Trees, leaves, and lobes: Katydid (Orthoptera: Tettigoniidae) phylogenetics, leaf-like wings, and external ear morphology

Tettigoniidae has a cosmopolitan distribution and is comprised of more than 6500 species making katydids the second largest family within the order Orthoptera. Tettigoniid popularity has come from the songs males use to attract mates. Katydids hear these calls via a system of tibial tympana (ears) connected internally to an auditory spiracle on the thorax. Cuticular folding around the ears is common. Morphology associated with katydid hearing is currently used to diagnose subfamilies. Tettigoniids are also well recognized for their defense systems, including leaf-like wings for protection via crypsis, aposematic coloration, thick protective spines, and Batesian mimicry. However, little is known about katydid phylogenetic relationships and many subfamilies are probably paraphyletic. Previous studies have been limited in taxon sampling and rely heavily on intuition. To test the monophyly of katydid subfamilies and determine the evolutionary patterns in katydid ear morphology and defenses we sequenced 6 genes (18S, 28S, H3, Wingless, COII, and TUBA) from 175 taxa and reconstructed a phylogenetic tree. Ear morphology and defenses were mapped onto the Maximum Likelihood topology. Five subfamilies, including three of the largest (Pseudophyllinae, Tettigoniinae, and Meconematinae), are paraphyletic. Ear morphology and the size and position of the auditory spiracle are homoplasious suggesting 3 independent origins of the small exposed thoracic spiracle. Leaf-like wings are also homoplasious in many tropical katydids with at least 6 origins. This study provides the framework allowing for a larger investigation into katydids and the evolution of complex acoustic signaling.