From ribbits to roars, the animal kingdom is filled with weird and wonderful vocalizations – but why did they evolve? Turns out, among the vertebrates, sound production appeared between 100 and 200 million years ago, and its arrival was strongly linked to life in the dark.
Vertebrates are animals with backbones, encompassing five major groups – birds, fish, reptiles, amphibians, and mammals, which include us. A team from the University of Arizona and China’s Henan Normal University set out to investigate the evolution of acoustic communication in vertebrates of the land-dwelling variety, looking back as far as 350 million years.
They created a vast tree of life incorporating 1,800 species and noted whether each animal used sound to communicate or relied on other means. They then used statistical analysis to determine whether acoustic communication evolved separately in each group, and whether an absence of light might have played a role.
Reporting their findings in the journal Nature Communications, the team discovered that the common ancestor of vertebrates did not use vocal communication, meaning that different animal groups must have evolved to talk to each other using sound independently over the last 100-200 million years. Animals need to communicate to transmit all sorts of information, from trying to impress a potential mate to warning others of danger.
The researchers uncovered a connection between the evolution of acoustic communication and being nocturnal. After all, colors and body movements are no use for communication in the absence of light. However, what’s also interesting is that while darkness was needed for vocalizations to appear, they remained in animals that are now only active during the day. The researchers believe the dawn chorus created by musical songbirds may be a remnant of their ancestors’ nocturnal behavior.
"There appears to be an advantage to evolving acoustic communication when you're active at night, but no disadvantage when you switch to being active during the day," John J. Wiens of the University of Arizona said in a statement. "We have examples of acoustic communication being retained in groups of frogs and mammals that have become diurnal, even though both frogs and mammals started out being active by night hundreds of millions of years ago."
The team also concluded that the ability to vocalize did not drive speciation – the appearance of new species – within different animal groups, the opposite of what has long been thought true.
"If you look at a smaller scale, such as a few million years, and within certain groups like frogs and birds, the idea that acoustic communication drives speciation works out," Wiens said, "but here we look at 350 million years of evolution, and acoustic communication doesn't appear to explain the patterns of species diversity that we see."
Birds and crocodilians both use acoustic communication, but there are many thousands of bird species and only 25 crocs. Snakes and lizards are pretty quiet critters, but comprise 10,000 species. The incredibly vocal mammals, meanwhile, include just 6,000 species. So, it seems there is no obvious link between the number of new species that have appeared over time and the ability to screech, chatter, or howl.
The researchers say their findings highlight the importance of an animal’s surroundings in influencing the evolution of new abilities and behaviors, and that millions of years of being exposed to different ecological factors has shaped the species we share our planet with today.