Abstract
In primates, yawn contagion (the yawning response elicited by others' yawn) is variably influenced by individual (e.g., sex, age) and social factors (e.g., familiarity) and possibly linked to interindividual synchronization, coordination, and emotional contagion. Two out of three studies on yawn contagion in bonobos (Pan paniscus), found the presence of the phenomenon with mixed results concerning the effect of familiarity and no replication on its modulating factors. To address this puzzling issue, we recorded all occurrences data on yawn contagion in a captive bonobo group (March–June 2021; 18 individuals; La Vallée des Singes, France). Contrary to chimpanzees and humans, the number of triggering yawns increased contagion, possibly owing to a higher stimulus threshold. This aspect may explain the interindividual variability observed in yawn contagion rates. In subjects under weaning, we did not detect yawn contagion and, as it occurs in certain human cohorts, yawn contagion declined with age, possibly due to reduced sensitivity to others. Females responded more than males and elicited more responses from females when showing sexual swelling. As reproductive females are central in bonobo society, our results support the hypothesis that—as in other Hominini—the most influential sex can influence yawn contagion. The relationship quality (measured via grooming/play) did not affect yawn contagion, possibly due to bonobos' xenophilic nature. Overall, this study confirms the presence of yawn contagion in bonobos and introduces new elements on its modulating factors, pointing toward the necessity of cross‐group studies.
Highlights
While spontaneous yawning is not dependent on the detection of others' yawns, contagious yawning occurs when the yawn emitted by an individual works as a releasing stimulus and induces yawning in another individual (Provine, 1989)
Prediction 3: Individual and social factors—In the Hominini, the trigger's rank and sex can have an influence on yawn contagion rates, with individuals responding mostly to men in certain cohorts of humans and chimpanzees and to females in bonobos (Demuru & Palagi, 2012)
In our case we identified two conditions: (1) Post‐Yawning (PY)—after the last triggering yawn a potential responder was observed in a 3‐min time window to record whether and when there was a yawning response; (2) Matched Control (MC)—at the same time (±1 h) as the PY in the first suitable day, under similar social and environmental conditions and in the absence of any previous triggering yawn, the same potential responder was observed for three minutes to check whether and when yawning occurred
Summary
While spontaneous yawning is not dependent on the detection of others' yawns, contagious yawning occurs when the yawn emitted by an individual (hereafter trigger) works as a releasing stimulus (sensu Tinbergen & Perdeck, 1950) and induces yawning in another individual (hereafter responder) (Provine, 1989). Prediction 3: Individual and social factors—In the Hominini, the trigger's rank and sex can have an influence on yawn contagion rates, with individuals responding mostly to men in certain cohorts of humans (for yawns that are heard but not seen; Norscia et al, 2020) and chimpanzees (dominant males especially; Massen & Gallup, 2017) and to females in bonobos (Demuru & Palagi, 2012). Owing to the phylogenetic closeness of bonobos to humans and chimpanzees (Prüfer et al, 2012), we expected that age might have a similar effect on yawn contagion in our study group (Prediction 3b). We expected to find a positive effect of familiarity on yawn contagion in our bonobo group, observed under naturalistic conditions (Prediction 3c)
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