Unlocking the genomics of species formation in Amazonian and high-latitude birds

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My research investigates why the tropics harbor an extraordinary number of species in comparison with high latitudes. A key theory links high tropical richness to accelerated speciation-the formation of new species-yet our understanding of the biogeographic drivers of speciation and the length of time to complete speciation in biodiverse tropical regions remains rudimentary. The goal of this proposal is to harness the power of genomic data to determine the biogeographic processes that drive avian speciation in the most species-rich region of the planet-the Amazon basin-and to test whether the length of time required to complete speciation is shorter there compared to species-poor communities of Canada. Wide rivers are known to be effective barriers for understory birds over much of Amazonia and represent the most probable biogeographic barriers promoting Amazonian speciation. Yet our recent work demonstrated rivers cease to be effective dispersal barriers in headwater regions of the Amazon periphery, where species readily cross narrow river channels and hybridize. However, during glacial periods forests retracted out of headwater regions and large rivers may have been effective barriers driving speciation. To test this theory, our first set of projects will look for the expected genomic signatures of changes in population size and recent range expansion into headwater regions across a series of avian species. Following their isolation by geographic barriers, populations begin to accumulate genetic differences, culminating in reproductive isolation: the inability to produce successful offspring with each other. Reproductive isolation marks the endpoint of speciation. The second set of projects will sequence whole genomes and study hybridization to test the evolutionary speed at which reproductive isolation evolves in tropical versus high-latitude regions. My lab will quantify how species' genomes resist becoming homogenized between species through interbreeding at hybrid zones-geographic regions where diverging species come into contact and interbreed. Each hybrid zone provides a snapshot in time of the speciation process, with cessation of genomic homogenization between species occurring once reproductive isolation is complete. By analysing avian hybrid zones between 22 species pairs, varying from a few hundred thousand to over four million years in evolutionary age, we will determine whether the timeline to reproductive isolation is faster in Amazonia, as expected if rapid speciation drove high species richness. We will also sequence high-quality reference genomes for 15 pairs of sister species in Canada and 15 in the Amazon and compare rates at which genomes acquire chromosomal rearrangements. These rearrangements have been implicated as important in generating reproductive isolation. Together, these large-scale comparative projects will enable my lab to test the role of speciation in contributing to the Amazon's high species richness.