Eikenaar Cas, Winslott Erica, Schmaljohann Heiko, Wang Hong-Lei, Isaksson Caroline
Institute of Avian Research, Wilhelmshaven, 26386, Germany.
Department of Biology, Lund University, Lund, SE-223 62, Sweden.
Physiol Behav. 2022 May 15;249:113768. doi: 10.1016/j.physbeh.2022.113768. Epub 2022 Mar 2.
During migratory endurance flights, which are energetically very demanding, migrants have to deal with prolonged elevated generation of reactive oxygen species (ROS). To limit the damaging actions that ROS have on lipids and proteins, migrating birds are known to upregulate their antioxidant defence system. However, there may be additional ways to limit oxidative damage incurred from flying. Migratory endurance flights are fuelled mainly with fatty acids (FAs), and the risk of their peroxidation (resulting in oxidative lipid damage) increases with the number of double bonds in a FA, with polyunsaturated FAs (2 or more double bonds, PUFAs) being most peroxidation-prone. By fuelling their flights with relatively few PUFAs, migratory birds could thus limit oxidative lipid damage. Within migratory birds, there is considerable variation in the length of their flights, with nocturnal migrants making lengthier flight bouts, thus more likely to experience lengthier periods of elevated ROS production, than diurnal migrants. However, whether migrants making lengthier flights incur more oxidative lipid damage is unknown. Neither is it known whether flight length and FA composition are associated. Therefore, we determined plasmatic malondialdehyde level, a marker of oxidative lipid damage, and FA composition of three nocturnal and two diurnal migrant species caught at an autumn stopover site. We found little inter-specific variation in malondialdehyde level, indicating that the amount of oxidative lipid damage was comparable across the species. In contrast, the species strongly differed in their plasmatic FA composition. The nocturnal migrants had significantly lower relative PUFA levels than both diurnal migrants, an effect mainly attributable to linoleic acid, an essential (strictly dietary) FA. Consequently, the susceptibility of plasmatic FAs to lipid peroxidation was significantly lower in the nocturnal than diurnal migrants. Because in birds, energy expenditure during flight decreases with the degree of FA unsaturation, we interpret our observation of lower PUFA levels in nocturnal migrants as support for the idea that utilizing PUFA-poor fuel can help migrating birds to curb oxidative lipid damage.
在能量需求极大的迁徙耐力飞行过程中，候鸟必须应对活性氧（ROS）长时间的高水平产生。为了限制ROS对脂质和蛋白质的破坏作用，已知迁徙鸟类会上调其抗氧化防御系统。然而，可能还有其他方法来限制飞行过程中产生的氧化损伤。迁徙耐力飞行主要以脂肪酸（FAs）为燃料，脂肪酸过氧化（导致脂质氧化损伤）的风险会随着脂肪酸双键数量的增加而上升，其中多不饱和脂肪酸（含2个或更多双键，PUFAs）最容易发生过氧化。因此，通过以相对较少的PUFAs为飞行提供燃料，候鸟可以限制脂质氧化损伤。在候鸟中，它们飞行的时长存在很大差异，夜间迁徙的鸟类飞行时段更长，因此比白天迁徙的鸟类更有可能经历更长时间的ROS高水平产生期。然而，飞行时间更长的候鸟是否会遭受更多的脂质氧化损伤尚不清楚。飞行时长与脂肪酸组成是否相关也不为人知。因此，我们测定了在一个秋季中途停歇地捕获的三种夜间迁徙鸟类和两种白天迁徙鸟类的血浆丙二醛水平（脂质氧化损伤的一个标志物）以及脂肪酸组成。我们发现丙二醛水平在种间差异不大，这表明脂质氧化损伤的程度在不同物种间具有可比性。相比之下，这些物种的血浆脂肪酸组成差异很大。夜间迁徙鸟类的相对PUFA水平显著低于白天迁徙鸟类，这种差异主要归因于亚油酸，一种必需（严格依赖饮食摄入）脂肪酸。因此，夜间迁徙鸟类血浆脂肪酸发生脂质过氧化的敏感性显著低于白天迁徙鸟类。由于在鸟类中，飞行过程中的能量消耗会随着脂肪酸不饱和度的增加而降低，我们将在夜间迁徙鸟类中观察到的较低PUFA水平解释为支持以下观点的证据：利用富含较少PUFA的燃料有助于候鸟抑制脂质氧化损伤。
