find each other, and then together they hike up the river into the forest.

Amer: A previous study published in 2020 by University of Arizona researchers concluded that only two out of 14 turtle families vocalized. Acoustic communication has also been found to have evolved independently in most large groups of tetrapods, originating between 100 and 200 million years ago. But now we know that is not the case.

Jorgewich-Cohen: I was very surprised – happily surprised – to find so many different types of sounds. And I took in more and more animals. And every animal I recorded made noises; I haven’t had any negative results. And that in itself was surprising.

Amer: Jorgewich-Cohen captured hundreds of hours of footage over two years—not just of turtles, but of lungfish, tuatara, and other creatures. Animals typically produce sounds for many reasons: to define a territory, to attract a mate, or to communicate with their young. It’s a useful skill.

Jorgewich-Cohen: I’ve found that in many turtle species there are sounds that are made only by males, some only by females, some only by juveniles, and some only by males when they are in front of the female.

Amer: If there’s one animal from this study that I would swear is 100 percent mute, it’s the Caecilian. For those who don’t know, let me paint a little picture: Caecilians are slippery, slimy, and slippery little things. They burrow and look like earthworms or even snakes. But neither are they. They are actually amphibians. They have a backbone and a skull, jaws and all, but no limbs. And like many tetrapods, they emit sounds through their airways, just like their common ancestor. It’s actually not that easy to meet one.

Jorgewich-Cohen: The Caecilian was special because I definitely didn’t expect it to make any noise. And not only does it do that, it makes very strange and very loud noises.

[CLIP: Audio of caecilain]

Amer: Not being crass, but that sounds a bit like a fart.

Jorgewich-Cohen: When I first heard it, I started laughing and I sent it to my friends who were doing field research with me. They also started laughing and said, “I can’t believe you. You made the noise with your mouth and send me the file.” I said, “No, I swear.”

Amer: The study “Common Evolutionary Origin of Acoustic Communication in Choanate Vertebrates” focuses less on the function of these sounds and more on the evolution of acoustic signals. But in future studies, the researchers plan to dig deeper, further analyzing the sounds to understand what they mean.

Jorgewich-Cohen: We also try to take recordings of the animals while we’re recording the sounds, so we can try to relate each type of behavior to the sounds they’re making and try to understand how they do it Use sounds or convey what ideas they have.

Amer: Sometimes Jorgewich-Cohen and his colleagues found more than 30 different sounds in a single species’ repertoire. The more socialized the animal is, the more diverse it seems to be, he says. But further studies are needed to confirm this.

Jorgewich-Cohen: Hopefully this is the start of a new field of study. So people will go out there and try to pick up more of these animals and come to new conclusions and new discoveries. But it would be really cool if we could do playback experiments, for example, and try to understand if they respond to the sounds we make. And then we can start to understand what these sounds mean and how they are used.

Amer: Thanks for listening! For Scientific American’s 60 Second Science, I’m Pakinam Amer.