Short-term and long-term consequences of avian malaria-like infection

寄生虫和病原体在个体生理和群体进化层面上引起并维持宿主防御机制的巨大多样性。防御可以分为两大部分——抗性和耐受性，但耐受性的机制尚不清楚，特别是对于各种各样的野生动物感染，它们对宿主的伤害不是很明显。特别是对于具有儿童疾病生活史特征的早期、垂直和准垂直传播感染，预计将进化出低寄生虫毒力和高宿主耐受性。一个突出的例子是类似疟疾的寄生虫，它们感染并塑造了许多野生哺乳动物、蜥蜴和鸟类宿主的生活史。对于这些寄生虫，感染的时间和宿主-寄生虫共同进化的不同结果尚未被探索到它们的生理表达，并且感染宿主的成本是未知的。本研究旨在在一个野生动物模型系统中探索所有这些方面，并量化疟疾样感染对野生猛禽雏鸟生理和转录组谱的短期影响，以及感染对生存和招募的长期影响。这将在一项长期实地研究的基础上实现，该研究在过去14年中对一群普通秃鹫（Buteo Buteo）的所有雏鸟进行了抽样调查，其中44%的雏鸟感染了与疟疾有关的寄生虫白血细胞原虫。虽然大多数雏鸟在幼年时就已经感染了白细胞原虫，但没有明显的致病死亡率。感染的生理和长期成本将通过使用抗疟疾药物对受感染雏鸟群体进行实验性治疗来量化，跟踪它们的发育并量化它们的生理和转录组特征，直至雏鸟羽化。感染的影响可能还取决于宿主表型和环境条件，如营养压力。因此，白细胞原虫感染与秃鹰羽毛形态和猎物可得性的协同效应将在单独的感染缓解实验中进行分析。与未感染和处理过的宿主相比，受感染宿主的转录组谱将显示对寄生虫反应的个体耐受性与抗性的比例。在研究期结束时，感染和感染缓解的翅膀标记雏鸟的累积样本将为分析感染依赖的长期生存提供足够的数据。这项关于猛禽雏鸟疟疾样感染的研究提供了独特的机会，以经验显示共同进化的儿童疾病对宿主耐受性和寄生虫毒力的影响。

Parasites and pathogens cause and maintain a great diversity of defence mechanisms of their hosts, both on the levels of individual physiology and population-wide evolution. Defences can be separated in two large fractions – resistance and tolerance, but the mechanisms of tolerance are poorly understood, especially for the wide variety or wildlife infections which are not very obviously harming their hosts. Particularly low parasite virulence and high host tolerance are expected to evolve for early, vertically and quasi-vertically transmitted infections, which have the life-history features of childhood diseases. A prominent example are malaria-like parasites, which infect and shape the life-histories of many wild mammalian, lizard and bird hosts. For these parasites, the timing of infection, and the different outcomes of the host-parasite co-evolution have not been explored to their physiological expression, and the costs of infection to the hosts are unknown. This proposal aims to explore all these aspects in one wildlife model system and quantify the short-term effects of malaria-like infections on the physiology and transcriptome profiles of wild raptor nestlings, as well as the long-term effects of the infection on survival and recruitment. This will be achieved on the basis of a long-term field study, which has been sampling all nestlings in a population of common buzzards (Buteo buteo) for the last 14 years and where 44% of all nestlings are infected by the malaria-related parasite Leucocytozoon buteonis. Although most nestlings are already infected with Leucocytozoon at an early age, there is no obvious disease-caused mortality. The physiological and long-term costs of the infection will be quantified via experimental treatment of groups of infected nestlings with antimalarial drugs, following their development and quantifying their physiological and transcriptomic profile until fledging. The effects of infection may additionally depend on the host phenotype, and on environmental conditions such as nutritional stress. Therefore the synergistic effects of Leucocytozoon infection with buzzard plumage morph and prey availability will be analysed in separate infection-relief experiments. The transcriptome profiles of infected, compared to non-infected and treated hosts, will show the individual ratio of tolerance to resistance in the response to the parasite. By the end of the study period the cumulative sample of infected and infection-relieved wing-tagged nestlings will deliver sufficient data for analysis of infection-dependent long-term survival. This study on malaria-like infections of raptor nestling gives the unique opportunity to empirically show the effects of coevolved childhood diseases on host tolerance and parasite virulence.