Tettigoniidae (katydids) has more than 7200 species and is the largest family within the insect order Orthoptera. Their unique biology including leaf-like crypsis, acoustic signaling, and courtship rituals garners much of their academic attention. However, the taxonomy of katydids is chaotic and previous to these studies, little work had been done to decipher the phylogenetic relationships within this family. Without a robust phylogenetic framework, questions regarding the evolution of katydid disguises including the leaf-like crypsis cannot be addressed. This dissertation contains three chapters. Chapter 1 provides the first phylogenetic hypothesis focusing on Tettigoniidae. In this chapter we show a character thought to be taxonomically informative, the thoracic auditory spiracle, is homoplasious within Tettigoniidae. We provide evidence that the leaf-like wings of katydids have been derived independently in multiple lineages. Additionally, in Chapter 1 the problematic taxonomy within Tettigoniidae, particularly the lack of monophyly in many of the larger and widespread subfamilies, is addressed. Chapter 2 contains a more in depth look into the evolution of crypsis. Leaf-like wings are common throughout Tettigoniidae, but the definition of leaf-like has varied by author. In this second chapter we provide a ratio method for differentiating between leaf-like and non leaf-like wings. Our ratio method was then verified using geometric morphometics. We found at least 15 independent derivations of leaf-like wings in Tettigoniidae. Furthermore we found that throughout Tettigoniidae the leaf-like wings are not a driver of speciation and selection may favor a shift away from the leaf-like wings. Within the cosmopolitan Phaneropterinae, the trend differs, as there is no significant difference between the speciation and transition rates of the leaf-like and non leaf-like lineages. Chapter 3 presents the largest and most comprehensive phylogeny for Tettigoniidae to date and provides a hypothesis for origins and biogeographic dispersal of katydids. Characters that define subfamilies are similar due to similar selective pressures and are not taxonomically informative. As a result, many of the larger and widespread subfamilies, particularly those with species in similar but geographically distant habitats, are paraphyletic. In this chapter we also provide temporary names to define the two large clades containing the bulk of Tettigoniidae diversity (tettigonioid clade and phaneropteroid clade) in addition to smaller subfamily groups to simplify discussion of katydid relationships until a higher-level taxonomic revision is completed.

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