Does colour vision type drive dietary and nutritional niche differentiation in wild capuchins (Cebus imitator)?

The polymorphic colour vision system of platyrrhine monkeys is a remarkable example of balancing selection. Yet, the underlying mechanism of natural selection remains debated. Here we test the potential for dietary niche differentiation between sensory phenotypes. Monkeys with dichromacy (red-green ‘colourblindness’) are predicted to eat more camouflaged foods while trichromatic monkeys (‘typical’ human-like colour vision) are predicted to eat more reddish foods. We studied a population of wild Costa Rican capuchins (Cebus imitator), comparing the diet and nutrition of adult female dichromats and trichromats. We classified the conspicuity of diet items in capuchin visual space and calculated dietary intake, nutritional intake and niche overlap during periods of high and low habitat-wide fruit abundance. Dichromats and trichromats had similar nutritional profiles, but we found evidence of niche differentiation in the invertebrate prey consumed. In support for our prediction regarding cryptic invertebrate prey, dichromats ate more camouflaged surface-dwelling invertebrates, while trichromats ate more extracted ants. Contrary to our prediction regarding reddish foods, dichromats consumed more dark reddish figs than did trichromats. However, these fruits were likely to be conspicuous to both dichromats and trichromats in luminance contrast. Overall, our results suggest that monkeys with different colour vision types achieve similar nutritional intakes in slightly different ways. Behavioural flexibility driven by sensory differences may decrease intragroup feeding competition while meeting species-specific nutritional needs. Our research sheds light on the extent of foraging niche differentiation in a population of wild mammals and its potential contribution to maintaining colour vision polymorphism. •Dichromatic and trichromatic capuchins exhibited modest dietary differences.•Dichromatic and trichromatic capuchins did not differ in nutritional niches.•Food and nutrient intake by capuchins were shaped by fruit abundance.•Dietary niche differentiation may help maintain polymorphic colour vision.