Evidence for mutual assessment in a wild primate

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.

Vocal and movement responses of mantled howler monkeys (Alouatta palliata) to natural loud calls from neighbors

“…Finally, groups usually moved away from calling neighbors that were closer, a result that opposes the third prediction. Overall, our results converge with previous evidence that the responses of howler monkeys (reviewed in Kitchen et al, 2015) and other primates (e.g., Benítez et al, 2017;Ouattara et al, 2009;Wich et al, 2001) to conspecific loud calls are complex (Cheney & Seyfarth, 2003), and are associated with the integration of contextual information (Seyfarth & Cheney, 2017).…”

Chest beats as an honest signal of body size in male mountain gorillas (Gorilla beringei beringei)

“…Gorilla chest beats are thought to play a key role in male–male competition allowing individuals to assess the fighting ability of competitors and thus influence whether they should initiate, escalate or retreat in intra- and intergroup contests 22 , 31 , 42 . Similarly, male gelada baboons ( Theropithecus gelada ) assess the competitive ability of rivals through vocalizations and compare it to their own, governing how they respond in contests 43 . Intense contact aggression between males is infrequent in gorillas, which is presumed to reflect the high costs of aggression and their ability to resolve conflicts without resorting to this high risk behaviour (within-group 31 , 42 ; between-group 44 ).…”

Using ternary plots to investigate continuous variation in animal contest strategies

“…In conclusion, if used in conjunction with existing approaches for the study of agonistic interactions, ternary plots can provide a way of achieving a greater level of granularity from contest data, particularly when MA is evident, by illustrating the relative contributions of information on self and opponent RHP, as well as that of RV. Although several studies have presented evidence for mutual assessment (Benítez, Pappano, Beehner, & Bergman, 2017;Tedore & Johnsen, 2015;Tibbetts, Mettler, & Levy, 2010), it is difficult to gauge the balance between the contributions of information on self and opponent RHP to the giving up decision. However, this information is likely to be present already in data sets that contain contest duration and the RHP of both opponents, and these data could be used to populate ternary plots.…”