3 research outputs found

    The structural and motivational role of the unique lipā€flip movement in the gelada (Theropithecus gelada) facial display repertoire

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    ObjectivesHuman language represents an extreme form of communicative complexity. Primate facial display complexity, which depends upon facial mobility, can be used as a model for the study of the evolution of communicative complexity. The gelada (Theropithecus gelada) is the only primate that can produce a lipā€flip eversion. This study investigates the role of the lipā€flip relative to the baredā€teeth display to understand its role in generating communicative complexity.Materials and methodsWe reviewed videos of gelada social interactions. We utilized the facial action coding system (FACS) to define structural component action units (AUs) of each display. We inferred display motivation from the behaviors of the display sender.ResultsThe lipā€flip was used only in combination with the essential AUs of the baredā€teeth display, serving as an optional structural element added to produce a structural variant. Both the baredā€teeth display with and without a lipā€flip occurred most frequently with nonaggressive, submissive behaviors. The lipā€flip was more frequently preceded by approach than the baredā€teeth display, especially in males. The lipā€flip was also present in the majority of structurally blended facial displays though the motivation of the nonā€lipā€flip parent display often dominated.DiscussionThe lipā€flip may potentially function as an indicator of benign intent after an approach or as an intensifying component of nonaggressive intent. Adaptations to increase facial mobility in geladas via facilitating the lipā€flip may promote increased communicative complexity through increased conspicuousness and motivational signaling specification or intensification.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155514/1/ajpa24031_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155514/2/ajpa24031.pd
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