Data from: Low intensity blood parasite infections do not reduce the aerobic performance of migratory birds

Blood parasites (Haemosporidia) are thought to impair the flight performance of infected animals, and therefore, infected birds are expected to differ from their non-infected counterparts in migratory capacity. Since haemosporidians invade host erythrocytes, it is commonly assumed that infected individuals will have compromised aerobic capacity, but this has not been examined in free-living birds. We tested if haemosporidian infections affect aerobic performance by examining metabolic rates and exercise endurance in migratory great reed warblers (Acrocephalus arundinaceus) experimentally treated with Plasmodium relictum pGRW04 and in naturally infected wild birds over consecutive life history stages. We found no effect of acute or chronic infections on resting metabolic rate, maximum metabolic rate or exercise endurance in either experimentally treated or free-living birds. Oxygen consumption rates during rest and while undergoing maximum exercise as well as exercise endurance increased from breeding to migration stages in both infected and non-infected birds. Importantly, phenotypic changes associated with preparation for migration were similarly unaffected by parasitaemia. Consequently, migratory birds experiencing parasitaemia levels typical of chronic infection do not differ in migratory capacity from their uninfected counterparts. Thus, if infected hosts differ from uninfected conspecifics in migration phenology, another mechanism than changes in aerobic capacity should be involved.

血孢子虫（Haemosporidia）被认为会损害感染宿主的飞行能力，因此感染该寄生虫的鸟类在迁徙能力上应与未感染个体存在差异。由于血孢子虫会侵入宿主红细胞（erythrocytes），学界通常推测感染个体的有氧代谢能力会受损，但这一假说尚未在野生自由活动的鸟类中得到验证。本研究以迁徙性鸟类大苇莺（Acrocephalus arundinaceus）为研究对象，通过检测经实验感染残疟原虫（Plasmodium relictum）pGRW04株的个体，以及自然感染的野生个体在连续生活史阶段的代谢速率与运动耐力，验证血孢子虫感染是否会影响有氧代谢能力。结果显示，无论是实验感染组还是野生组鸟类，急性或慢性感染均未对其静息代谢率、最大代谢率或运动耐力产生显著影响。无论感染组还是未感染组鸟类，从繁殖阶段到迁徙阶段，静息与最大运动状态下的耗氧率以及运动耐力均显著提升。值得注意的是，与迁徙准备相关的表型变化同样不受虫血症（parasitaemia）水平的影响。因此，达到慢性感染典型虫血症水平的迁徙鸟类，其迁徙能力与未感染个体并无差异。由此可见，若感染宿主与未感染同类在迁徙物候上存在差异，其背后的机制应并非有氧代谢能力的改变，而是其他途径。