Between-group variation in production of pant-grunt vocalizations by wild bonobos (Pan paniscus)

The potential for aggression is inherent in social interaction, and strategies to reduce the costs of aggression are ubiquitous among group-living animals. One strategy employed by lower-ranking individuals in a variety of species is the production of subordination signals, which are formal signals that communicate the signaler's inferior status relative to the recipient of the signal. Here, we report the results of our investigations into (1) the presence and usage of the pant-grunt vocalization in two populations of wild bonobos; (2) the relationship between the production of pant-grunts and agonistic predictability across the genus Pan. We find stark differences in production of pant-grunts in the two populations: bonobos at the LuiKotale field site regularly used pant-grunts as a signal of subordination (primarily, though not exclusively, among male-male dyads); in contrast, at the Kokolopori field site, adult bonobos were never observed producing pant-grunts. Across Pan, we find weak support for an association between agonistic predictability and production of pant-grunt vocalizations.Significance statementThere have been conflicting reports on whether bonobos, like chimpanzees, produce the submissive pant-grunt vocalization. We confirm the presence of the pant-grunt in the bonobo vocal repertoire, and document variation in its production across communities. We also suggest that variation in pant-grunt production across the genus Pan may be explained by the predictability of dominance interactions.