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

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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.