Serially homologous ears perform frequency range fractionation in the praying mantis, Creobroter (Mantodea, Hymenopodidae)

Abstract

Unlike most praying mantises that have a single region of auditory sensitivity, species in the genus Creobroter have equally sensitive hearing at 2–4 and at 25–50 kHz and and are relatively insensitivity at 10–15 kHz — they have a W-shaped audiogram. Ultrasonic sensitivity originates from an auditory organ in the ventral midline of the metathorax that closely resembles the ear of other mantises. Ablation experiments demonstrate that low frequency sensitivity derives from a serially homologous mesothoracic auditory organ. Extracellular recordings suggest that these two ears operate largely, if not entirely, independently of one another in the thorax. The low frequency response has a longer latency, more action potentials per stimulus, and different patterns of change with increasing SPL than the high frequency response. Separate interneurons mediate responses in the two frequency ranges, but our evidence suggests that they are two serially homologous sets of cells. Neither auditory organ shows any physiological evidence of directional sensitivity. Ultrasound triggers a set of behaviors in flying hymenopodid mantises much like those in other mantises, but the behavioral significance of low frequency hearing in these animals is still unknown.