You lick me, I like you: understanding the function of allogrooming in ungulates

Allogrooming is a common affiliative behaviour with hygienic, physiological and social consequences, and has historically been examined in non-human primates in order to understand the evolution of sociality. In primates, allogrooming is well-known to have evolved for an antiparasitic function, leading to physiological consequences and further adoption of the behaviour for social functions. This includes exchanging benefits in a biological market, post-conflict reconciliation and long-term social bond formation. The relevant importance of these functions is largely undetermined in many non-primate taxa, including ungulates. We aimed to evaluate the current evidence for allogrooming function in ungulates, asking whether the behaviour serves a social function, and if so, to what magnitude. Ungulates show large differences in their allogrooming behaviour, but the variation of these has not been truly understood. We find that although allogrooming in ungulates has been co-opted for social purposes such as bond formation, the variety of these has not been fully explored. Identifying species-specific allogrooming functions can help to clarify the context of behaviour; this allows us to improve our knowledge of how individuals and groups interact within a population, and understand the implications of this behaviour when deducing animal state and sociality. We conclude that there is great potential for additional research into the benefits of affiliative behaviour in ungulates, and we encourage further exploration into the social functions of allogrooming in ungulates. Allogrooming has hygienic, physiological, and social consequences, including exchanging benefits in a biological market, post-conflict reconciliation, and long-term social bond formation. The relevant importance of these functions is largely undetermined in many non-primate taxa, including ungulates. We evaluated the current evidence of allogrooming function in ungulates. We find that allogrooming in ungulates has been co-opted for social purposes, but the variety of these has not been fully explored, and there is great potential for additional research into the benefits of affiliative behaviour in ungulates.image