The color vision typing using fecal DNA of New World monkeys and the analysis of vision-behavior relatedness

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Color vision polymorphism in New World monkeys results from allelic variation of the single-locus middle-to-long-wave-sensitive (M/LWS) opsin gene residing on the X-chromosome. This polymorphism is trans-specific, and thus generally believed to be maintained by some form of balancing selection. However, the presence of balancing selection has not been tested rigorously by population genetic parameters. At the level of a social group, which usually comprises no more than a few dozen individuals, presence or absence of color vision polymorphism is not well assessed. In addition, the advantage of trichromacy to primates is not entirely clear in the Neotropic environment, since many of the food resources that are available throughout the year appear cryptic to human observers.To investigate the mechanism behind the persistence of color vision polymorphism in New World monkeys, we examined free-ranging populations of white-faced capuchin monkeys (Cebus capucinus) and black-handed spider mon … More keys (Ateles geoffroyi) inhabiting Santa Rosa National Park, Costa Rica. We took a three-pronged approach : (1) assessment of color vision polymorphism in social groups by genotyping M/LWS opsin alleles using fecal DNA, (2) tests of the neutral hypothesis by evaluating nucleotide diversity of the M/LWS opsin gene, and (3) assessment of the behavioral significance of color vision variation by looking for correlations between color vision type and behavioral patterns such as foraging.We found that : (1) color vision polymorphism is indeed present in both capuchin and spider monkey groups, each comprising only 〜20 individuals, but with various allele compositions between groups and between species, (2) Tajima's D statistic is significantly positive for M/LWS opsin gene but it is not for the neutral controls, and (3) dichromatic capuchins are more efficient at insect foraging, and hue of fruits may not be a critical cue for trichromatic spider monkeys. These results indicate that the high level of color vision polymorphism can be explained only by some form of balancing selection, which would likely include factors other than heterozygote (= trichromat) advantage. Less