ACOUSTIC COMMUNICATION OF GRASSHOPPER MALES AFTER LESIONS IN THE THORACIC CONNECTIVES - CORRELATION WITH THE ASCENDING PROJECTIONS OF IDENTIFIED AUDITORY NEURONS

The most important aspects of the acoustic communication behaviour of grasshopper males are recognition and localization of a conspecific fe male's song. These capacities were investigated in Chorthippus biguttu lus males after various surgical operations on the connectives between meso- and metathoracic ganglia.Males with one connective transected c ompletely and a lateral incision on the second connective were still a ble to recognize the song and to decide to turn (though always to the semi-intact side). In contrast, a medial incision of similar depth, wh ile the second connective was transected completely, led to a complete loss of communication behaviour. Thus axons located in the lateral ha lf of the cross-section of the connective are not necessary for the pr ocessing of species-specific sound patterns, while axons in the medial half appear to be of major importance. These results are supported by a second experiment, in which a lesion was applied either to the medi al or to the lateral part of one connective, while the second connecti ve was left intact. Males with a lateral incision behaved normally, wh ile those with a medial incision showed turns to the wrong side. These results are compared with the positions within the connective of axon s of identified auditory interneurons. These axons are not evenly dist ributed over the cross-section of the connective, but are concentrated in three clusters. The most prominent group is located in the medial part of the connective. There is a good match between the location of this medial group of axons of auditory interneurons and the results of the lesion experiments.