Eurycorypha varia, Brunner von Wattenwyl, 1891

Heller, Klaus-Gerhard & Hemp, Claudia, 2020, Hyperdiverse songs, duetting, and the roles of intra- and intersexual selection in the acoustic communication of the genus Eurycorypha (Orthoptera: Tettigonioidea, Phaneropterinae), Organisms Diversity & Evolution (New York, N. Y.) 20 (4), pp. 597-617 : 611

Eurycorypha varia ( Figs. 3 , 4b , 6 , and 12)

The acoustic communication of E. varia was described by Hemp et al. (2013) from the songs of one couple. The new data presented here confirm the pattern. One male song unit ( Fig. 4b ) contains combinations of a soft and a loud part, which are called echemes, because they are most likely produced by two stridulatory movements (= two syllables; see Hemp et al. 2013, Figs. 4 and 5 ). Several (6.4 ± 1.5; range, 5–13; n = 5 males with 10 measurements each) of these echemes followed each other in rapid succession (echeme period, 554 ± 50 ms; second last syllable duration, 220 ± 33 ms), the first ones being shorter and softer than the last ones. At the beginning of such a sequence, the louder syllables were regularly followed by some loud and isolated impulses. The position of these isolated impulses was very similar to that of a female response. The male produced often several (rarely up to 18) of these song units at intervals of about 10 s, these calling bouts separated by many minutes of silence.

The females responded after the end of the second (loud and last) syllable of a male echeme ( Fig. 6 ). These responses often contained several loud and many soft impulses. Measuring from the end of the male syllable to the loudest female impulse, the mean of the female latency varied between 3 and 70 ms (3 females). The extremely short times resulted from the fact that in some females the response occurred occasionally before the end of the male syllable, producing negative delays. For example, the female from the Nguru Mountains answered to two different males with latencies of 3 ± 47 ms (n = 15; range, − 90 to 60 ms) and 8 ± 29 ms (n = 15; range, − 54 to 50 ms). Obviously, the end of the male syllable is not the correct trigger point, but due to the variability of the female and the varying soft parts of the male signal, no clear trigger point could be identified. Assuming the loudest point of the male syllable as trigger did not improve the results. Interestingly, sometimes female responses were recorded very late, at a time interval of about the duration of one echeme, after the male song had ended ( Fig. 6 ).

Surprisingly, one male regularly produced another type of song in addition, here called rivalry song. Placing two males and one female together and recording them for 2 h (two 2- channel recordings in two nights, recordings A and B), one male always produced the typical calling song and the female responded (recording A). The other male started also with the typical song, but after a few minutes switched to rivalry song. It produced it after echemes of the leading male’ s song or after responses of the female (recording B; Fig. 12 ; the song of the leading male can only be seen in the sonogram). If there was a female response, the rivalry song started after its beginning (92 ± 10 ms; n = 10) and consisted of series of 11.7 ± 5.4 loud impulses (range, 8–21) with a repetition rate of 28 Hz (period, 36.3 ± 2.5 ms). Between the loud impulses, regularly some soft ones were recognizable.

Figures

Fig. 3 Power spectra of male calling song of Eurycorypha species. In species with restricted frequency range, short black lines mark its end. Blue lines indicate power spectra of female responses

Fig. 4 a, b Oscillograms of male calling songs, overview (10 s sections)

Fig. 6 Oscillograms of male- female duets, overview (10 s sections)

Fig. 5 Oscillograms of male calling songs, details (1.5 s sections)

Fig. 12 Rivalry song and female responses of Eurycorypha varia. In the sonogram, the echemes of the leading male are marked with blue arrows (too weak to be seen in the oscillogram)