Motherhood and Sex Predict Emotional Reactivity During a Predator Confrontation in Two Macaque Species

Understanding how animal emotions influence behavior and physiology is essential to comprehend animals' emotional responses and how these may differ between individuals. However, accurately assessing animal emotions is challenging due to their multifaceted nature and the need for multimodal approaches. This study investigates the effect of maternal status (mothers vs. females without dependent offspring), sex, and species on the emotional reactivity of two macaque species (long-tailed and rhesus macaques) confronted with a threatening situation. Using a non-invasive and multidimensional approach, we collected data on their behavior, facial temperature changes, and vocal reactivity during a predator exposure. We show that mothers produced a stronger initial physiological response, that is, a decrease in the nose tip temperature, whereas males and non-mothers showed a stronger behavioral response, with an increase in stress-related behaviors 10 min after exposure. Vocal behavior, however, did not differ across groups or species. Long-tailed macaques had a stronger initial physiological response and showed more stress-related behaviors at the beginning of the experiment than rhesus, while rhesus macaques showed more stress-related behaviors at the end. While mothers showed a stronger internal physiological response, non-mothers and males may be in a position to afford stronger behavioral reactions. Long-tailed macaques seem to respond faster to threats than rhesus macaques, which is in line with them being more vulnerable to predators. In conclusion, our study shows that emotional responses to a potential danger differ across maternal status, sex, and species, and concurrently highlights the importance of a multidimensional approach when studying such differences.