Testing the niche differentiation hypothesis in wild capuchin monkeys with polymorphic color vision

The polymorphic color vision system of most North, Central, and South American monkeys is a textbook case of balancing selection, yet the mechanism behind it is poorly understood. Previous work has established task-specific foraging advantages to different color vision phenotypes: dichromats (red-green colorblind) are more efficient foraging for invertebrates, while trichromats (color “normal” relative to humans) are more efficient foraging for “reddish” ripe fruit, suggesting that niche differentiation may underlie the maintenance of color vision variation. We explore a prediction of the niche differentiation hypothesis by asking whether dichromatic and trichromatic capuchin monkeys (Cebus imitator) diverge in their foraging activity budget, specifically testing whether dichromats forage more frequently for invertebrates and trichromats forage more frequently for “reddish” ripe fruit. To assess this, we analyze a large dataset of behavioral scan samples (n = 21,984) from 48 wild adult ...