Biomechanics of musical stridulation in katydids (Orthoptera: Ensifera: Tettigoniidae): An evolutionary approach

Stridulation in Ensifera has been studied from different points of view: physiological, mechanical, behavioural. Most of the available literature focuses on crickets with regards to which most of these aspects of stridulation have been satisfactorily discussed. Herein I explore the biomechanical properties of the forewings in Tettigoniidae (katydids) and compare the mechanical features of the sound producing organ across this family, focusing on those species using pure tone songs. The first chapter includes a general introduction and methodology. The other five chapters are based on data that I collected.; Chapter Two explores the theoretical basis of the four mechanisms of stridulation used by katydids and illustrates them with real examples. This chapter also presents a model of stridulation used by some species, in which the song is given in pulse trains at frequencies of <30 kHz.; Chapter Three, a cladistic analysis of the genus Panacanthus , reveals that the ancestral condition of calling song resonance (the production of musical sounds) evolved into a more nonresonant (transient) stridulation in some species of this genus.; The fourth chapter deals with the biomechanics of stridulation in Panacanthus pallicornis, a species that generates sustained pulses and musical songs. In this chapter, I propose a mechanism for resonant stridulation in katydids involving coherent pulses. Unlike crickets, katydids (which have asymmetric forewings) do not need an escapement mechanism that regulates the movement of the scraper across the stridulatory file and allows the production of coherent pulses.; Chapter Five involves a comparative study across extant tettigoniid species that use pure tones. These species employ frequencies in the audio range (<20 kHz), in the moderate ultrasonic range (20-40 kHz), or in the extreme ultrasonic range (>40 kHz). Extreme high frequency singers use elastic energy to generate very high pure tones as an strategy to reduce the speed of muscle contraction during stridulation which requires high demands of energy; this mechanism becomes important when the frequencies used exceed ∼40-45 kHz. This mechanism of stridulation is discussed and illustrated.; In the final chapter and based on a comparative analysis of the stridulatory organs across the Tettigoniidae, I propose a model to explain a remarkable characteristic of most katydids: asymmetric forewings.