Go for Lipids! Food Preferences and Nutrient Composition in Zoo-Housed White-Faced Sakis, Pithecia pithecia

The role that single nutrients may play for food choices in nonhuman primates is not fully understood. White-faced sakis (Pithecia pithecia) are unusual among frugivorous primates as they do not serve as seed dispersers but rather exploit the seeds they consume, presumably for their high contents of lipids and proteins. Therefore, we assessed the occurrence of spontaneous food preferences in zoo-housed white-faced sakis and analyzed whether these preferences correlate with nutrient composition. Using a two-alternative choice test, we repeatedly presented three female and two male sakis with all possible binary combinations of 15 types of food that are part of their diet under human care, and found them to display the following rank order of preference: peanut > hazelnut > avocado > melon > egg > apple > mealworms > beetroot > carrot > cucumber > cabbage > tomato > sweet potato > broccoli > eggplant. This preference ranking significantly and positively correlated with the total energy content of the food items. However, we found the strongest positive correlation among the three macronutrients providing metabolic energy between the sakis' food preferences and lipid content. This is remarkable as all other primate species tested so far using this method displayed the strongest correlation with carbohydrates instead. Together with our finding that the sakis significantly preferred foods high in mono-unsaturated fatty acids, the building blocks of lipids, these results support the notion that white-faced sakis exploit the lipids contained in seeds to meet their requirements of metabolic energy.