Direct reciprocity in animals: The roles of bonding and affective processes

Abstract

The presence of direct reciprocity in animals is a debated topic, because, despite its evolutionary plausibility, it isbelieved to be uncommon. Some authors claim that stable reciprocal exchanges require sophisticated cognition whichhas acted as a constraint on its evolution across species. In contrast, a more recent trend of research has focused on thepossibility that direct reciprocity occurs within long-term bonds and relies on simple as well as more complex affectivemechanisms such as emotional book-keeping, rudimentary and higher forms of empathy, and inequity aversion, amongothers. First, we present evidence supporting the occurrence of long-term reciprocity in the context of existing bondsin social birds and mammals. Second, we discuss the evidence for affective responses which, modulated by bonding,may underlie altruistic behaviours in different species. We conclude that the mechanisms that may underlie reciprocalexchanges are diverse, and that some act in interaction with bonding processes. From simple associative learning in socialcontexts, through emotional contagion and behavioural mimicry, to empathy and a sense of fairness, widespread anddiverse social affective mechanisms may explain why direct reciprocity may not be a rare phenomenon among socialvertebrates.