Social bias affects vigilance contagion in Japanese macaques

Yawn Contagion and Modality-Matching in the Female-Bonded Society of Geladas (Theropithecus gelada)

Behavioral contagion is widespread in primates, with yawn contagion (YC) being a well-known example. Often associated with ingroup dynamics and synchronization, the possible functions and evolutionary pathways of YC remain subjects of active debate. Among nonhuman animals, geladas (Theropithecus gelada) are the only species known to occasionally emit a distinct vocalization while yawning. Yet, the role of different sensory modalities in YC remains poorly understood. Due to their social and communicative complexity, geladas serve as an excellent model for investigating the effects of multimodality and social factors on behavioral contagion. Here we studied a large zoo-housed colony of geladas (103 subjects, 1422 yawns) and confirm the previous evidence for visual and auditory YC. Hearing, seeing, or hearing and seeing yawns significantly triggered contagious yawning at comparable levels. Additionally, we found no evidence of laterality influencing responses based on the side of detection. While the social bond, measured via grooming, between the trigger and receiver did not correlate with YC, a consistent sex effect emerged. Females responded more frequently to female than to male yawns and were more likely to match modality (i.e., vocalized vs. nonvocalized) and mirror morphology of other females' yawns. Effective female-female communication and affiliation are crucial for maintaining cohesion and fostering strong intra-unit relationships among geladas. Our results underscore the importance of different sensory components in the distribution of YC, particularly for species living in complex social systems. These findings raise further questions about the functional and emotional significance of yawning and potential inter-sexual differences, suggesting that the phenomenon is more complex than previously thought.

First predict, then bond: Rethinking the function of mimicry from prediction to affiliation in human and non-human animals

Automatic mimicry, where social animals mimic the emotional expressions of others, is a well-documented phenomenon. While research has extensively examined how being mimicked influences our perception of others, the fundamental question of why we mimic remains largely unexplored. Previous theories often link mimicry with an affiliative social goal. While we agree that mimicry can increase survival chances by enhancing group cohesion, we argue for a more primitive adaptive value that may operate independently of social bonding. By reviewing existing literature, we propose that mimicry serves as a mechanism to predict other individuals, and consequently, the environment, enhancing survival of the individual. We posit a shift towards understanding mimicry as a mechanism that minimizes prediction error, empowering individuals to navigate their surroundings more effectively. Embracing mimicry as a tool for self-preservation and environmental prediction opens new avenues for interdisciplinary research in comparative psychology and behavioral ecology.

Familiarity modulates both intra- and interspecific yawn contagion in red-capped mangabeys

Yawn contagion (YC) is, compared to spontaneous yawning, an evolutionary recent phenomenon probably linked to behavioral synchronization in highly social species that is more likely when it involves familiar subjects. Here, we investigate for the first time in monkeys which factors modulate intra- and interspecific YC. Through an experimental approach, we exposed 17 red-capped mangabeys to video stimuli (Yawn vs Control) depicting familiar/unfamiliar red-capped mangabeys and humans, and unfamiliar hamadryas. We found that mangabeys yawned more often in response to Yawn than Control videos independently from the species depicted, demonstrating both intra- and interspecific YC in the tested species. Moreover, both mangabey and human familiar yawning stimuli evoked a stronger yawning response in the subjects compared to the unfamiliar counterparts. Neither the amount of time spent looking frontally at the screen (probability of stimulus perception) nor the levels of self-directed behaviors (a proxy of anxiety) accounted for the results. In conclusion, we provide the first evidence that in non-human primate familiarity modulates both intra- and inter-specific YC. Stimuli emitted by familiar faces somehow ease the mechanisms underlying YC, and this modulation can also apply to heterospecific subjects when previous shared experiences provide the prerequisites for the development of social bonds.