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Song discrimination by male cicadas Cicada barbara lusitanica (Homoptera, Cicadidae)

P. J. Fonseca^* and M. A. Revez

Departamento de Zoologia e Antropologia and Centro de Biologia Ambiental, Faculdade de Ciências de Lisboa, Bloco C2, Campo Grande, 1749-016 Lisboa, Portugal

View larger version (11K): [in a new window]   Fig. 1. Experimental arrangement. Only one half (180°) of the cage is represented. At the centre of the arena base, a small hole (5 cm in diameter) allowed a 60 cm long and 1 cm thick wood stick to project from a platform situated 15 cm below the base of the cage. The stimuli were presented by a loudspeaker positioned 60 cm away from the centre of the arena and 90 cm from the ground.

View larger version (21K): [in a new window]   Fig. 2. (A) Time taken by Cicada barbara males to respond to the songs of four sympatric cicadas presented at 70 and 90 dB. Values are means ± 95 % confidence intervals (N=8). (B) Oscillograms and power spectra of the songs of Cicada barbara, Tibicina quadrisignata, Tettigetta argentata and Cicada orni.

View larger version (21K): [in a new window]   Fig. 3. Effects of manipulation of the gross temporal pattern on song discrimination. Time taken by Cicada barbara males to respond to unmanipulated and manipulated songs of C. barbara and C. orni. Oscillograms are presented below the histogram. When pauses were inserted into C. barbara song the stimulus became unattractive and males could not discriminate it from the song of C. orni. Removing the pauses within C. orni song resulted in a very attractive stimulus, indicating that males are not able to discriminate between these species using only the differences in the frequency spectra. Values are means ± 95% confidence intervals (N=5).

View larger version (26K): [in a new window]   Fig. 4. The effect of varying pulse and pause duration on signal discrimination. The pulses for all stimuli were obtained from C. barbara calling song. (A) The pause duration was kept constant at 30 ms while the pulse duration was varied from 30 to 240 ms. All stimuli were equally effective (N=8). (B) The pause duration was varied between 7.5 and 120 ms while the pulse duration was fixed at 60 ms. Stimulus efficiency (measured as response latency to stimulus) decreased significantly with increasing pause duration. Values are means ± 95 % confidence intervals (N=5). DC, duty cycle (pulse duration/pulse period); NS, not significant.

View larger version (12K): [in a new window]   Fig. 5. Frequency discrimination by Cicada barbara males. Each male was stimulated with six sinusoidal tones at 80 dB SPL and the time taken by males to respond was measured. The conspecific song at the same sound intensity was presented for comparison. The 6 and 9 kHz tones were the most attractive. Singing behaviour was frequently not induced with 3 and 15 kHz tones within 180 s. Values are means ± 95 % confidence intervals (N=14).

View larger version (20K): [in a new window]   Fig. 6. Frequency-dependent auditory nerve suprathreshold response, estimated by the summed excitation of the auditory receptors. Values are means (N=7). Error bars represent 95 % confidence intervals. Variability at 70 and 90 dB SPL was similar to that shown at 80 dB SPL.