There is croaking, chirping - and speaking: When the basic concept of acoustic communication emerged in the evolutionary history of land vertebrates, a study now sheds light on it: Researchers have found vocalizations in some animals previously thought to be mute and have classified this new information in the family tree of life. It became apparent that the basic abilities for acoustic communication did not arise several times in parallel, but rather go back to common ancestors of land vertebrates and lungfish, which existed more than 400 million years ago.
Many animals can hardly be overheard, but acoustic communication is much more widespread than one might think: while some are actually considered to be mute, many reptiles, amphibians and other vertebrates, which appear to be rather quiet, do make noises in certain situations. The acoustic signals play different roles: They can be used to find a partner, parental care or as a warning signal. Despite their importance, however, little is known about when and at what stage in evolutionary history these concepts first appeared in the so-called Choanata. In addition to land vertebrates, this term also includes representatives of lungfish.
When did the first sound?
There are two possible explanations for the evolutionary origins of sound communication among the Choanata: On the one hand, parallel developments seem possible. The partly clear differences between the structures of the hearing apparatus and the vocal tract are regarded as an indication that acoustic communication has developed repeatedly and independently in different animal groups. The alternative hypothesis, on the other hand, states that acoustic communication has an ancient common origin. This is supported by some morphological and neuronal similarities and also by the fact that among the Choanata the pulmonary respiratory system is always the physical source for the different sound production concepts.
One reason for the previously unclear picture of the evolutionary history was that information about vocal communication was missing in some key animal groups, say the scientists working with Gabriel Jorgewich-Cohen from the University of Zurich. Comparative analyzes therefore did not reveal any clear indications of the evolutionary roots of acoustic communication. That is why the team has now created new data bases. They specifically listened to animal species that had never been examined acoustically before. By recording the sounds and information on the respective behavior of 53 species, the researchers have now been able to decisively enrich the knowledge of the Choanata's vocal communication abilities. These animals belonged to the groups of tortoises, tuatara, creeping amphibians and lungfish. The team also conducted a search of the scientific literature to systematically identify other animal species across the spectrum that were found to be vocalizing.
Originating over 400 million years ago
The investigations revealed: "We were able to further clarify that acoustic communication is not only widespread in terrestrial vertebrates, but also demonstrate such abilities in several groups that were previously considered non-vocal," says Jorgewich-Cohen. Among other things, many turtle species previously thought to be mute actually have a broad and complex acoustic repertoire, the scientists report.
To draw clues to the evolutionary origin based on the new information, the researchers combined the collected data on the vocalization abilities of vertebrate species with methods for reconstructing the phylogenetic development. Combined with data from groups known to communicate acoustically, such as mammals, birds and frogs, the scientists were now able to map the phylogenetic tree of acoustic communication more clearly than previously.
As they report, the results now make the previously suspected multiple origin seem rather implausible: "Our results indicate that acoustic communication has not developed repeatedly in different vertebrate groups, but has a common and ancient evolutionary origin," says senior author Marcelo Sánchez-Villagra from the University of Zurich. "Our reconstructions show that this trait is at least as old as the last common ancestor of the Choanata, which lived about 407 million years ago," the scientists write.
Source: University of Zurich, specialist article: Nature Communications, doi: 10.1038/s41593-022-01177-4