Low relationship quality predicts scratch contagion during tense situations in orangutans (Pongo pygmaeus)

Abstract

Primates show various forms of behavioral contagion that are stronger between kin and friends. As a result, behavioral contagion is thought to promote group coordination, social cohesion, and possibly state matching. Aside from contagious yawning, little is known about the contagious effect of other behaviors. Scratching is commonly observed during arousal and as such may play a role within group dynamics. While the Bornean orangutan ( Pongo pygmaeus ) is commonly considered the least social great ape, orangutans do engage in social interactions. Therefore, their social organization makes them a suitable case for studying the social function of behavioral contagion. Through behavioral observations of captive orangutans, we recorded all yawn and scratch events together with the corresponding behavior of all bystander group‐members. As yawning was rarely observed, no conclusions could be drawn regarding this behavior. Scratching was contagious and occurred within 90 s after the triggering scratch. Specifically, orangutans showed increased scratch contagion when they had seen a weakly bonded individual scratch during tense contexts. When the orangutan had not seen the triggering scratch, the contagiousness of scratching was not affected by context or relationship quality. Our results indicate that behavioral contagion is not simply higher between individuals with stronger social relationships, but that the contagiousness of behaviors may vary based on the context and on social factors. We discuss these findings in light of an adaptive function that may reduce aggression.

Experimental evidence for yawn contagion in orangutans (Pongo pygmaeus)

“…For instance, a large study in rats has shown a familiarity bias in the opposite direction with rats being more likely to yawn in response to unfamiliar yawns 23 . Similarly, a recent study investigating scratch contagion in orangutans found that during tense situations, orangutans are more likely to take over scratching from individuals with whom they have a weak bond 80 , indicating a (negative) correlation between social closeness and the contagiousness of a behavior or motor pattern. Thus, it remains possible that social modulation of CY is present in orangutans, at least in those living with conspecifics in captivity, although its presence was not shown in our sample.…”

“…For instance, related female orangutans are known to associate more often than unrelated females 78 , and prefer the long-calls of dominant males 79 . Additionally, in a recent study, orangutans were shown to scratch contagiously in response to conspecifics scratching, suggesting a potential case of emotion contagion 80 . Interestingly, scratch contagion was stronger between weakly bonded individuals during tense situations, which shows a social closeness bias in the opposite direction.…”

Physiological synchrony is associated with cooperative success in real-life interactions

“…Synchronization is observed on many different levels 9 , in infants 6,28 , and in different species 13,29,30 . Theoretically, it has been proposed to make two interaction partners more similar, aligned, and easier to predict, which is why they are able to cooperate more efficiently 16 .…”

Social contagion of affiliation in female macaques

“…The vast majority of studies on behavioural contagion focuses on non-interactive activities, such as contagious yawning and itching/scratching [ 13 , 14 ]. Contagious yawning is probably the best-studied example of non-interactive contagious behaviour and may serve to enhance collective vigilance and to facilitate an adaptive response to external stimuli [ 15 ].…”

“…The degree of behavioural contagion of non-interactive behaviour is often modulated by relationship quality between the stimulus individual and the bystander. Contagious yawning is enhanced when the triggering individual is a close social partner in geladas ( Theropithecus gelada ), bonobos ( Pan paniscus ) and humans ([ 40 ]; for an opposing effect in contagious scratching, see [ 14 , 21 , 41 ]) or an in-group versus out-group individual in chimpanzees [ 42 ]. Yawn contagion is also facilitated when the triggering individual is of high social status, i.e.…”