Complex courtship in a bimodal grasshopper hybrid zone

V.Yu. Vedenina (1) and O. von Helversen (2)

1)Institute for Information Transmission Problems, Russian Academy of Sciences, B. Karetnyi per. 19, Moscow 101447, Russia
2)Institut fur Zoologie II, Universitat Erlangen-Nurnberg, Staudtstrasse 5, D-91058 Erlangen, Germany

Grasshoppers of the Chorthippus albomarginatus-group, which is outstanding with respect to its complex courtship song, were studied at fifteen localities in the Ukraine and Moldova. The analysis of the courtship songs revealed two species: C. albomarginatus in the north-eastern Ukraine and C. oschei in the south-western Ukraine and in Moldova. In a belt about 200 km wide, not only were one or the other pure species found, but also males with intermediate song characters. C. albomarginatus and C. oschei were hybridised in the laboratory, and F1 hybrid males as well as F2 hybrid males produced intermediate song patterns, quite similar to those recorded in the field. We defined a “hybrid song score” for intermediate songs. The score showed a bimodal distribution with most songs resembling one or other parental type, but with only a few intermediates. At several localities, where hybrids with songs similar to one of the parental species dominated, some individual males sang more similarly to the other species. In one locality, two hybrid populations only 3 km apart had different parental types. Hybrid songs can contain novel elements, even more complex than the parental ones, which may offer a new starting point for sexual selection. We suggest that genetic introgression occurs between the two sibling species C. albomarginatus and C. oschei within a wide hybrid zone stretching over a distance of several hundred km, but with a patchy spatial distribution.