The spiny devil katydids, Panacanthus Walker (Orthoptera: Tettigoniidae): an evolutionary study of acoustic behaviour and morphological traits

A cladistic analysis and systematic revision of the genus Panacanthus accompanies the description of three new species, with calling songs reported for four species. The evolutionary origin of spines is considered as a defensive mechanism in Panacanthus; both morphological and behavioural (i.e. acoustic) traits allow inferences about relationships. Phylogenetic analysis produced one most parsimonious cladogram eighty‐two steps long, with the ensemble consistency index = 0.84. Panacanthus cuspidatus and P. pallicornis (formerly Storniza Walker 1869, Martinezia Bolivar 1881) are properly incorporated in Panacanthus. On morphology, Panacanthus is more related to the Neotropical Copiphora and Lirometopum than to the Old World Lesina. Character analysis reveals that in Panacanthus the ancestral condition of calling song resonance (the production of musical sounds) has given rise to a more nonresonant (transient) stridulation. A correlation between the production of more complex sound waves and spinous protection of the body (especially the pronotum) is noted. Because early workers grouped Panacanthus with other spiny genera, based on pronotal morphology, we present a critique of the evolutionary and ecological implications of the development of defensive spines in this genus. This approach may be applied to other taxa using a similar protective mechanism. We advise against arrangement of the pronotal, cephalic and femoral armature as a homologous characteristic across subfamilies. Several pronotal processes and modifications evolved independently in other genera of Conocephalinae, Hetrodinae, Pseudophyllinae and Phaneropterinae. The pronotal structure of Panacanthus is unique and may be taken as a synapomorphic characteristic of all its species and as an autapomorphic feature of the genus.