Doctoral Dissertation Improvement: Are gelada loud calls "sexually-selected signals"?

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Geladas (Theropithecus gelada), like humans, live in unusually large social groups with numbers that exceed 1000 individuals. Unlike humans, however, the dominant males in gelada society do not recognize other males around them - even males that they encounter on a daily basis. This creates a socially and evolutionarily (fitness-related) significant set of limitations for males competing for mates; mainly, how to assess rivals prior to engaging in costly forms of competition. Species that do not use individual recognition for assessment typically use short-hand proxies; i.e., particular physical features or other characteristics ("signals") which are useful for ascertaining the competitive abilities of potential rivals. Although such signals in primates are rare, the unusually large groups found in gelada society may have favored their evolution through a form of natural selection referred to as "sexual selection."Research by doctoral student Marcela Benitez (University of Michigan), under the supervision of Dr. Jacinta Beehner, will examine one such putative signal for male geladas living in the Simien Mountains National Park, Ethiopia - a loud vocalization used in male displays (i.e., "loud calls"). Establishing whether loud calls are evolved signals requires establishing the following: (1) that variation exists in loud calls across males of different quality, (2) that males can use these calls to distinguish between high and low quality males, (3) that males then base challenges on these calls, and (4) that males with high quality calls have higher fitness (reproductive success). To address these predictions, this interdisciplinary research will combine acoustic, experimental, hormonal, and observational analyses on known individuals that have been followed continuously for the past six years. As such, the research represents one of the most comprehensive studies of what are theoretically termed "sexually-selected signals" (i.e., those evolved through male-male reproductive competition) with potential fitness consequences in a primate.This research is part of a long-term project that is committed to increasing conservation awareness and scientific education, both in the U.S. and in Ethiopia, through collaborative research and educational presentations to local people and eco-tourists in Ethiopia. The doctoral student Co-PI, a member of an underrepresented group in science, will incorporate the research into her bilingual website for childhood educational outreach, promoting engagement with the sciences by US children.