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Wednesday, October 26, 2022
In findings published Tuesday in Nature Communications, scientists from the University of Zurich say that the first organisms to communicate vocally—by making sounds out of the air they breathe—did so in the Devonian period, over 407 million years ago. Their findings also support the idea that the act of using sound to communicate evolved just once.
Unlike previous studies, which hypothesized that sound-based communication evolved multiple times, this work concluded that vocal communication originated with the common ancestor of all choanate vertebrates, which include all vertebrates with lungs and nostrils. In other words, if it breathes, say these scientists, then it has a voice.
The researchers made recordings of 53 separate species, 50 of them turtles, which were previously thought to be the shelled silent type. They placed the animals in plastic pools to capture all sound. The team videoed and recorded specimens for at least 24 hours per species. They studied animals alone, in same-sex groups, in mixed-sex groups, and in groups containing individuals of different ages. This produced over 1000 hours of recorded sound to process. They concluded “a complex repertoire of sounds entails communicative meaning,” or that any animal capable of making many different sounds was therefore using sound to communicate. They then searched Google Scholar and Web of Science for other studies that covered songs, calls, and vocalizations and compiled the results.
“We were able to reconstruct acoustic communication as a shared trait among these animals, which is at least as old as their last common ancestor that lived approximately 407 million years before present,” said lead author Marcelo Sánchez.
Previous studies focused on animals known for the noises they make, such as frogs and crocodiles. By specifically including “species considered nonvocal,” such as turtles, lungfish, wormlike amphibians called caecilians, and tuatara, which are lizard-like reptiles native to New Zealand, these researchers were able to find that not only did these animals use sound to communicate after all, but the process had a certain universality: Although not all of the sound-making structures had the same tissue origin—birds’ voiceboxes do not come from the same embryological tissue as the mammalian larynx, even though both groups are famously loudmouthed—they all used air from the lungs to produce noise. Also significant, the motor neurons controlling the sound apparatus all originated in the same part of the brain, the caudal hindbrain. And every single beast was capable of hissing.
While the study generated data that many other biologists found impressive—the South American wood turtle was found to have a repertoire of more than 30 different sounds—there were some limitations. As evolutionary biologist John Wiens of the University of Arizona pointed out, the Zurich team did not establish that the animals were in fact using those sounds to communicate. The Zurich team plans to conduct further investigations to address this issue and collect more data on vocal communication in animals.