GUGLIELMO, CG*; PRICE, ER; HAYS, QR; Univ. of Montana; Univ. of Montana; Univ. of Montana: The effects of diet macronutrient composition on fuel selection during exercise in a migratory bird Dendroica coronata

In mammals diet macronutrient composition affects exercise fuel utilization and endurance performance. High carbohydrate diets used by marathon athletes enhance glycogen utilization, high fat diets increase the efficiency of fatty acid utilization, and protein intake may affect the rate of protein oxidation. Many birds switch from a high protein diet of invertebrates to fruits or seeds (high carbohydrate or fat) during migration, and a previous interspecific study of migratory passerines suggested that in-flight fuel mixture is related to diet. In this study we examine a single species that naturally diet switches during migration and ask how may an individual�s diet choice affect its pattern of fuel utilization? We acclimated Yellow-rumped warblers to semi-synthetic fruit (high carbohydrate, low protein) or insect (low carbohydrate, high protein) diets and exercised them in a flight-wheel respirometer. Respiratory exchange ratios were similar among diet treatments at rest and during exercise, but diet had a major impact on fuel selection as indicated by plasma metabolite profiles. Following 45 min of strenuous exercise plasma concentrations of glycerol and B-OH-butyrate did not differ between diet treatments. However, fruit birds had higher non-esterified fatty acid and triglyceride levels. Fruit birds became substantially hypoglycemic and tended also to have lower uric acid levels. This indicates that the low protein, fruit diet enhanced fat utilization and spared protein, but may have impaired gluconeogenic pathways. Therefore, a physiological tradeoff between diet selection and exercise fuel utilization may exist at the individual level, which may influence the evolution of migratory patterns.