Haemoproteus parasites and passerines: the effect of local generalists on inferences of host-parasite co-phylogeny in the British Isles

Host-parasite associations provide a benchmark for investigating evolutionary arms races and antagonistic coevolution. However, the potential ecological mechanisms underlying such associations are difficult to unravel. In particular, local adaptations of hosts and/or parasites may hamper reliable inferences of host-parasite relationships and the specialist-generalist definitions of parasite lineages, making it problematic to understand such relationships on a global scale. Phylogenetic methods were used to investigate co-phylogenetic patterns between vector-borne parasites of the genus Haemoproteus and their passeriform hosts, to infer the ecological interactions of parasite and host that may have driven the evolution of both groups in a local geographic domain. As several Haemoproteus lineages were only detected once, and given the occurrence of a single extreme generalist, the effect of removing individual lineages on the co-phylogeny pattern was tested. When all lineages were included, and when all singly- detected lineages were removed, there was no convincing evidence for host-parasite co- phylogeny. However, when only the generalist lineage was removed, strong support for co- phylogeny was indicated, and ecological interactions could be successfully inferred. This study exemplifies the importance of identifying locally abundant lineages when sampling host- parasite systems, to provide reliable insights into the precise mechanisms underlying host- parasite interactions.