Oxytocinergic Signaling Promotes Partner-directed Prosocial Choice in a Biparental Cichlid Fish

Humans display prosocial behavior across various contexts. Elucidating the origins of the proactive prosociality that characterizes humans has been a longstanding objective in evolutionary biology. In this study, we investigated whether the proximate mechanisms underlying prosociality are evolutionarily conserved by examining the role of oxytocin, a known regulator of prosocial behavior in mammals, in the convict cichlid Amatitlania nigrofasciata, a monogamous fish species exhibiting biparental care. To this end, we employed a prosocial choice task—an experimental paradigm in which the subject selects between an antisocial choice, where only the subject receives a reward, and a prosocial choice, where both the subject and its experimental partner receive rewards. Our findings revealed that in the group that did not receive oxytocin receptor antagonists (ORAs), male subjects learned to prefer the prosocial choice, allowing both themselves and their female reproductive partners to receive food rewards. However, when treated with ORAs, the male subjects exhibited a reduced preference for prosocial choices. These clear and compelling findings provide strong evidence supporting the evolutionarily conserved role of oxytocin as a key regulator of fundamental prosocial behaviors across vertebrates.