Evolution of parasite island syndromes without long-term host population isolation: parasite dynamics in Macaronesian blackcaps Sylvia atricapilla

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Aim: The study of parasite biogeography on islands is important for our understanding of both the processes involved in the evolution of parasite assemblages worldwide, and the ecology and conservation of insular communities. By studying the haemosporidian blood parasites of a bird that has recently colonised a number of oceanic islands, we were able to test hypotheses relating to the processes involved in parasite colonization and community assembly prior to the permanent isolation of host species on islands. Location The Atlantic Ocean archipelagos of Madeira and the Canary Islands. Methods: We used cytochrome b DNA sequences to determine the prevalence and richness of parasites of the genera Haemoproteus, Plasmodium and Leucocytozoon in blackcaps, Sylvia atricapilla, a widespread passerine which colonized these Atlantic archipelagos during the Last Glacial Maximum. We compared insular blackcap parasite assemblages with those observed in 37 blackcap populations sampled on mainland Europe. Results: The insular parasite assemblage was impoverished, containing ca.10% of the parasites found on the continent.None of the parasites observed on the islands were blackcap specific. Some of the observed parasites appear to have switched from blackcaps to other Macaronesian host species, while others were of Afrotropical origin and were acquired after blackcaps colonised the islands. The prevalence of parasites in the island populations of blackcaps was lower than in mainland blackcap populations and parasite richness decreased with increasing island distance to the continent. Main conclusions: Macaronesian blackcaps do not face the strong parasite load encountered by their mainland counterparts despite the fact that blackcap migration 3 from the continent may directly transport mainland blackcap parasites to the islands. These results support the idea that normal mainland host-parasite associations are compromised on islands, and that parasite island syndromes (low richness, frequent host-switching, and reduced specialization) evolve even before insular host populations become completely isolated from their mainland counterparts.