International Research Fellowship Program: Mechanisms Underlying Tactical Deception and Counterdeception in Capuchin Monkeys: Stress and Skepticism

Wheeler Brandon C, Jacksonville AR

Investigators

Abstract

The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twenty-four-month research fellowship by Dr. Brandon C. Wheeler to work with Dr. Julia Fischer at the German Primate Center in Gottingen, Germany with field work done at Iguazu National Park in Argentina. The cognitive abilities of primates are argued to have evolved so that individuals can outwit group-mates in competitive interactions by using, among other tactics, deceptive and counterdeceptive behaviors. However, because such behaviors are rare, the proximate mechanisms underlying these behaviors have not been examined in wild primates and it is thus unknown if they are indeed driven by cognitive mechanisms. Recent work by the PI with wild tufted capuchin monkeys in northeastern Argentina has shown that these primates use alarm calls (i.e., vocalizations normally given in response to predators) during feeding but when no predators are present. The calls often cause dominant individuals to run out of the food patch and allow the more subordinate caller to gain access to the food. However, listeners reduce the success of these deceptive alarms by ignoring them more often than they do honest alarms. As the first systematic evidence of deception and associated counter-deception in wild primates, this presents an ideal study system to examine if cognitive abilities are necessary to explain the observed behaviors. In the current study, the PI is investigating the mechanisms underpinning the observed deceptive and counter-deceptive behaviors in the same population of Argentine capuchin monkeys. Specifically, this study addresses two questions. First, because previous studies have indicated that alarm calling behaviors may be controlled by the production of cortisol, a hormone associated with stress, is it possible that deceptive alarms are driven proximately not by cognitive mechanisms, but by hormonal reactions to competition-induced stress? Second, is counterdeception better explained as a recognition of subtle acoustic differences between honest and deceptive alarm calls, or as skepticism of calls given in competitive contexts? The first question is addressed by experimentally manipulating food distribution and measuring the levels of cortisol excreted in the feces of dominant and subordinate individuals. The second question is addressed by analyzing audio recordings of honest and deceptive alarm calls to determine if they differ acoustically, and by playing audio recordings of deceptive alarm calls to the subjects in noncompetitive contexts to determine if they respond with antipredator reactions more often in the latter context than they do during competitive feeding contexts. Hormonal and bioacoustic analyses are being conducted at the German Primate Center in Göttingen, Germany. The results will elucidate the degree to which cognition underlies the deceptive and counterdeceptive behaviors observed in this species and may provide insight into the evolutionary origins these behaviors in humans. Beyond the project's intellectual merit, this grant funds training for a young US researcher in laboratory analyses which are increasingly being used to understand the evolution of behavior in primates and other animals. Such knowledge will prove critical as the PI moves forward in his teaching and research career, as will the collaborative relationships developed between the PI and international research institutions during the funding period.