Cheek, Rebecca G., authorGhalambor, Cameron K., advisorFunk, W. Chris, advisorSillett, T. Scott, committee memberAubry, Lise M., committee member2024-05-272025-05-202024https://hdl.handle.net/10217/238474A fundamental goal of evolutionary biology is to understand the mechanisms that maintain adaptive diversity. This dissertation focuses on the interplay of two key evolutionary mechanisms - natural selection and gene flow. While natural selection is often portrayed as a driving force of adaptive evolution, gene flow is assumed to disrupt selection by introducing maladapted alleles into locally adapted populations. Yet this paradigm is beginning to shift as a growing appreciation for the role gene flow may play in concert with natural selection to facilitate adaptative divergence. I explore this interaction of selection and gene flow in island scrub-jays (Aphelocoma insularis), a highly mobile bird experiencing local adaptation at a microgeographic scale. First, I demonstrated that observed differences in bill morphology between pine-oak ecotones are likely genetically based despite overall limited population genetic structure. Second, I found that the genetic underpinnings of divergent bill morphologies are highly parallel at higher genetic levels, which is indicative of selection acting on shared, but highly polygenic, molecular pathways. Finally, I tested alternate dispersal mechanisms potentially impacting patterns of limited gene flow and found evidence for sex-biased natal habitat preference shaping limited dispersal. Collectively, these results show how gene flow can enhance adaptive divergence at microgeographic scales.born digitaldoctoral dissertationsengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.divergent selectiongenome-wide associationSanta Cruz Island Californiagene flowAphelocoma insularisgenotype-environment associationTextEmbargo expires: 05/20/2025.