UC Santa Cruz

Integrating ecology and genetics is necessary to build holistic understanding of how new species form. Speciation requires genetic divergence, which frequently occurs as populations adapt to different environments. Adaptation to one environment frequently trades-off with adaptation to another environment. This can result in ecogeographic isolation, in which species are isolated by the inability to co-occur and the geographic separation of their environments. When ecogeogrpahic isolation occurs over relatively small distances, hybridization can occur between the deferentially adapted species. Hybridization can open the door to gene flow between species, which can ultimately break down species distinctions. However, there are numerous examples of species remaining distinct despite gene flow. How is this possible? To answer this question, I combine ecology, physiology, and genetics to build understanding of differential adaptations, trade-offs, and patterns of gene flow in two recently diverged spiral ginger species that remain distinct despite hybridizing.

In chapter one, I generate and compare two new spiral ginger reference genomes. These genomes expand resources for genetic investigation of rapid tropical plant speciation and facilitate analyses in chapter 4. In chapter 2, I describe the mechanism of drought adaptation that facilitates strong ecogeographic isolation between my focal species. In chapter 3, I characterize trade-offs between investment in growth and defense between the two species, how the trade-offs relate to drought adaptation, and how they facilitate ecogeographic isolation. In chapter 4, I describe patterns of gene flow between my focal species through time and across the genome, then compare the general patterns to preliminary genetic maps of the regions controlling key differentiating traits. Together, these chapters elucidate how divergent adaptation to abiotic and biotic environmental conditions can enable gene flow that does not eliminate species distinctions.