Reconstructing Radiations: genomics of diversification in lizards and butterflies

Abstract

Understanding the processes that lead lineages to diversify and give rise to new species is a major driving question in evolutionary biology. The role of extrinsic forces, such as geographic isolation and environmental variation, are both considered important by preventing gene flow, either due to physical barriers that impede migration or due to local adaptive divergence. In this dissertation, I investigate how environmental variation and geographic isolation have contributed to diversification within two model clades for evolution and ecology research: Anolis lizards and Heliconius butterflies. Using genome-scale data from hundreds of individuals, I reconstruct the evolutionary histories of these two byproducts of recent divergence and explore patterns of genomic variation to ask how geographic isolation and varying environmental conditions have shaped those histories. First, I focus on the role that environmental variation has played in shaping genomic patterns of divergence among lizards characterized by discordant phenotypic and genetic variation. I find population genomic structure largely corresponds to broad-scale environmental variation on the island of Hispaniola, but show that efforts to detect genomic regions underlying local adaptation are limited by available genomic resources and current methods. Second, accessing much greater breadth of the genome, I reconstruct the evolutionary history of a wide-ranging butterfly found across continental and island habitats to test whether geographic isolation has driven divergence. By using a species tree inference approach, I show that previously inferred phylogenetic relationships may have been confounded by rapid divergence, and find isolated populations to be divergent from their mainland counterparts. Together, these chapters advance our knowledge of the role played by extrinsic forces in shaping genome-wide variation in lineages undergoing divergence.