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The convergent evolution of blue iris pigmentation in primates took distinct molecular paths

Authors

  • Wynn K. Meyer,

    Corresponding author
    • Department of Human Genetics, University of Chicago, Chicago, IL 60637
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    • These authors contributed equally to this work.

  • Sidi Zhang,

    1. Biological Sciences Collegiate Division, University of Chicago, Chicago, IL 60637
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    • These authors contributed equally to this work.

  • Sachiko Hayakawa,

    1. Department of Behavioral and Brain Sciences, Cognition and Learning Section, Primate Research Institute, Kyoto University, Inuyama, Japan
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  • Hiroo Imai,

    1. Department of Cellular and Molecular Biology, Molecular Biology Section, Primate Research Institute, Kyoto University, Inuyama, Japan
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  • Molly Przeworski

    1. Department of Human Genetics, University of Chicago, Chicago, IL 60637
    2. Department of Ecology and Evolutionary Biology, University of Chicago, Chicago, IL 60637
    3. Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637
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Correspondence to: Wynn K. Meyer, University of Chicago Department of Human Genetics, 920 E. 58th St., CLSC 416, Chicago, IL 60637, USA. E-mail: wynn@uchicago.edu

ABSTRACT

How many distinct molecular paths lead to the same phenotype? One approach to this question has been to examine the genetic basis of convergent traits, which likely evolved repeatedly under a shared selective pressure. We investigated the convergent phenotype of blue iris pigmentation, which has arisen independently in four primate lineages: humans, blue-eyed black lemurs, Japanese macaques, and spider monkeys. Characterizing the phenotype across these species, we found that the variation within the blue-eyed subsets of each species occupies strongly overlapping regions of CIE L*a*b* color space. Yet whereas Japanese macaques and humans display continuous variation, the phenotypes of blue-eyed black lemurs and their sister species (whose irises are brown) occupy more clustered subspaces. Variation in an enhancer of OCA2 is primarily responsible for the phenotypic difference between humans with blue and brown irises. In the orthologous region, we found no variant that distinguishes the two lemur species or associates with quantitative phenotypic variation in Japanese macaques. Given the high similarity between the blue iris phenotypes in these species and that in humans, this finding implies that evolution has used different molecular paths to reach the same end. Am J Phys Anthropol 151:398–407, 2013.© 2013 Wiley Periodicals, Inc.

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