DISSERTATION RESEARCH: Investigating Genomic Signatures of Range Shifts and Demographic Change in Migratory Hummingbirds

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Range shifts and changes in population size are thought to be common features of evolution in animals, in part because most species are older than recent ice ages and have persisted through dramatic changes in global climate and land cover. Migratory birds present particularly interesting case studies in this context: they are capable of crossing huge geographic areas in search of newly suitable habitats, but their potential for adaptation to new areas may be limited by genetic cues determining the direction and timing of migration. Recent efforts to forecast species' ranges under an assortment of climate change scenarios suggest that most bird species in North America will need to shift their ranges in order to persist in the climatic conditions they experienced during the past century. Understanding the dynamics of range shifts and their long-term impacts on species' evolutionary potential is thus an important task for biologists in the 21st century. This project is focused on uncovering the temporal and spatial dynamics of shifts in demography and range in the Bee hummingbirds, a young radiation including all migratory hummingbirds breeding in temperate North America. Hummingbirds are good subjects for studies of range and demography because their extreme physiologic constraints, nectivorous diet, and high dispersal abilities suggest that they are sensitive to shifts in regional climate and phenology. In addition, two of the project's focal species - Selasphorus rufus and Calypte anna - have experienced dramatic range shifts over the last 100 years, offering a chance to study the process of colonization and expansion in contemporary time. This project applies population-genomic analyses of reduced-representation DNA sequencing libraries to examine response to environmental change by (1) determining the role of founder effects and gene flow in establishing populations in novel ranges over the last century, (2) testing for genetic divergence and reduced gene flow across migratory divides, and (3) comparing demographic responses to Pleistocene climate change in a multispecies comparative framework along a latitudinal gradient.