Chabaud, C. | bioRxiv Science

bioRxiv2025

Oxidation and allocation of nectar amino acids during butterfly flight

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.

physiology↗

bioRxiv2025

Shifts in nutrient allocation in a gift-giving butterfly: A hidden consequence of water balance?

As climate change intensifies drought, understanding how animals maintain fitness under water stress is key to predicting species persistence. Animals use diverse behavioural and physiological adjustments to avoid dehydration. However, the physiological and fitness costs of these mechanisms are often overlooked, despite their potential to shift nutrient acquisition and allocation. We hypothesized that maintaining water balance, through increased water intake and/or decreased water loss, leads to nutrient shifts and trade-offs in Pieris rapae butterflies. In this species, females receive a protein- and water-rich nuptial gift (NG), known to enhance fecundity and possibly mitigate dehydration. We quantified the impact of dry conditions on female hydration and fitness, using stable isotopes to trace nutrient allocation to storage, fecundity, and catabolism. We found that the NG, combined with reduced respiratory water loss, contributed to maintaining female water balance in dry conditions. Importantly, while dry environments did not impact potential fecundity, nutritional shifts and trade-offs that could affect long-term fitness were evident: females allocated more lipids to eggs at the expense of long-term storage, while reducing catabolism of NG-derived leucine. This interplay among water balance, nutrient allocation, and fitness emphasizes the importance of linking water balance mechanisms with broader nutrient-use strategies under environmental stress.

ecology↗