Oxidation and allocation of nectar amino acids during butterfly flight

Abstract

Flying animals face extreme energetic demands, relying mainly on carbohydrates and lipids, with occasional contributions from proteins and amino acids. In nectar-feeding species like butterflies and hummingbirds, sugars are the primary fuel, yet the extent to which other nectar-derived nutrients, like amino acids, are used for flight or retained for other functions remains unclear. Using 13C-labeled nectar, we tracked the metabolic fate of sugars and amino acids during flight in Pieris rapae butterflies. We found that proline and glycine, two of the most abundant nectar amino acids, were oxidized alongside sugars. Importantly, flight intensity modulated nutrient allocation from nectar: high-flight females incorporated less glycine into tissues, implying diversion toward flight, while threonine deposition in abdomens increased, reflecting prioritization for reproduction and storage. These findings reveal the complex role of nectar-derived nutrients in supporting locomotion and reproduction, while showing how nectar use can modulate trade-offs between flight and fecundity.