Young male blackcaps with blood parasite coinfections cope with oxidative stress favouring anthocyanin-rich food during migratory fattening

Parasites may alter host physiology, which may promote behavioural adaptations to counteract their effect. Adaptive feeding may help individuals to cope with infection, especially during physiologically demanding life stages. For instance, migrating birds need fuel for long-distance flights and to repair oxidative damage caused by intense aerobic exercise, and parasites may influence how individuals balance these needs. Infected birds may face increased oxidative challenges, which could induce them to favour antioxidant defences over other needs, such as fattening. We tested whether migrating birds can adaptively choose food according to their needs, favouring dietary antioxidants to cope with oxidative stress caused by haemosporidian blood parasites during migration. During autumn migration, we mist-netted young male Eurasian blackcaps (Sylvia atricapilla) stopping over in central Spain. We placed the birds in cages where they were offered fat and anthocyanin-enriched food alternatives. We measured preference for each food offer. We tested their infections with haemosporidian parasites by PCR techniques and their parasitaemia by blood smear inspection. We also measured physiological variables that account for nutritional and oxidative status in red blood cells and plasma. We found that birds with multiple infections favoured anthocyanin-enriched food controlling for an effect of body mass on food preference (lean blackcaps preferred anthocyanins, likely because they are urged to repair oxidative damage upon arrival on stopover with depleted energy reserves). Haemosporidian-infected birds had a lower antioxidant capacity of plasma, although no effect of infections on oxidative damage was detected, and individuals with more oxidative damage preferred anthocyanin-enriched food. Our results suggest that haemosporidian infections may increase individuals’ antioxidant needs, which could affect migratory performance if the urge to find dietary antioxidants reduces the rate of fuel consumption.

寄生虫可改变宿主生理状态，进而促使宿主产生行为适应性以对抗寄生虫的感染效应。适应性觅食行为能够帮助宿主应对感染，尤其在生理负荷较高的生命阶段中意义重大。例如，迁徙鸟类需要为长途飞行储备能量，并修复高强度有氧运动引发的氧化损伤，而寄生虫会影响宿主对这些生理需求的平衡调控。受感染的鸟类会面临更严峻的氧化应激挑战，这可能促使它们优先保障抗氧化防御相关的资源供给，而非育肥等其他生理需求。本研究旨在探究迁徙鸟类能否根据自身生理需求适应性地选择食物，优先摄取膳食抗氧化剂以应对迁徙期间由血孢子虫（haemosporidian）血液寄生虫引发的氧化应激。在秋季迁徙期间，我们在西班牙中部的中途停歇地，通过雾网捕获了幼年雄性欧亚黑顶林莺（Sylvia atricapilla）。将捕获的鸟类安置于实验笼中，为其提供富含脂肪与花青素的两种备选食物，并记录其对每种食物的选择偏好。我们通过聚合酶链式反应（PCR）技术检测鸟类的血孢子虫感染情况，并通过血涂片镜检量化其寄生虫血症水平。此外，我们还检测了红细胞与血浆中反映营养状态与氧化应激状态的多项生理指标。研究发现，在控制体重对食物偏好的影响后，存在多重感染的鸟类更倾向于选择富含花青素的食物；体况偏瘦的黑顶林莺同样偏好花青素食物，这可能是因为它们在迁徙中途停歇时能量储备耗尽，亟需修复氧化损伤。感染血孢子虫的鸟类血浆抗氧化能力更低，尽管未检测到感染对氧化损伤存在显著影响，但氧化损伤程度更高的个体同样更偏好富含花青素的食物。本研究结果表明，血孢子虫感染可能会提升宿主的抗氧化需求，若因优先寻找膳食抗氧化剂而降低了能量储备的积累速率，则可能对鸟类的迁徙表现产生不利影响。