Affective Responses and Behavioral Strategies to Social Fusion Events in Zoo-Housed Bonobos

Species with fission-fusion dynamics may face heightened social tension during fusion events due to relationship insecurity and competition over resources. Affective consequences of such events are important determinants for behavioral responses, yet remain poorly understood. To evaluate the affective consequences of fusion events, we studied cognitive bias responses and changes in the behavior of zoo-housed bonobos following managed fission-fusion dynamics. Eight bonobos completed a response slowing task on touchscreens, in which individuals with negative affect show longer reaction times to targets when a mildly threatening stimulus is displayed. We tested the bonobos on days before, during, and after fusion events and simultaneously observed their behavior. Agonistic and socio-sexual behaviors increased during fusions. The bonobos also showed response slowing during trials with mildly threatening stimuli during fusion events, suggesting a shift towards negative affect. Response slowing effects were short and returned to baseline levels on days after the fusion events. Post hoc analyses furthermore showed arousal-related response speeding during control trials. Independent of testing condition, response slowing was negatively associated with socio-sexual behavior, and positively associated with social play behavior, highlighting affective correlates of these behaviors. Our findings provide insights into the affective responses to fusion events in bonobos, suggesting brief shifts towards negative affect. Nonetheless, changes in behavioral patterns, and cognitive correlates of affective states, presumably function to limit the escalation of conflict and facilitate successful fusions.