UBC Theses and Dissertations

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UBC Theses and Dissertations

Hybridization, speciation and the biogeography of genetic and phenotypic variation in Setophaga warblers Toews, David P. L.


Contact zones between previously isolated taxa provide natural systems for studying the processes involved in divergence, adaptation and reproductive isolation. In this thesis I use inferences drawn from biogeographic patterns and the characteristics of hybrids to understand the evolutionary processes involved in the production and maintenance of avian contact zones. In chapter two, I use genetic and phenotypic data from two related species of wood warbler to study the hybridization dynamics between them. I found that Setophaga virens and S. townsendi hybridize extensively where they come into contact but that the hybrid zone between them is narrow, suggesting moderate selection against hybrids. In chapter three and four I examine a possible mechanism of selection within such hybrid zones: differences in seasonal migratory behaviour. I explore this in a hybrid zone between S. coronata and S. auduboni. In chapter three I use isotopic data from breeding birds to make inferences about the wintering behaviour of hybrids. In chapter four, I use genetic data and video-based orientation assays of birds on fall migration to estimate the migratory tendency of birds in the hybrid zone. I found that (1) isotopes suggest that birds in the hybrid zone mostly wintered in the southeastern U.S. and (2) birds, on average, oriented towards the northeast during fall migration, regardless of their genetic background. These hybrid zones illustrate patterns of concordance between some characteristics but discordance in others. As I review in chapter five, the biogeographic patterns associated with discordant molecular markers, especially between those in the nuclear versus mitochondrial genome, can reveal novel insights into important evolutionary processes. In chapter six I address an example of such discordance, where previous research has suggested that mitochondria from S. coronata have introgressed throughout much of the range of S. auduboni. I use genetic, biochemical, and phenotypic variation to show that this shift in mitochondria is correlated with a shift in migratory behaviour and with some aspects of mitochondrial phenotype. In chapter seven, I use a genome-wide assay of tens of thousands of nuclear polymorphisms to test whether mtDNA is truly an outlier as compared to the nuclear genome.

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Attribution-NonCommercial-NoDerivs 2.5 Canada