The North American gray treefrog complex (Hyla versicolor sensu lato), defined here as encompassing the diploid species Hyla chrysoscelis and Hyla avivoca, and the tetraploid Hyla versicolor, has long been used as a model system in a variety of biological fields. Although the origins of polyploidy in this group have been extensively studied since the discovery of polyploidy exactly 50 years ago, the most recent studies on this topic come to considerably different conclusions. Furthermore, though the biogeography of this system has been extensively discussed, no study to date has investigated the biogeography of gray treefrogs explicitly. These doubts and lack of knowledge affect the interpretation of studies utilizing gray treefrogs, and as the only known anuran polyploid complex in North America, it is of general interest that the origins and biogeography of this system are explored further. Finally, because work on this system has been foundational for defining our understanding of acoustic communication and mate choice, it is imperative that we investigate the evolutionary history of acoustic communication in gray treefrogs. In this dissertation, I present my work in defining the evolutionary history, origins of polyploidy, biogeography, and the evolution of acoustic communication in gray treefrogs. In addition to this research, I also present a historical review of the systematic and evolutionary work that has defined this system over the last two centuries. In the next chapter, I define the evolutionary history of the polyploid gray treefrog complex---utilizing hundreds of loci to estimate the taxonomic relationships, the origins of whole genome duplication (WGD), the mode of polyploidization, the history of hybridization, and the timing of important evolutionary events. In the following chapter, utilizing the data and results from the previous chapter along with a large acoustic data set collected over 45 years that includes >1500 individual frogs, I estimate the biogeography and evolutionary history of acoustic communication of this system. This dissertation adds to the rich history of evolution research in this system, and in general, aims to clarify the evolutionary history of gray treefrogs throughout the Quaternary. I find strong evidence for a recent autopolyploid origin of H. versicolor from a single WGD event. I also uncover significant hybridization in this complex, and show that historical hybridization has led to the formation of additional polyploid lineages following mitochondrial capture. My biogeographical analysis demonstrates that the origin of WGD occurred near the limit of the Laurentide ice sheet from the Illinoian glacial period that preceded my estimated WGD timing, and that glacial cycles have played a significant role in the evolution of this system. Finally, my acoustic analysis demonstrates the diversity of calls in H. chrysoscelis are associated with expansions out of glacial refugia, and that unique calls in H. versicolor are associated with a mitochondrial introgression event.
