Gomphocerus sibiricus (Linnaeus, 1767)

Distribution. Scandinavia, northern half of European Russia, Siberia, northern part of the Russian Far East, steppes of Mongolia and northern China. Mountains of Western Europe, Asia Minor, the Caucasus, Central Asia and Tibet.

Material. 2. Kazakhstan, Akmola region, 90 km SW of Kokshetau, environs of Balkashino, meadows near the forest, 52°30,4’ N, 68°43,2’ E, 26.06.2018, song recordings in 4 ³.

References to song. Faber, 1953: verbal description only, calling and courtship songs; Elsner, 1974: recordings from Switzerland, courtship song; Ragge & Reynolds, 1998: recordings from France and Italy, calling and courtship songs; Bukhvalova & Vedenina, 1998: recordings from Russia (Chita region), calling song; Tishechkin & Bukhvalova, 2009b: recordings from Russia (Buryatia), calling song; Tishechkin, 2017: recordings from Russia (Irkutsk region) and Kyrgyzstan, calling song; Willemse et al., 2018: recordings from Greece, calling song.

Song. The courtship song of G. sibiricus starts as an echeme similar to the calling song but lasting longer, up to 2 min (element 1). The echeme begins quietly, reaching maximum intensity in about 6–12 s (Fig. 9 A, B). The echeme consists of syllables repeated at the rate of about 5-6/s. The hind legs are almost synchronously moved up and down, but the sound (6-7 pulses) is only produced during the down-stroke (Fig. 9 F). One leg is usually moved down gradually, whereas another leg is moved down in a stepwise manner. The frequency spectrum of the sound occupies a broad band up to 50 kHz with many maxima in the range of 5–30 kHz (Fig. 9 G). The element 1 is sometimes followed by a series of much quieter syllables (element 2 or ‘aftersong’) repeated at the rate similar to that in the main echeme (Fig. 9 A, C). The main echeme with ‘aftersong’ or without it may be repeated several times until a male would reach a high degree of excitation. Then, the male demonstrates a complex visual display. The anterior part of the body is raised, the palps are moved, and the clubbed antennae are swung in such a way as they describe a cone (Fig. 10). Simultaneously with the antennae movements, the legs produce 3–4 short pulses and one longer pulse (Fig. 9 E). This visual display may be repeated several times before the male attempts to copulate with a female.

The attempt to copulate in G. sibiricus is accompanied by boxing movements with the fore legs unusual for other gomphocerine grasshoppers (Fig. 11). The G. sibiricus males have conspicuously swollen fore tibiae. During climbing on the female, the male beats her with his fore tibiae, lifting them almost vertically and dropping them at the rate of about 20/s.

Comparative remarks. Our recordings of G. sibiricus from Kazakhstan do not differ from the recordings made by various authors from other regions. However, in G. sibiricus from Switzerland (Elsner, 1974) both legs always produce identical stridulatory pattern. By contrast, it often happens in the specimens from Kazakhstan that one leg is moved down gradually, whereas another leg is moved down in a stepwise manner.

Despite courtship behaviour of G. sibiricus has been previously described from Western Europe (Faber, 1953; Elsner, 1974; Ragge & Reynolds, 1998), there are no figures that illustrate the antennae movements. The characteristic boxing movements that precede mating are also not comprehensively discussed in the literature, despite the video recordings of these movements are available in Internet (e.g. https://www.youtube.com/watch? v=F3e3kSuD- _A). The swollen fore tibiae of G. sibiricus are a characteristic feature of this species used in various taxonomic keys, but the function of this feature is not usually discussed. It is very likely that the males box the females to stimulate them to mate. Thus, sexual selection is suggested to be the main driving force for evolving the swollen fore tibiae in G. sibiricus males.