Fruit Choice by Two Sympatric Primate Species: Determining Nutritional Composition Using Visual and Tactile Cues

In forested environments it is challenging for fruit-eating animals to select fruits that meet their nutritional needs. Primates base their food choices on fruit phenotypic traits such as color and tactile cues to determine nutrient content to improve foraging efficiency. However, are fruit phenotypic traits reliable indicators of nutrient content? To answer this question, we integrated observations of feeding behavior with the nutritional and physical characteristics of the fruits in the diet of two sympatric primates (Nomascus concolor and Trachypithecus crepusculus) in a subtropical forest in Southwestern China. Gibbons chose fruits with high total non-structural carbohydrate content that have high chromatic contrast against a predominantly green background, while langurs chose fruits with high crude protein content and high hardness. The chromatic contrast exhibited a significant positive correlation with the carbohydrate content, and the fruit hardness demonstrated a significant positive correlation with the protein content. Chromatic conspicuousness and hardness may serve as important fruit foraging cues for gibbons and langurs. This study adds to our growing understanding of how Old World primates use color vision and tactile cues while foraging and provides new insights to the evolution of diverse animal sensory systems.