Bioacoustics of Chorthippus (Chorthippus) karelini

Calling song. As a rule, a male of C. karelini produces 3–4, rarely up to 8 echemes separated by intervals of 1.5–2.5 s ( Fig. 3 A–C ). Each echeme lasts for about 0.3–0.5 s. In the echeme beginning, the male vibrates with the two legs synchronously; during the main part of a song, the legs move alternately, each leg at a rate of about 45–60/s. Oscillographic analysis shows that a first loud pulse and several subsequent quiet pulses are sometimes separated from the following 20–25 pulses of a song by a pause. However, this feature may vary individually. The sound pulses of the main part of each song follow at a rate of 90–120/s. The calling song of C. albomarginatus is very similar to that in C. karelini : the difference between these species lays mainly in the echeme duration (about 1.25 times more in C. albomarginatus than in C. karelini ) and pulse rate (about 1.25 times less in C. albomarginatus than in C. karelini ; Vedenina & Helversen, 2009 ). Such similarity in calling songs may prevent them from living together. On the other hand, the calling songs of the C. albomarginatus group substantially differ from the calling songs of C. angulatus and C. kegenicus ( Figs. 8 , 9 ). The calling echemes in both latter species last twice as long as in C. karelini . In C. angulatus , the two legs are moved much slower (22–40 /s) than in C. karelini , and the two legs are moved synchronously during the whole echeme. In C. kegenicus , the legs are moved at least three times slower than in C. angulatus , and this results to producing of 5–6 syllables per echeme. Courtship song. The courtship song of C. karelini starts with alternation of two elements, which are repeated with the period of about 1 s ( Fig. 3 D–F ). When producing an element 1, the legs vibrate synchronously at the rate of about 10–11/s. When producing an element 2, the two hind legs vibrate with a phase shift at the rate of about 26–32/s. Oscillographic analysis shows that the syllables of the element 1 consist of the well pronounced pulses repeated at the rate of 21–24/s, whereas the syllables of the element 2 contain much more dense pulses following almost without gaps. The alternations of these two elements can last up to 2–3 min, followed by a complex of three more elements. An element 3 is similar to the element 2, but is remarkably longer, reaching 4–8 s in duration. Then comes a rather short (200–400 ms), element 4, which is produced by the low-amplitude synchronous leg vibrations at the rate of about 40–53/s. A subsequent element 5 is accompanied by two fast strokes of the legs ( Fig. 3 F ). A second stroke is accompanied with lifting of abdomen and produced with the tibiae; the maximal angle between tibia and femur is 30°. Both strokes are produced with synchronous movements of the two legs, but most of the element 5 is generated by alternate leg movements. The element 5 reminds the calling song of C. karelini . The complex of the elements 3, 4 and 5 is usually repeated 2–3 times, and then again followed by the alternation of the elements 1 and 2. The courtship song of C. karelini strongly differs from the courtship songs of C. albomarginatus ( Vedenina & Helversen, 2009 ) , C. angulatus and C. kegenicus . In the two latter species, the courtship songs start with the small-amplitude movements of the hind legs, which generate short syllables repeated at the rate of about 3.5–6/s (element 1, Figs. 8 , 10 ). In about 0.2–1 min, there comes the elements 2 and 3; in contrast to the element 1, they are produced by rather complex leg movements. One of these elements remind the calling song of each species. However, the temporal structure of sound elements 2 and 3 is completely different from that in the C. karelini courtship, and the males of C. angulatus and C. kegenicus do not produce strokes with hind tibiae.

Morphology. The males of C. karelini can be reliably distinguished from those of C. albomarginatus , C. angulatus and the new species by the number of stridulatory pegs and the peg position and density on the proximal third of the stridulatory file ( Fig. 4 ). The peg number in C. karelini varies from 140 to 188 in different populations, being higher than in other three species (Table). On the proximal third of the file in C. karelini , the pegs are arranged in two or even three rows ( Fig. 4 A ), in contrast to other three species, in which the pegs are organized in one row. The males of C. karelini can be also distinguished from those of C. angulatus and C. kegenicus by the highest ratio of tegmen length to distance from the tegmen base to bifurcation of M vein (Table, Fig. 5 A ). The females of C. karelini can be distinguished from those of C. angulatus and C. kegenicus by the structure of stridulatory file. In C. karelini (and also in C. albomarginatus ), stridulatory pegs are thin and resemble the bristle stumps ( Fig. 6 A, B ). Moreover, proximal edges of the sclerotized walls surrounding these stumps are noticeably elongated. By contrast, the pegs in the C. angulatus and C. kegenicus females resemble the well-developed male pegs ( Fig. 6 C, D ). Both sexes of C. karelini tend to have the longest tegmina (Table, Fig. 7 A, B ) in comparison to C. angulatus and the new species.