Page 116 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Chapter 5
Wilkinson et al., 2011). This illustrates the ongoing debate on the possible mechanism underlying contagious yawning.
Although not receiving as much attention as contagious yawning, self- scratching may be another interesting behavior for contagion studies. Self-scratching is commonly associated with the presence of psychological and physiological stress (Maestripieri et al., 1992; Schino et al., 1991; Troisi, 1999). For example, increased self- scratch rates have been reported during aggressive interactions (Palagi & Norscia, 2011), post-conflict interactions without reconciliation (reviewed in Aureli et al., 2002), dominance‐related interactions (Kaburu et al., 2012; Peignot et al., 2004), and predation attempts (Palagi & Norscia, 2011). Concurrently, self-scratching behavior is reduced after play bouts (Norscia & Palagi, 2011b), during affiliative interactions (Aureli & Yates, 2010), and after reconciliation following aggressive interactions (Aureli et al., 1989). However, a recent study also found that self-scratching increases with positive arousal (e.g., during play bouts), suggesting that it may be a marker of general emotional arousal, rather than an indicator of negative emotions specifically (Neal & Caine, 2016).
Apart from benefits for the expresser (Koolhaas et al., 1999), self-scratching potentially signals arousal to other group‐members (Bradshaw, 1993). In rhesus macaques (Macaca mulatta), for example, self-scratching reduces the likelihood of subsequent aggression and increases the chance of affiliative interactions (Whitehouse et al., 2017). Furthermore, stressed individuals are a potential threat to group‐members as they tend to behave unpredictably (Aureli et al., 1992). As such, the recognition and acquisition of the emotions of aroused individuals can result in fewer costly interactions (Whitehouse et al., 2016). While these studies suggest that self-scratching may play an important role within social groups, the contagious effect of self-scratching and its potential function is poorly understood.
Most studies on mimicry in great apes focused on bonobos and chimpanzees, probably because of their complex social structures, advanced cognitive capacities, and evolutionary proximity to humans (Maclean, 2016). However, the orangutan too, is one of our closest living relatives with highly developed cognitive skills (Damerius et al., 2019; Van Schaik et al., 2003), yet is considered semi‐solitary as it does not live in stable social groups (Delgado & Van Schaik, 2000; Galdikas, 1985; Mitra Setia et al., 2009; Singleton et al., 2009; Van Schaik, 1999). Nonetheless, orangutans still form temporary parties for social reasons, e.g., for mating opportunities, protection from male coercion, and socialization opportunities for infants (Mitani et al., 1991; Mitra Setia et al., 2009; Singleton et al., 2009; Van Schaik, 1999). Furthermore, zoo‐housed
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