Oxytocin increases during fur‐rubbing regardless of level of social contact in tufted capuchin monkeys

Abstract

Social interactions induce oxytocin release in many social species, suggesting that oxytocin is a critical part of social bonding among individuals. However, oxytocin also increases as a result of physical contact and stimulation, making it unclear which features of affiliative behaviors (for instance, social interaction or physical contact with a conspecific) drive the oxytocin increase observed after engaging in these behaviors. We attempted to tease this apart by studying the differential effect of social interaction, visual coordination with a conspecific, and physical stimulation during the fur‐rubbing behavior of tufted capuchin monkeys (Sapajus [Cebus] apella), which often involves social contact with groupmates but is in some cases performed alone. We induced fur‐rubbing by providing onions under three conditions: when capuchins had physical access to their social group and fur‐rubbed in contact with groupmates (social condition), when capuchins were separated from their social group but could still see them fur‐rub (visual coordination), and when capuchins were physically and visually separated from their groupmates (physical stimulation only). We assessed urinary oxytocin in these three conditions and compared them to a control condition in which apples were provided and no fur‐rubbing was observed. Capuchins fur‐rubbed for less time when they could not see their groupmates, but fur‐rubbing increased urinary oxytocin above the control condition in all three fur‐rubbing conditions equally, suggesting that the physical stimulation derived from fur‐rubbing was the most important driver of oxytocin increase. These results support a model in which physical stimulation is an important factor in the relationship between oxytocin and at least some behaviors, suggesting that oxytocin increase alone is not necessarily indicative of a social influence on behavior. Future work is needed to determine the contexts in which social factors do impact oxytocin, and whether the downstream behaviors are the same for socially and nonsocially induced oxytocin release.

No evidence of attentional bias toward threatening conspecific and allospecific faces in capuchin monkeys (Sapajus [Cebus] apella) using a dot-probe task.

“…Bouts of fur-rubbing can be induced by providing capuchins with specific plant foods (alliums, such as onions, or peppers) and this behavior ultimately increases levels of urinary OT between 15- and 60-min post-fur-rubbing bout in capuchins (Benítez et al, 2018). Fur-rubbing is not reliant on social interaction and OT increases even when individuals fur-rub alone (Sosnowski et al, 2023). Thus, one of the goals of this research was to compare capuchins’ attentional biases after both exogenous administration and endogenous induction to determine if OT influences behavioral responses to threatening stimuli, and to determine whether there was a difference between the two methods of administration on subsequent behavioral response to a dot-probe task.…”

Conserved and differing functions of the endocrine system across different social systems – oxytocin as a case study

“…Further, some of these gregarious species are highly curious, manipulative, and cooperative in a laboratory setting, which provides the opportunity for controlled study of hormonal correlates of behavior and subsequent decision-making. As an example of one such species, capuchin monkeys ( Sapajus apella ) show a reliable increase in oxytocin following grooming and following fur-rubbing, a behavior often done in concert with conspecifics, indicating that these behaviors are serving as a bond maintenance behavior even among non-kin dyads ( 26 , 27 ). Further, as some captive capuchins are trained to complete cognitive tasks, they represent a unique opportunity to manipulate endogenous oxytocin and study subsequent changes in social attention and behavior ( 28 ).…”