A narrow hybrid zone between the grasshoppers Stenobothrus clavatus and S. rubicundus: female preferences for courtship songs
V. Vedenina (1), S. Faehsing (2), J. Sradnick (2), A. Kloepfel (2), N. Elsner (2)

1) Institute for Information Transmission Problems, Russian Academy of Sciences, Bolshoy Karetny per. 19, 127994 Moscow, Russia. E-mail: vedenin@iitp.ru
2) Department of Neurobiology, Johann-Friedrich-Blumenbach-Institute, Berliner Str. 28, D-37073 Göttingen, Germany

Two grasshopper species, Stenobothrus rubicundus and S. clavatus, were previously shown to hybridize in a narrow contact zone on Mount Tomaros in northern Greece. The species are characterized by complex and completely different courtship songs. In the current study, we investigated female preferences for the courtship songs of S. rubicundus, S. clavatus and hybrids in playback experiments. Playback of the courtship songs revealed assortative preferences in females of the parental species: they significantly more often preferred the songs of conspecific males. Hybrid females showed a lower selectivity than parental females, responding somewhat equally eager to playback of the songs of S. clavatus, S. rubicundus and natural hybrid song, but less actively to the F1 hybrid song. The results evidence that hybrid males may lose to males of parental species, whereas hybrid females would even have an advantage over parental females. Comparison of responses of females from allopatric populations and Mount Tomaros to different song types shows no evidence for reinforcement. Asymmetry found in female preferences may have implications for the structure of the hybrid zone.