Comparative genomic analysis of hybridization and speciation: uncovering genes and traits responsible for diversification

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There is abundant evidence for the process of speciation, whereby a single species evolves into two, but the selective forces that drive this process are under much debate. Hybrid zones, regions where different but related species come into contact and interbreed to some extent, provide excellent opportunities to determine which traits are most involved in speciation. Western Canada has many hybrid zones between distinct western and eastern forms of birds that evolved differences while they were separated in different southern regions during the Ice Ages. Across a number of different hybrid zones, we will study variation in a variety of traits, determining which traits show the sharpest change across each zone; these are likely the traits most involved in speciation. We will also use a recently developed method of genetic analysis called next-generation DNA sequencing to identify genes associated with traits of interest. To understand the location of these genes in the genome (e.g., on what chromosome), we will use next-generation sequencing to assemble the genome of one reference individual for each hybrid zone. One important trait is seasonal migration. Many pairs of western and eastern species differ dramatically in the routes that they take from their breeding ranges to their wintering ranges. We hypothesize that hybrids have intermediate migratory orientations and suffer lower survival as a result. We will determine orientation behavior of birds in each hybrid zone using tracking devices and orientation cages, and will determine the genetic regions associated with differences in migration. Our work will also (1) use genomic analysis to reconstruct the history of several species that may have arisen through hybridization of other species, and (2) test whether there are certain key genomic regions, such as the sex chromosomes, that play a strong role in speciation within birds. By generating assembled genomes and gene-trait association studies in six groups of hybridizing species, we will contribute much knowledge toward future studies of the genetic basis of adaptation and speciation.