Call patterns encode and transmit emotion in marmoset monkeys

Marmoset monkeys have attracted much attention as a non-human primate model for studying vocal communication, but the call pattern and its meaning in marmoset communication are largely unknown. Here, we analyze sounds produced by hundreds of marmosets either in isolation or in pairs and reveal distinct call patterns in marmoset communication. The most prominent phee calls could be categorized into multiple grades based on the number of comprising phee syllables. Call transitions exhibited non-random patterns, favoring transition to the same or adjacent grade, with long sequences limited within two adjacent grades. The interval, composition, and temporal distribution of calls were significantly different between isolated and paired marmosets. Notably, different patterns of phee calls correlated with the heart rates and emotional states of marmoset, with the higher call grade reflecting a more agitated state. Antiphonal calling also exhibited distinct patterns and phee calls directly affected the heart rate of the listener in a manner depending on the grade of phee calls. Thus, phee call patterns in marmosets could encode emotional states and transmit emotion between turn-taking marmosets. How emotional expression in animals evolves into semantic communication in humans remains a mystery. Such complex call patterns in marmoset vocalization could represent the evolutionary prelude to semantic communication in primates.