‘Chatty Turtles’ flips the script on the evolutionary origins of vocalization in animals

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

Clicks, clucks, grunts and snorts: these are not sounds we normally associate with turtles.

[CLIP: Audio of South American juvenile turtles]

Amer: In reality, they are believed to be very quiet or even silent. But it seems we’ve vastly underestimated the amount of sound they can produce. Now a new study in Nature Communications has compiled vocal recordings from 53 species of turtles and other animals otherwise considered mute.

[CLIP: Audio of South American juvenile turtles]

Amer: Those clicks you just heard were calls made by baby giant Amazon river turtles swimming together. A group of evolutionary biologists and other scientists from five different countries studied these recordings and combined them with vocal repertoires of some 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 vocalizing more than 400 million years ago. (And 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 acoustic history of animals with backbones.

Gabriel Jorgewich-Cohen: I did fieldwork in the Brazilian Amazon with a researcher who published one of these early papers showing that turtles can communicate acoustically, and that inspired me. So I came home, got some equipment, and started filming my own pets. And I found that they also made sounds, and the species I had were not known to make sounds. So I started to think maybe everyone does, 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 the giant Amazon river turtles, better known as red-eared sliders in the United States.

Georgewich-Cohen: This is the only species known to have post-hatching parental care among all turtles, which is quite surprising. And they discovered it by recording the sounds of the animal, not only of this species but also of 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 also when they all go out together, individually they have less chance of being eaten by another animal. And in the case of the Amazon river turtle, when they go to the water, the females are there waiting for them, and they are also vocalizing. And they meet, and then they migrate together up the river into the forest.

Amer: An earlier study published in 2020 by researchers at the University of Arizona concluded that only two of 14 families of turtles vocalized. He also claimed that acoustic communication evolved independently in most major groups of tetrapods, with origins in the range of 100 million to 200 million years ago. But now we know that’s not the case.

Georgewich-Cohen: I was very surprised, happily surprised, when I found so many different types of sounds. And I kept recording more and more animals. And every animal I recorded made sounds; I had no negative results of any kind. And that was amazing in itself.

Amer: Jorgewich-Cohen recorded hundreds of hours of footage over two years, not only of turtles but also lungfish, tuataras and other creatures. Animals often make sounds for many reasons: to define territory, to attract a mate, or to communicate with their young. It is a useful skill.

Georgewich-Cohen: I found that for many species of turtles, there are sounds that only males make, there are some that only females make, and some only by juveniles, and some that males only make when in front of the female.

Amer: If there’s one animal in this study that I would have sworn was 100 percent mute, it’s the caecilian. For those unfamiliar, let me paint a little picture: Caecilians are slippery, slimy, slippery little things. They make burrows and look like earthworms or even snakes. But they are not. In fact, they are amphibians. They have a backbone and a skull and jaws and everything, but they don’t have any limbs. And like many tetrapods, they make sounds through their airways, just like their common ancestor. Actually, it is not very easy to find one.

Georgewich-Cohen: The cecilian was special because she definitely expected her not to make any sound. And it’s not just that it does, but it makes very strange and very loud sounds.

[CLIP: Audio of caecilain]

Amer: I don’t mean to be rude, but that sounds a bit like a fart.

Georgewich-Cohen: When I first heard it, I laughed and sent it to my friends who did the fieldwork with me. They also started laughing and said, “I can’t believe you. You made the sound with your mouth and you are sending me the file. I was like, “No, I swear.”

Amer: The study, “Common Evolutionary Origin of Acoustic Communication in Choanan 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 by analyzing the sounds in an attempt to understand what they mean.

Georgewich-Cohen: We also try to take shots of the animals while recording the sounds so that we can try to correlate any kind of behavior with the sound they were making and try to understand how they use the sounds or what ideas they convey.

Amer: Sometimes Jorgewich-Cohen and her colleagues found more than 30 different sounds in the repertoire of a single species. It seems that the more socialized the animal is, the more vocally diverse it is, she says. But more studies are needed to confirm this.

Georgewich-Cohen: Hopefully this is the beginning of a new field of study. So people are going to go out and try to record more of these animals and come to new conclusions and new discoveries. But it would be great if we could, for example, do reproduction experiments and try to understand if they respond to the sounds we make. And then we can begin 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.

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