Evolution of the causes of speciation: comparative analysis of genomic variation and the genetic basis of traits responsible for diversification

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Understanding speciation, the splitting of one species into two, is essential for our understanding of biodiversity and sound conservation policy. My research group has made key discoveries regarding speciation, using model systems of birds and salamanders of western Canada as well as other regions of North America and Eurasia. Given our prior research on a variety of species complexes (i.e. groups of closely related species or subspecies that hybridize where they meet), we are now well poised to conduct pioneering research on the relationship between patterns of genomic evolution (i.e. changes in DNA) and patterns of trait differentiation and reproductive isolation among populations. During the next five years, we will conduct research that advances our long-term research goal: developing a comprehensive understanding of the dynamics of speciation in land-dwelling vertebrates, especially within long-distance migratory birds. Our short-term goals include: G1) Conducting in-depth analysis of the genetic basis of seasonal migratory orientation and its role in speciation. Our previous work showed that hybrids between two forms of Swainson's thrush have intermediate migratory routes and that this behavior appears to be due to variation in a particular genomic region on chromosome 4. We will investigate this in more depth using a hybrid zone (and migratory divide) between two forms of warblers. G2) Testing whether there are specific genomic regions that tend to spread throughout species complexes before becoming differentiated between groups. This newly developed idea, which we call “sweep before differentiation,” is consistent with evidence in at least two species groups under examination, and differs dramatically from existing theories for what regions become different between species. G3) Examining whether there is coevolution between two distinct types of genetic material: mitochondrial DNA and nuclear DNA. If so, such coevolution can cause low fitness in hybrids and contribute to speciation. G4) Determining whether patterns of genomic differentiation during speciation tend to be more similar between species groups that are closely related (e.g. two species groups of warblers), in contrast to more distantly related species groups (e.g. warblers versus woodpeckers). Such a pattern would point to common causes of speciation within certain groups, and would show that speciation itself can be viewed as something that evolves over time. G5) Developing hybrid zone theory and its application to species conservation. Many species hybridize with other species, yet there is not consensus regarding the implications of hybridization for species concepts and conservation policy. We will contribute to a consensus by expanding hybrid zone theory and conducting a review of empirical patterns of genomic differentiation across hybrid zones and their implications for effective conservation.