Collaborative Research: Causes and Consequences of Vocal Variation in a Howler Monkey (Alouatta spp.) Hybrid Zone: An Integrated Behavioral, Morphological and Genetic Approach

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Hybrid zones typically encompass a variety of taxonomically and genetically distinct individuals living under similar ecological and social conditions. Thus, hybrid zones represent unique opportunities to separate intrinsic and extrinsic causes of variation among animals. Furthermore, because a variety of animals are in direct competition, hybrid zones are also ideal locations for studies of competitive ability. This project focuses on two species of howler monkeys, Alouatta palliata and A. pigra, with different vocalizationsthat hybridize in a small region in southern Mexico. The research builds on previous morphological and genetic sampling of the hybrid zone and addresses two main questions: 1) what causes vocal variation among A. palliata, A. pigra, and hybrids? and, 2) how do different vocalizations impact competitive ability in the hybrid zone? To address these questions the project integrates molecular, morphological, behavioral, and acoustic data with playback experiments. Sources of vocal differences will be uncovered by comparing vocalizations among purebred and hybrid males to their genetic background, morphology, location, and social setting. The playback experiments involve both males and females and reveals the types of calls that males find intimidating or females find attractive (or both). The study examines the proximate and ultimate factors shaping primate vocalizations, how sexual selection structures admixture and gene flow, and how differences in vocalizations affect sexual selection. The project is highly collaborative and will strengthen research ties at many levels; between departments at the University of Michigan, between the University of Michigan and Ohio State University, and internationally between US universities and the Universidad Veracruzana in Mexico. In addition to providing considerable training to Mexican and US students, the project will directly benefit conservation through an educational workshop directed to school-age children within the area of hybridization. Furthermore, the presence of a long-term study in the region and the inclusion of Mexican researchers and students will promote primate studies and conservation in Mexico, a country of high biogeographic importance for primates and other Neotropical taxa.