Evolution and Speciation in North American Toads

Abstract

Understanding speciation, the evolutionary process by which new species evolve, is a central goal of evolutionary biology. Yet many important questions regarding this process remain unanswered. In this dissertation, I investigate speciation within North American toads in the genus Anaxyrus, a group belonging to the family Bufonidae, which has been the focus of many studies on speciation. I integrate data from hybrid zones, range-wide sampling of species in the genus, and simulations to illuminate patterns of diversification. I provide the first genetic characterization of two putative hybrid zones and demonstrate that both ancient and ongoing introgression is substantial. I also show that previous inferences of the evolutionary relationships among species of Anaxyrus have been unable to accurately reconstruct the true history of this group. With a better representation of the evolutionary history of these species, I obtain estimates of the timing of events and discuss the consequences of these findings as they relate to diversification and hybridization in Anaxyrus. Finally, I show through simulations that commonly used methods in evolutionary biology suffer from violations of assumptions we make about the evolutionary process. This highlights the need for caution when interpreting results and continued evaluation of the performance of methods in real-world scenarios. This study significantly enhances our understanding of speciation in Anaxyrus as well as the promise of this group for furthering our understanding of this fundamental evolutionary process.