Social inhibitory control in five lemur species
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We tested five lemur species—ring-tailed lemurs, ruffed lemurs, mongoose lemurs, black lemurs, and Coquerel’s sifakas—(N = 52) in an experiment that evaluated skills for inhibitory control in a social context. First, two human experimenters presented identical food rewards; the “generous” experimenter allowed the subject to eat from her hand, whereas the “competitive” experimenter always withheld the reward. Lemurs quickly learned to approach the generous experimenter and avoid the competitive one. In the inhibition test phase, we endowed the competitive experimenter with a more valuable food reward but the competitive experimenter continued to withhold food from the subject. Thus, lemurs were required to inhibit approaching the more desirable reward in favor of the lesser but obtainable reward presented by the generous experimenter. In test trials, lemurs’ tendency to approach the competitive experimenter increased from the reputation phase, demonstrating sensitivity to the experimental manipulation. However, subjects approached the larger reward less frequently in test trials compared with pretest food-preference trials, evidencing some capacity for inhibitory control in this context. Despite differences in sociality and ecology, the five lemur species did not differ in this ability. Although the study did not uncover species differences, this experimental task may provide a useful measure of social inhibition in broader comparative studies.
KeywordsStrepsirrhines Cognitive evolution Inhibition Lemur cognition
We thank the staff at the Duke Lemur Center, especially Dr. Sarah Zehr and David Brewer, without whom this project would not have been possible. We also thank Camila Caceres, Jesse St. Clair, Alex Lourie, and Isabel Bernstein for their help with data collection, and Laura Lewis for her help with coding. We thank Jeff Stevens and three anonymous reviewers for their helpful feedback on earlier versions of this manuscript. This research was supported by the National Science Foundation (Grant BCS-10-25172), the Howard Hughes Research Fellows program, and the Duke Undergraduate Research Support Office.
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