The Behavioral Ecology of Color Vision: Considering Fruit Conspicuity, Detection Distance and Dietary Importance

Primate color vision is well suited for investigating the genetic basis of foraging behavior owing to a clear genotype-phenotype linkage. Finding fruits amid tropical foliage has long been proffered as an adaptive explanation for primate trichromacy, yet there is a dearth of systematic evaluations of frugivory as an ecological selective force. We studied the behavioral ecology of wild capuchins (Cebus capucinus) in northwestern Costa Rica across the annual cycle and modeled the ability of three dichromatic and three trichromatic phenotypes to discriminate fruits from leaves, a task that represents long-distance search for food patches in a tropical forest. Models of the trichromatic phenotypes could correctly discriminate approximately three-quarters of the total capuchin dietary fruits from leaves, including some fruits subjectively classified as having "cryptic" (greenish-brownish) hues. In contrast, models of dichromatic phenotypes could discriminate fewer than one-third of the fruits. This pattern held when we restricted our analysis to only the most heavily consumed diet items, preferred foods, or seasonally critical species. We in addition highlight the potential of fruit species with small patch sizes to confer an advantage to trichromats, as these resources are anticipated to provide a high finder's reward. Our results are consistent with the hypothesis that long-distance detection of fruit patches exerts a selective pressure on trichromacy in neotropical primates, and suggest that greenish-brownish fruits might have played an underappreciated role in the evolution of primate color vision.