COMPARISON OF SONG FREQUENCY AND RECEPTOR TUNING IN 2 CLOSELY-RELATEDBUSH-CRICKET SPECIES

The songs and the structure and physiology of the auditory organs in t he closely related bushcricket species Tettigonia viridissima and Tett igonia cantans were investigated comparatively using bioacoustical, hi stological and neurophysiological methods. The morphology of the crist a acustica, the main auditory receptor organ, is very similar in the t wo species in respect to both the distribution of scolopidia along the length axis of the crista and the dimensions of corresponding scolopi dia and attachment structures. The only obvious difference is that T. viridissima has one more scolopidium in the crista acustica and that t he overall length of the crista is by about 50 mu m larger than in T. cantans. In contrast, differences were found in the physiology of indi vidual auditory receptor cells. Comparison of the threshold characteri stics of all the receptor cells of the crista acustica in both species reveals a differential sensitivity of groups of auditory receptor cel ls at dominant frequencies of the sang. In each species, the sensitivi ty of auditory receptor cells is matched to the energy spectrum of the song. These differences in the physiology can partly be explained by differences in transmission characteristics of the acoustic trachea.