Phylogeny and the evolution of acoustic communication in extant Ensifera (Insecta, Orthoptera)

Ensifera present an appropriate and interesting model for the study of acoustic communication, because of their diverse signal and communication modalities, and due to their accessibility for field and laboratory studies. Several hypotheses have been proposed to explain the acoustic evolution of Ensifera, but they were elaborated without any reference to a falsifiable phylogeny, and were consequently highly speculative. Similarly, phylogenetic relationships between ensiferan clades have not hitherto been studied using modern standard methodology, and the sole cladistic analysis by Gwynne in 1995 was methodologically flawed. No sound hypothesis therefore currently exists for ensiferan phylogeny, which precludes historical analysis of their communication modalities. In the present paper, the phylogeny is established on the basis of morpho‐anatomical characters and used to analyse the evolution of acoustic communication in this clade by mapping the characters related to auditory and stridulatory structures onto the resultant trees. Cladistic analyses resulted in two equi‐parsimonious cladograms (length 154, C 64, CI 58, RI 61) with the following topologies: (1) [(Grylloidea–Gryllotalpidae) (Rhaphidophoridae (Schizodactylidae (Gryllacrididae ((Stenopelmatidae–Cooloola) (Anostostomatidae (Prophalangopsis (Cyphoderris (Tettigoniidae–Lezina))))))))] (2) [(Grylloidea–Gryllotalpidae)(Rhaphidophoridae (Schizodactylidae (Gryllacrididae–Cooloola–(Stenopelmatidae (Anostostomatidae (Prophalangopsis (Cyphoderris (Tettigoniidae–Lezina))))))))]. According to these topologies, Ensifera were ancestrally devoid of acoustic and hearing systems. An acoustic (tegminal or femoro‐abdominal) apparatus appeared a number of times independently with convergent structures. Similarly, tibial tympana developed several times independently. Moreover, four hypotheses (each according to a definite pattern of character transformation) can be proposed to explain the evolution of acoustic communication in the different ensiferan clades and relate it to a definite communicatory context. These hypotheses do not apply equally to ensiferan subclades. Grylloidea and Gryllotalpoidea could have experienced convergently a direct development of an intraspecific acoustic communication. Acoustic communication in Tettigoniidea has evolved more ambiguously, and may either have resulted from a direct evolution analogous to that having occurred in Gryllidea, or have developed in a completely different behavioural context. Future studies of acoustic communication in the different ensiferan clades will have to take into account the fact that the involved structures most often are not homologous and that their evolution may not have taken place in similar conditions. Different hypotheses of acoustic communication evolution may apply to different clades, and there may be no single explanation for acoustic communication in Ensifera.