"Pathogens, mate choice and gene flow in songbirds"

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Parasites represent nearly half of all known species and have important effects on the fitness of host individuals. A major goal of this research program is to understand how bloodborne parasites affect the evolutionary potential of their songbird host populations. Because genetically diverse ("outbred") hosts are thought to be able to resist a broader array of infectious disease than are more inbred individuals, one possibility (the "parasites-as-connectors" hypothesis) is that parasites promote gene flow and inbreeding avoidance, and thereby maintain high levels of host genetic diversity. Alternatively, another possibility (the "parasites-as-wedges" hypothesis) is that host adaptations to local parasites reduce gene flow between populations and promote inbreeding, resulting in the loss of host genetic diversity. To distinguish between these alternatives, my research combines intensive and long-term field study of the behaviour and ecology of wild-breeding songbirds with genetic analyses and immune challenges. A second, complementary, line of research focuses on the role of learned birdsong in connecting or in isolating populations. In songbirds, song is learned during early life and may thus reflect the singer's population of origin. This provides a potential behavioural cue for inbreeding or outbreeding. With human activities increasingly fragmenting natural habitats and isolating natural populations, it has become critical to identify and understand the factors that protect or erode genetic diversity in the wild. Predicting how parasites influence host evolution is particularly important in light of newly emerging infectious diseases associated with a changing climate.