by Think of the most chatty creatures in the animal kingdom and songbirds, dolphins and, yes, humans probably come to mind. Turtles probably don’t register. But these charismatic reptiles also communicate through a wide repertoire of clicks, snorts and laughter. Now, by recording the “voices” of tortoises and other supposedly silent animals, scientists have concluded that all terrestrial vertebrate vocalizations, from the song of the canary to the roar of the lion, have a common root that goes back more than of 400 million years.
The findings imply that animals began to vocalize very early in their evolutionary history, even before they had well-developed ears, says W. Tecumseh Fitch, a bioacoustician at the University of Vienna who was not involved in the work. “It suggests that our ears evolved to hear these vocalizations.”
Several years ago, University of Arizona evolutionary ecologist John Wiens and his graduate student Zhuo Chen began investigating the evolutionary roots of acoustic communication, basically defined as the sounds that animals make with their mouths using their lungs. Combing through the scientific literature, the duo compiled a family tree of all known acoustic animals at the time, eventually concluding that such sound-producing abilities arose multiple times in vertebrates between 100 and 200 million years ago.
But Gabriel Jorgewich-Cohen, an evolutionary biologist at the University of Zürich, noticed an oversight: turtles. Although Wiens and Chen had discovered that only two of the 14 turtle families made sounds, he was finding many more. He spent 2 years recording 50 species of turtles in the act of “speaking”.
With microphones in hand, Jorgewich-Cohen and his colleagues had also discovered acoustic vocalizations in three other creatures not known to do so: a legless amphibian called cecilia; a New Zealand lizard-like reptile called a tuatara; and the lungfish, an air-breathing freshwater fish that is considered the closest living relative of land animals.
“They were really able to get some very unusual recordings from some very unusual species,” says Fitch, who studies the evolution of speech.
Of the 53 species recorded by Jorgewich-Cohen’s team, the star was the South American wood turtle (Rhinoclemmys punctularia), a fist-sized species that is sometimes sold as a pet. It emitted more than 30 vocalizations, including a door creak used exclusively by males courting females and a screech and cry produced only by young tortoises. In general, some sounds were associated with aggression, such as biting, while others seemed to be a way of greeting new people and were often accompanied by head movements.
By adding this previously unknown talk to existing data on acoustic communication, Jorgewich-Cohen and colleagues constructed a new, more complete evolutionary tree consisting of some 1,800 species. Each branch of this tree contained animals that made these sounds, they report today in nature communicationssuggesting that acoustic communication evolved only once in a common ancestor of land animals and lungfish approximately 407 million years ago.
“That is incredible!” says Elizabeth Derryberry, a behavioral ecologist at the University of Tennessee, Knoxville, who was not involved in the work. “It suggests that acoustic communication evolved in concert with the lungs.”
The work could help scientists trace the evolution of communication in our own species, adds Anthony Russell, an evolutionary biologist emeritus at the University of Calgary. But he expects the new findings to spark controversy. The researchers assume that other animals are listening and responding to the vocalizations they recorded in many of the quieter species, “but such an assumption is wild at best,” he says. It may be that no one pays attention to these noises.
Jorgewich-Cohen is already working on that problem. He is currently documenting how turtles and other calmer species use these sounds. He also wants to compare the sounds of terrestrial vertebrates and lungfish with those of other fish to see if the acoustic evolutionary tree extends even further back in time. “Do we share the ability to produce sound with some groups of fish?” he asks. “If so, the origins of acoustic communication must be much older than we suppose.”
