Abstract
BackgroundAuditory mate or prey localisation is central to the lifestyle of many animals and requires precise directional hearing. However, when the incident angle of sound approaches 0° azimuth, interaural time and intensity differences gradually vanish. This poses a demanding challenge to animals especially when interaural distances are small. To cope with these limitations imposed by the laws of acoustics, crickets employ a frequency tuned peripheral hearing system. Although this enhances auditory directionality the actual precision of directional hearing and phonotactic steering has never been studied in the behaviourally important frontal range.Principal FindingsHere we analysed the directionality of phonotaxis in female crickets (Gryllus bimaculatus) walking on an open-loop trackball system by measuring their steering accuracy towards male calling song presented at frontal angles of incidence. Within the range of ±30°, females reliably discriminated the side of acoustic stimulation, even when the sound source deviated by only 1° from the animal's length axis. Moreover, for angles of sound incidence between 1° and 6° the females precisely walked towards the sound source. Measuring the tympanic membrane oscillations of the front leg ears with a laser vibrometer revealed between 0° and 30° a linear increasing function of interaural amplitude differences with a slope of 0.4 dB/°. Auditory nerve recordings closely reflected these bilateral differences in afferent response latency and intensity that provide the physiological basis for precise auditory steering.ConclusionsOur experiments demonstrate that an insect hearing system based on a frequency-tuned pressure difference receiver achieves directional hyperacuity which easily rivals best directional hearing in mammals and birds. Moreover, this directional accuracy of the cricket's hearing system is reflected in the animal's phonotactic motor response.
Highlights
For many animals directional hearing is fundamental to their lifestyle as it forms the basis for prey detection, predator avoidance or mate localisation [1]
Our experiments demonstrate that an insect hearing system based on a frequency-tuned pressure difference receiver achieves directional hyperacuity which rivals best directional hearing in mammals and birds
Whereas vertebrate auditory systems generally rely on binaural sound level and arrival-time differences for the processing of directional information [2] these biophysical cues become tiny in animals like insects [3]
Summary
For many animals directional hearing is fundamental to their lifestyle as it forms the basis for prey detection, predator avoidance or mate localisation [1]. Specific adaptations are in place in some groups of insects [5,6,7] Despite their small size, directional hearing is present to different degrees in flies, crickets, and bush-crickets [8,9,3]. When the incident angle of sound approaches 0u azimuth, interaural time and intensity differences gradually vanish This poses a demanding challenge to animals especially when interaural distances are small. To cope with these limitations imposed by the laws of acoustics, crickets employ a frequency tuned peripheral hearing system. This enhances auditory directionality the actual precision of directional hearing and phonotactic steering has never been studied in the behaviourally important frontal range
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