Cheating individuals alter their behavior to avoid detection, known as tactical deception, which allows them to avoid the social costs of their actions. Evidence for tactical deception is surprisingly difficult to document in wild primates. Thore J. Bergman (University of Michigan, Ann Arbor) and researchers at University of the Free State Qwaqwa (Phuthadijhaba, South Africa) studied the mating behavior of wild geladas (Theropithecus gelada). In these primate societies, the dominant male sires the majority of offspring, but a few subordinate males also sire a small percentage of the unit's offspring. These 'extra-pair copulations' elicit aggression from the male, creating an incentive for the guilty parties to conceal their mating. Because the geladas live in an open grassland habitat and typically vocalize loudly during mating, the researchers theorized that such concealment would be difficult unless the individuals modified their usual mating behavior.
They observed that individuals involved in extra-pair copulations exhibited deceptive behaviors: they were less likely to vocalize during copulation and more likely to copulate a safe distance of 20 m or more away from the dominant male (Nat. Commun. doi:10.1038/ncomms2468; published online 12 February 2013). The authors suggest that this species may provide a potential model of deception in natural settings.
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