‘Chatty Turtles’ Flip the Script on the Evolutionary Origins of Vocalization in Animals

‘Chatty Turtles’ Flip the Script on the Evolutionary Origins of Vocalization in Animals
Closeup view of a turtle with its mouth open in the jungle near Coroico, Bolivia. Credit: Panther Media GmbH / Alamy Stock Photo

Recordings of more than 50 species of turtles and other animals help scientists reassess the origins of acoustic communication in vertebrates.

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

Clicks, clucks, grunts, and snorts–these are not sounds that we typically associate with turtles.

[CLIP: Audio of South American juvenile turtles]

Amer: They’re actually thought to be very quiet or even silent. It seems that we may have underestimated the amount of sound they can make. Now a new study in Nature Communications has collected vocal recordings from 53 species of turtles and other animals that were otherwise considered to be mute.

[CLIP: Audio of South American juvenile turtles]

Amer: Those clicks you’ve just heard were calls made by baby giant Amazon River turtles 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 started vocalizing more than 400 million years ago. (And just in case you aren’t familiar, tetrapods are four-limbed vertebrates that include amphibians, mammals, birds, and reptiles.) That’s at least 100 million years earlier than previous studies had 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 that published one of these first papers showing that turtles can communicate acoustically, and that inspired me. I returned home and bought some equipment so I could start recording my pets. I was surprised to discover that they also produced sounds, which I didn’t know existed for the species I had. I thought maybe they do. So I went out and recorded as many as possible [laughs].

Amer: That was Gabriel Jorgewich-Cohen, a researcher at the University of Zurich and study co-author. He is referring to Giant Amazon River turtles, also known as red-eared sliders in the US.

Jorgewich-Cohen: This is the only species known to have post-hatch parental care among all turtles, which is pretty amazing. They recorded the sounds of the animal to find out how it sounds. They also have a lower chance of being eaten individually when they are all out together. The Amazon River turtle is an example of this. When they go to the river, the females are waiting for them. They also vocalize. They find each other and then they move together up the river to reach the forest.

Amer: A previous study published in 2020 by researchers at the University of Arizona concluded that only two of 14 families of turtles vocalized. It also stated that acoustic communication evolved independently in most major tetrapod groups, with origins in the range of 100 million to 200 million years ago. We now know that this is not true.

Jorgewich-Cohen: I was very surprised–happily surprised–when I found so many different types of sounds. I kept recording more animals. Every animal I recorded made sound; I didn’t get any negative results. That was quite amazing.

Amer: Jorgewich-Cohen recorded hundreds of hours’ worth of footage over two years–not just of turtles but also of lungfish, tuatara and other creatures. Animals produce sounds for many reasons. It’s a useful skill.

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

Amer: If there’s one animal from this study that I would’ve sworn is 100 percent mute, it’s the caecilian. Let me give you a brief overview: Caecilians look slimy, slippery, and slithery. They burrow and look like earthworms, or even snakes. They are neither. They are actually amphibians. They have a skull and a backbone, with jaws and all, but no legs. They emit sounds through the respiratory tract, much like many tetrapods. It is not easy to find one.

Jorgewich-Cohen: The caecilian was a special one because I definitely expected it not to make any sounds. It makes strange and loud sounds, which is not surprising.

[CLIP: Audio of caecilain]

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

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

Amer: The study, “Common Evolutionary Origin of Acoustic Communication in Choanate Vertebrates,” is less focused on the function of these sounds, and more on the evolution of acoustic signals. The researchers will continue to analyze the sounds in order to better understand their meaning in future studies.

Jorgewich-Cohen: We try to also make footage of the animals while we’re recording the sounds so we could try to correlate any type of behavior to the sound that they were making and try to understand how they use the sounds or what ideas they convey.

Amer: Sometimes Jorgewich-Cohen and his colleagues would find more than 30 different sounds in a single species’ repertoire. He says that animals with more socialization are more vocally diverse. However, further research is needed to confirm this.

Jorgewich-Cohen: Hopefully this is the beginning of a new field of study. People will go out and record more animals to make new discoveries and draw new conclusions. It would be great if we could do playback experiments to see if the animals respond to our sounds. Then we can understand what these sounds mean and how to use them.

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

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