Prosociality and reciprocity in bottlenose dolphins (Tursiops truncatus)

Abstract

Some moral behaviours, often regarded as reflecting high cognitive abilities (such as empathy, cooperation, targeted helping) are known to only be present in very few species, like great apes, elephants and cetaceans. Prosocial behaviours (producing a benefit for the recipient without necessarily involving a cost for the actor) have been mostly found in primates and, more recently, in elephants. Despite dolphins' reputation for helping their conspecifics, experimental studies about their prosocial and empathic abilities are rare. We conducted Prosocial Choice Tests in six bottlenose dolphins. The subjects had to choose between three objects: choosing the prosocial object induced the simultaneous rewarding of both the subject and a recipient individual; choosing the selfish object induced a reward only for the subject; choosing the null one did not reward anyone. We found prosociality and direct reciprocity in our subjects, and our results suggested that bottlenose dolphins might be able to modulate their prosocial and reciprocal tendencies according to partner-specific information. Subjects seemed to be more prosocial towards the other sex and more reciprocal towards same-sex recipients. This reciprocity might be underpinned by the same features that rule their behaviours in the wild (cooperating with same sex conspecifics). Moreover, an audience effect was reported, as the presence of the subject's young increased subjects' likelihood of prosocial response. Our findings highlighted that prosociality could appear in taxa other than primates, suggesting a convergent evolutionary phenomenon.

Keywords: Bottlenose dolphins; Prosociality; Reciprocity; Sex; Tursiops truncatus.