The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Using a howler monkey hybrid zone (Alouatta pigra x Alouatta palliata) to understand social variation


1Department of Psychology, University of Michigan, 2Department of Ecology and Evolutionary Biology, University of Michigan

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Natural hybridization occurs in several primate taxa, but primate hybrid zones remain relatively understudied, despite having the potential to offer insight into both causes and consequences of phenotypic variation. To analyze the causes of variation in social behavior, I examined proximity in two species of howlers and their hybrids: Alouatta pigra, Alouatta palliata, and A. pigra x A. palliata (respectively located in the Mexican states of Campeche, Veracruz, and Tabasco). Work in pure populations has shown that A. pigra maintain higher proximity than A. palliata, but we do not know how genetics, ecology, and other social factors (e.g. the smaller groups of A. pigra) contribute to this difference. Here, I compared spacing patterns across species ancestry, location (a proxy for environmental disturbance), group size, and sex in 17 groups of howlers (A. pigra = 3, A. palliata = 3, A. pigra x A. palliata = 11) using 10,175 scan samples recorded in 2011 and 2012. On average, A. pigra female-female and female-male dyads were significantly closer together than the same dyad types in A. palliata or hybrids. Interestingly, hybrid proximity overall resembled A. palliata, even though the sample contains an even mix of pigra-like and palliata-like hybrids, and the hybrid zone is more highly disturbed than the two purebred sites. Further analysis revealed that group size explains some of the similarity (smaller groups are closer); however, after controlling for group size, ancestry continued to have an effect. These results are consistent with a genetic basis for certain behavioral differences.

This study was funded by the University of Michigan and the National Science Foundation.

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