RECOGNITION OF SEX IN THE ACOUSTIC COMMUNICATION OF THE GRASSHOPPER CHORTHIPPUS-BIGUTTULUS (ORTHOPTERA, ACRIDIDAE)

Many gomphocerine grasshoppers communicate acoustically: a male's call ing song is answered by a female which is approached phonotactically b y the male. Signals and recognition mechanisms were investigated in Ch orthippus biguttulus with regard to the cues which allow sex discrimin ation. (1) The stridulatory files on the hindfemur of both sexes are h omologous in that they are derived from the same row of bristles, but convergent with respect to the ''pegs''. In males the pegs are derived from the bristles, and in females from the wall of the bristle's cup. (2) Male and female songs are generated by similar, probably homologo us motor programs, but differ in the duration, intensity, ''gappyness' ' of syllables, risetime of pulses, and the frequency spectra. The hin dleg co-ordination during stridulation and the resulting temporal song patterns are less variable in males than in females. (3) For both sex es, recognition of a mate's signal depends on species-specific syllabl e structure. For males it is essential that the female syllables consi st of distinct short pulses, whereas females reject ''gappy'' syllable s. Males strongly prefer ''ramped'' pulses, females respond to syllabl es irrespective of steeply or slowly rising ramps. Males react only to the low-frequency component, whereas females prefer spectra containin g both, low and high frequency components.