title: Variation in complex mating signals in an "island" hybrid zone between Stenobothrus grasshopper species.
abstract: Two grasshopper species Stenobothrus rubicundus and S. clavatus were previously shown to meet in a narrow hybrid zone on Mount Tomaros in northern Greece. The species are remarkable for their complex courtship songs accompanied by conspicuous movements of antennae and wings. We analyzed variations in forewing morphology, antenna shape, and courtship song across the hybrid zone using a geographic information system, and we documented three contact zones on Mount Tomaros. All male traits and female wings show abrupt transitions across the contact zones, suggesting that these traits are driven by selection rather than by drift. Male clines in antennae are displaced toward S. clavatus, whereas all clines in wings are displaced toward S. rubicundus. We explain cline discordance as depending on sexual selection via female choice. The high covariance between wings and antennae found in the centers of all contact zones results from high levels of linkage disequilibria among the underlying loci, which in turn more likely results from assortative mating than from selection against hybrids. The covariance is found to be higher in clavatus-like than rubicundus-like populations, which implies asymmetric assortative mating in parental-like sites of the hybrid zone and a movement of the hybrid zone in favor of S. clavatus.
authors.affiliation: Department of Neurobiology Johann-Friedrich-Blumenbach-Institute Göttingen Germany; Present address: Division of Nephrology Department of Internal Medicine III Dresden University of Technology Dresden Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Sradnick
authors.affiliation: Department of Neurobiology Johann-Friedrich-Blumenbach-Institute Göttingen Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Klöpfel
authors.affiliation: Department of Neurobiology Johann-Friedrich-Blumenbach-Institute Göttingen Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Elsner
authors.affiliation: Institute for Information Transmission Problems Russian Academy of Sciences Bolshoy Karetny per. 19 Moscow 127051 Russia.
authors.forename: Varvara
authors.initials: V
authors.lastname: Vedenina
keywords: Courtship song; Stenobothrus; geometric morphometrics; hybrid zone; linkage disequilibrium; sexual selection