Experimental evidence that EPA and DHA are dietary requirements in a migratory shorebird, but they do not affect muscle oxidative capacity.

Dietary n-3 long chain polyunsaturated fatty acids (LCPUFA) are hypothesized to be natural doping agents in migratory shorebirds, enabling prolonged flight by increasing membrane fluidity and oxidative capacity of the flight muscles. Animals can obtain n-3 LCPUFA from the diet or by conversion of dietary α-linolenic acid, 18:3 n-3. However, capacity to meet n-3 LCPUFA requirements from 18:3 n-3 varies among species. Direct tests of muscle oxidative enhancement and fatty acid conversion capacity are lacking in marine shorebirds that evolved eating diets rich in n-3 LCPUFA. We tested whether the presence and type of dietary fatty acids influence the fatty acid composition and flight muscle oxidative capacity in western sandpipers (Calidris mauri). Sandpipers were fed diets low in n-3 PUFA, high in 18:3 n-3, or high in n-3 LCPUFA. Dietary fatty acid composition was reflected in multiple tissues, and low intake of n-3 LCPUFA decreased abundance of these fatty acids in all tissues, even with a high intake of 18:3 n-3. This suggests that 18:3 n-3 cannot replace n-3 LCPUFA, and dietary n-3 LCPUFA are required for sandpipers. Flight muscle indicators of enzymatic oxidative capacity and regulators of lipid metabolism did not change. However, the n-3 LCPUFA diet was associated with increased FAT/CD36 mRNA expression, potentially benefitting fatty acid transport during flight. Our study suggests that flight muscle lipid oxidation is not strongly influenced by n-3 PUFA intake. The type of dietary n-3 PUFA strongly influences the abundance of n-3 LCPUFA in the body and could still impact whole-animal performance.