Abstract:
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 camou aged 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 tri-
chromats. We classi ed 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 pro les, but we found evidence of niche differen-
tiation in the invertebrate prey consumed. In support for our prediction regarding cryptic invertebrate
prey, dichromats ate more camou aged surface-dwelling invertebrates, while trichromats ate more
extracted ants. Contrary to our prediction regarding reddish foods, dichromats consumed more dark
reddish gs 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 exibility driven by
sensory differences may decrease intragroup feeding competition while meeting species-speci c
nutritional needs. Our research sheds light on the extent of foraging niche differentiation in a popula-
tion of wild mammals and its potential contribution to maintaining colour vision polymorphism.
