Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Elizabeth MacDougall-Shackleton


Local adaptation is the result of natural selection operating at a local scale, such that trade-offs in fitness across different environments result in individuals having higher fitness in their place of origin than when transported into a foreign environment. Populations may become locally adapted to features of their abiotic environment, or in the case of coevolutionary arms races between hosts and parasites, to other species comprising their biotic environment. If host populations are adapted to their local (sympatric) parasites, or conversely if parasites are adapted to their local hosts, then interactions with local parasite strains may influence the fitness consequences of host dispersal. I investigated the ecological and evolutionary impact of haematozoan parasites (genera Plasmodium, Leucocytozoon, Haemoproteus) on song sparrow (Melospiza melodia) hosts. I hypothesized that song sparrows have an advantage in defending against local parasite strains, resulting in parasite-mediated selection against natal dispersal. I predicted that condition and survivorship should correlate positively with philopatry, and that such 'home-field advantage' is mediated by enhanced ability to deal with sympatric parasites. I used genetic assignment tests to quantify natural variation in philopatry, and asked whether song sparrows of local origin showed a home-field advantage over immigrants, across multiple populations (Chapter 2). I compared population genetic structure of hosts and parasites to test for coevolution (Chapter 3). I attempted to experimentally reduce parasite load, to test if malarial parasites decrease territorial defense (Chapter 4). Finally, I used a cross-infection design to compare resistance to sympatric versus allopatric strains of Plasmodium (Chapter 5). Song sparrows of local origin tended to have lower parasite loads in the wild. Moreover, sparrows were less likely to become infected when experimentally inoculated with a sympatric than an allopatric Plasmodium lineage. Population genetic structure of song sparrows was generally not correlated to that of parasites, but I found similar genetic structuring between song sparrows and one Plasmodium taxon. Interactions with haematozoan parasites may influence the fitness consequences of dispersal by song sparrows. This has implications for the evolution of dispersal, patterns of biodiversity, and conservation in an era of emerging infectious disease.