Maillet Dominique, Weber Jean-Michel
Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, K1N 6N5, Canada.
J Exp Biol. 2006 Jul;209(Pt 14):2686-95. doi: 10.1242/jeb.02299.
At the end of summer, semipalmated sandpipers (Calidris pusilla) traveling from the Arctic stop in the Bay of Fundy (east coast of Canada) to build large fat reserves before a non-stop flight to South America. During a 2-week stopover, the body mass of this small shorebird is doubled ( approximately 20 g to 40 g) by feeding on a burrowing amphipod, Corophium volutator, that contains unusually high levels of n-3 polyunsaturated fatty acids (PUFA). In mammals, high n-3 PUFA content of membrane phospholipids (PL) is linked to improved exercise performance due to increased membrane fluidity that accelerates transmembrane lipid transport. We hypothesized that dietary n-3 PUFA could be used as a natural ;performance-enhancing substance' by semipalmated sandpipers to prepare their flight muscles for migration. Also, PUFA stored as fuel in neutral lipids (NL) can be mobilized more quickly than saturated fatty acids, but they contain less energy per unit mass. It is therefore unclear whether dietary fatty acids are modified before storage. Birds were collected at various stages of fat loading to examine changes in the composition of tissue PL (membranes) and NL (fuel stores). Results show that dietary n-3 PUFA are incorporated in tissue lipids in less than 2 weeks. During the stopover, the double bond index of muscle PL increases by 25% and the fatty acid profiles of both muscle PL and adipose NL converge with that of the diet. However, >50% of dietary n-3 PUFA are converted to other fatty acids before storage, mainly to oleate (18:1), possibly because monounsaturates offer a compromise between high energy density and ease of mobilization. This study shows that long-distance migrant birds can (1) use natural diets rich in specific lipids to prime flight muscles for endurance exercise, and (2) modify dietary fatty acids before storing them as fuel.
夏末时分，从北极地区迁徙而来的半蹼滨鹬（Calidris pusilla）会在芬迪湾（加拿大东海岸）停留，在不停歇地飞往南美洲之前积累大量脂肪储备。在为期两周的中途停留期间，这种小型滨鸟通过捕食一种穴居的双壳类动物——卷钩虾（Corophium volutator），体重翻倍（从约20克增至40克），而这种虾含有异常高含量的n-3多不饱和脂肪酸（PUFA）。在哺乳动物中，膜磷脂（PL）中高含量的n-3 PUFA与运动表现的改善有关，这是因为膜流动性增加加速了跨膜脂质转运。我们推测，半蹼滨鹬可将饮食中的n-3 PUFA用作一种天然的“性能增强物质”，为其飞行肌肉的迁徙做好准备。此外，作为燃料储存在中性脂质（NL）中的PUFA比饱和脂肪酸能更快地被调动，但每单位质量所含能量较少。因此，尚不清楚饮食中的脂肪酸在储存前是否会发生改变。在脂肪积累的不同阶段收集鸟类样本，以研究组织PL（膜）和NL（燃料储备）成分的变化。结果表明，饮食中的n-3 PUFA在不到两周的时间内就被整合到组织脂质中。在中途停留期间，肌肉PL的双键指数增加了25%，肌肉PL和脂肪NL的脂肪酸谱都与饮食中的脂肪酸谱趋同。然而，超过50%的饮食n-3 PUFA在储存前会转化为其他脂肪酸，主要转化为油酸（18:1），这可能是因为单不饱和脂肪酸在高能量密度和易于调动之间达到了一种平衡。这项研究表明，长途迁徙鸟类能够：（1）利用富含特定脂质的天然饮食为耐力运动的飞行肌肉做好准备；（2）在将饮食中的脂肪酸储存为燃料之前对其进行改造。
