Listening for males and bats: spectral processing in the hearing organ of Neoconocephalus bivocatus (Orthoptera: Tettigoniidae)
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Tettigoniids use hearing for mate finding and the avoidance of predators (mainly bats). Using intracellular recordings, we studied the response properties of auditory receptor cells of Neoconocephalus bivocatus to different sound frequencies, with a special focus on the frequency ranges representative of male calls and bat cries. We found several response properties that may represent adaptations for hearing in both contexts. Receptor cells with characteristic frequencies close to the dominant frequency of the communication signal were more broadly tuned, thus extending their range of high sensitivity. This increases the number of cells responding to the dominant frequency of the male call at low signal amplitudes, which should improve long distance call localization. Many cells tuned to audio frequencies had intermediate thresholds for ultrasound. As a consequence, a large number of receptors should be recruited at intermediate amplitudes of bat cries. This collective response of many receptors may function to emphasize predator information in the sensory system, and correlates with the amplitude range at which ultrasound elicits evasive behavior in tettigoniids. We compare our results with spectral processing in crickets, and discuss that both groups evolved different adaptations for the perceptual tasks of mate and predator detection.
KeywordsAcoustic communication Predator evasion Receptor tuning Hearing Ultrasound
We thank J.D. Triblehorn, O.M. Beckers, M. Talwar and R.L. Rodríguez for comments on the manuscript. This work was supported by grants from the University of Missouri Life Sciences Fellowship Program and grant Ho 3228/1-1 from the Deutsche Forschungsgemeinschaft to GH and the National Science Foundation to JS (NSF-IBN-0324290). Experiments comply with the “Principles of Animal Care” and with current laws in the USA.
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