THE AUDITORY-VIBRATORY SENSORY SYSTEM OF POLYSARCUS-DENTICAUDA (PHANEROPTERINAE, TETTIGONIIDAE) .3. PHYSIOLOGY OF THE VENTRAL CORD NEURONS ASCENDING TO THE HEAD GANGLIA

In Polysarcus denticauda, a phaneropterine bushcricket with extremely thick uncovered tympana and an aberrant morphology of the cristae acus ticae of the complex tibial organs, the electrophysiology of the audit ory-vibratory ventral cord neurons ascending to the brain was investig ated. Although the receptor organs in this species have some extraordi nary response properties, the central auditory-vibratory neurons could be basically classified into the same functional types of S-, V-, and VS-neurons previously described for other bushcricket species. Howeve r, in some details the responses of most of the S-and VS-neurons are d ifferent. The S-neurons are generally more tonic and the VS-neurons gi ve smaller responses to airborne sound stimulation than do the neurons belonging to the same functional types in most other bushcricket spec ies. Adult males of P. denticauda use an extremely complicated and var iable proclamation song for intraspecific acoustic communication. The song, which is often broadcast for a long time, can be divided into th ree phases on the basis of its time-amplitude structure. The syllable sequence exhibits some constant and other highly variable parameters. The basic, repeated element of the proclamation song is a pair of syll ables; both syllables in the pair differ in duration and amplitude as well as in repetition rate between the three phases. When P. denticaud a was stimulated with the conspecific male song, the responses of most S-neurons were found to copy the time patterns relatively well. Some of the V-and VS-neurons also responded relatively well to the syllable s when vibrational signals were presented simultaneously. However, und er these conditions the time structure was not copied, as it was by th e S-neurons. In comparative investigations, the responses of central n eurons of Decticus albifrons and Tettigonia viridissima, two species w ith more simply constructed songs having either low or high repetition rates, reflect the parameters of the song of P. denticauda less well than do the central neurons of P. denticauda. Therefore, some physiolo gical adaptations to this complex male proclamation song seem to be in herent in the reactions of these central neurons in P. denticauda. (C) 1997 Wiley-Liss, Inc.