Searching for a common ancestor of not-so-dumb turtles

published on Tuesday, October 25, 2022 at 5:18 p.m.

More than 50 animal species thought to be mute, including turtles, actually have some form of vocal expression, according to a study released Tuesday that suggests the feature dates back to a common ancestor more than 100 years ago. 400 million years old.

It all started during a research trip on turtles in the Amazon rainforest led by evolutionary biologist Gabriel Jorgewich-Cohen, explained to AFP by this first author of the study.

“When I got home, I decided to register my own animals,” including Homer, a turtle he had owned since he was a child. Having discovered that they expressed vocal sounds, he recorded those of other species of turtles, using a hydrophone if necessary to pick up their vocalizations in the water.

“All the species that I recorded produced sounds (…) and we then wondered how many other animals known to be dumb produced sounds”, continues Gabriel Jorgewich-Cohen, researcher at the University of Zurich.

The study published in Nature Communications identifies fifty species of turtles as well as those of three “very strange animals” known to be mute. Including the “Lungfish” (a kind of fish called dipneuste in French, equipped with a lung in addition to its gills), and the Cécilies, amphibians having the shape of worms.

The team even recorded the sons of a rare species of reptile found only in New Zealand, the Tuatara, the sole survivor of an order that colonized the globe.

All of these animals produce vocal sounds such as a click, chirp or tonal sound, even at rest or just a few times a day, according to the study.

– “From the same place” –

The researchers combined their findings with data on the evolutionary history of acoustic communications from 1,800 other animal species. They then used a technique called ancestral reconstruction, which calculates the probability of a characteristic common to several species in the past.

“We found that the common ancestor of this group already produced sounds and intentionally communicated using these sounds,” says the researcher.

Scientists until now thought that tetrapods – four-legged animals including turtles – and lungfish evolved separately into forms of vocal communication. “But we now show the opposite, they come from the same place”, explains the researcher.

This common ancestor lived at least 407 million years ago, during the Paleozoic era, according to the study.

The idea that “acoustic communication arose in a common ancestor of lungfish and tetrapods is interesting and surprising,” reports John Wiens, professor of evolutionary biology at the American University of Arizona, to AFP.

But according to him, the authors of the study did not “necessarily make the distinction between what is the production of sounds by animals and what is acoustic communication”.

Yet, as the study’s lead author explains, the researchers compared the animals’ audio and video recordings to check how well they matched given behaviors. To ensure that “those wires are actually used for communication”, said Gabriel Jorgewich-Cohen.

Pr. Wiens, who published in 2020 a study on the origins of acoustic communication in the obtained, welcomed these new data concerning new species, while calling for “more advanced analyzes”.

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