Abstract
In aggressive interactions, game theory predicts that animals should assess an opponent’s condition relative to their own prior to escalation or retreat. Despite the benefits of such mutual assessment, few studies have been able to reject simpler assessment strategies. Here we report evidence for mutual assessment in a wild primate. Gelada (Theropithecus gelada) males have conspicuous loud calls that may function as a signal of male quality. “Leader” males with harems putatively use loud calls to deter challenges from non-reproductive “bachelor” males. By contrast, leader males pose no threat to each other and congregate in large groups for a dilution effect against bachelors. In playback experiments and natural observations, gelada males responded to loud calls according to both their own and their opponent’s attributes. Although primates routinely classify others relative to themselves using individual attributes, this represents some of the first direct evidence for mutual assessment in primate signaling contests.
Highlights
In aggressive interactions, game theory predicts that animals should assess an opponent’s condition relative to their own prior to escalation or retreat
Do males attend differently to high- and low-quality calls based on their own status? We conducted a playback experiment on 60 adult geladas (20 females, 20 leader males, and 20 bachelor males) using previously recorded loud calls obtained during naturally-occurring displays between adult males (7 high-quality bouts and 7 low-quality bouts were used to construct 10 playback sets each containing a unique combination of one high- and one low-quality loud call bout from different males)
Gelada males, but not females, discriminated between loud calls based on the acoustic quality of the signal as well as their own status and quality
Summary
Game theory predicts that animals should assess an opponent’s condition relative to their own prior to escalation or retreat. In primate systems with linear dominance hierarchies, the dominance rank of an individual determines the outcome of most social interactions[25,26,27] These interactions are not thought to be based on the relative Resource Holding Potential (RHP) of contestants at the time of the interaction, but rather based on social knowledge of contestants derived from a recent history of interactions with them[28]. Results from previous research on mutual assessment have not been able to entirely distinguish whether primate subjects use individual identity or quality signals as the underlying basis for assessment, even in cases where playback experiments were able to manipulate the individual and/or the signal
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