Oxytocin regulates consensus assessment in zebrafish social decision-making

Group-living animals can gain information from conspecifics and integrate it in behavioural decisions that increase their survival. Social information value depends on two key dimensions: salience, the perceptual prominence of social signals, and conformity, the tendency to follow the majority based on the appraisal of signal consensus amongst conspecifics. Here we tested the effects of oxytocin, a neuromodulator conserved across vertebrates, on salience and conformity processing of conspecific alarm behaviours, using zebrafish oxytocin-receptor ( oxtr −/− ) knockout mutants. We employed video-playback treatments to independently manipulate the absolute number (salience) and relative proportion (consensus) of alarm signals against matched neutral controls. Knocking out oxtr eliminated increased attention to higher signal salience observed in wild-type siblings but did not alter behavioural responses. In contrast, receptor loss abolished conformity to majority alarm signals, eliminating consensus-dependent increases in social contagion and subsequent social approach. Predictive models further revealed that oxytocin enables feedback from immediate social responses to shape later decisions, specifically when social information is corroborated by the majority. These findings challenge the prevailing view that oxytocin primarily enhances social salience, expanding its role to the assessment of consensus to implement conformity decisions, representing a foundational process in vertebrate social decision-making.