The 35 million-year-old adaptation that helps lemurs sound bigger than they are

Researchers have discovered that lemurs are capable of exaggerating their size thanks to the unique structure of their larynx.

Different species of lemur all possess an additional pair of vocal folds - an anatomical feature unlike any other primate, they revealed.

The study, published in the journal Scientific Reports, involved carrying out CT scans of the larynges of different species of lemurs and constructing a silicone model to recreate and test the acoustic properties of these additional vocal folds.

Co-author Dr Jacob Dunn, associate professor in evolutionary biology at Anglia Ruskin University (ARU), said: “All primates have a pair of vocal folds in their larynx, which vibrate to modify the air flow, and our research shows that all species of Madagascan lemurs have a unique additional pair of folds in the vestibular region, parallel to the vocal folds.

“This is likely to have developed because ancestors possessing these twin vocal folds may have had a selective advantage compared with members of the same species without this adaptation.

“We think these twin vocal folds serve to not only increase the complexity of their calls but crucially may also help a lemur exaggerate its body size, which would have significant benefits when competing for territory or mates.”

The researchers, led by colleagues from Kyoto University in Japan, studied the larynges from two families of lemurs – Lemuridae, which include the ring-tailed lemur (Lemur catta) and black-and-white ruffed lemur (Varecia variegata), and Cheirogaleidae lemurs, such as the grey mouse lemur (Microcebus murinus). They found both families possess these unique vestibular vocal folds, a novel evolutionary adaptation probably acquired by their common ancestor at least 35 million years ago.

They allow lemurs to make a wider variety of calls while making vocalisation more efficient, meaning they expend less energy communicating over distances.

The silicon model also showed the additional vocal folds lower the frequency of sounds produced, making a lemur sound larger.

Senior author Professor Takeshi Nishimura, of the Center for the Evolutionary Origins of Human Behavior at Kyoto University, said: “Primates use varied vocal repertoires to communicate, and the larynx plays a key role in generating these calls.

“By recreating the lemurs’ unique vocal structure through our model and studying its oscillation properties, we found that simultaneous vibrations of the twin pairs of vocal folds lowers the frequency of the calls produced – helping the lemur sound larger than it is – and also serves to improve vocal efficiency.”

The full open access study, published in the journal Scientific Reports, is available here: https://www.nature.com/articles/s41598-024-54172-z