The polymorphic color vision system present in most North, Central, and South American monkeys is a textbook case of balancing selection, yet the mechanism behind it remains 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 data set of behavioral scan samples (n = 21 984) from 48 wild adult female capuchins of known color vision genotype, dominance rank, and reproductive status, together with models of food conspicuity. We find no significant differences between dichromats and trichromats in the frequency of scans spent foraging for different food types but do find that nursing females forage less overall than cycling females. Our results suggest that the potential for color-vision-based niche differentiation in foraging time may be curtailed by the energetic requirements of reproduction, behavioral synchrony caused by group living, and/or individual preferences. While niche differentiation in activity budgets by color vision type is not apparent, fine-scale niche differentiation may be occurring. This research enhances our understanding of the evolutionary processes maintaining sensory polymorphisms.

中文翻译：

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用多态色觉测试野生卷尾猴的生态位分化假设

大多数北美、中美和南美猴子的多态色觉系统是平衡选择的教科书案例，但其背后的机制仍然知之甚少。以前的工作已经确定了针对不同色觉表型的特定任务觅食优势：二色视觉动物（红绿色盲）对无脊椎动物的觅食效率更高，而三色视觉动物（相对于人类的颜色“正常”）对于“带红色”成熟果实的觅食效率更高，表明生态位分化可能是维持色觉变化的基础。我们通过询问二色和三色卷尾猴（Cebus 模仿者）的觅食活动预算是否存在差异来探索生态位分化假设的预测，专门测试重色视是否更频繁地觅食无脊椎动物，而三色视是否更频繁地觅食“带红色”的成熟果实。为了评估这一点，我们分析了来自 48 只已知色觉基因型、优势等级和生殖状态的野生成年雌性卷尾猴的行为扫描样本 (n = 21 984) 的大型数据集，以及食物显眼模型。我们发现二色视觉者和三色视觉者在寻找不同食物类型的扫描频率方面没有显着差异，但确实发现哺乳期女性的总体觅食量低于骑自行车的女性。我们的研究结果表明，觅食时间中基于颜色视觉的生态位分化的潜力可能会受到繁殖的能量需求、群体生活引起的行为同步和/或个人偏好的限制。虽然按色觉类型划分的活动预算的利基差异并不明显，但可能会出现精细的利基差异。这项研究增强了我们对维持感觉多态性的进化过程的理解。