SERIALLY HOMOLOGOUS EARS PERFORM FREQUENCY-RANGE FRACTIONATION IN THEPRAYING-MANTIS, CREOBROTER (MANTODEA, HYMENOPODIDAE)

Unlike most praying mantises that have a single region of auditory sen sitivity, species in the genus Creobroter have equally sensitive heari ng 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 origin ates from an auditory organ in the ventral midline of the metathorax t hat closely resembles the ear of other mantises. Ablation experiments demonstrate that low frequency sensitivity derives from a serially hom ologous 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 la tency, 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 ev idence suggests that they are two serially homologous sets of cells. N either auditory organ shows any physiological evidence of directional sensitivity. Ultrasound triggers a set of behaviors in flying hymenopo did mantises much like those in other mantises, but the behavioral sig nificance of low frequency hearing in these animals is still unknown.