A HYBRID ZONE BETWEEN 2 SUBSPECIES OF CHORTHIPPUS-PARALLELUS - X-CHROMOSOME VARIATION THROUGH A CONTACT ZONE

Two grasshopper subspecies, Chorthippus parallelus parallelus (Cpp) an d Chorthippus parallelus erythropus (Cpe), meet along the Pyrenees whe re they hybridize and produce a hybrid zone. A contact zone located in the Col de Portalet has been analyzed for the distribution of chromos ome markers on the sex (X) chromosome in pure and hybrid populations. C-banding allowed us to distinguish both pure subspecific forms and re combinant forms, and to demonstrate their different frequencies throug h the contact zone. Interestingly, the distal C-band (P) on the X chro mosome that characterizes Cpp individuals occurs at very high frequenc y through the zone and then drops sharply, close to where pure Cpe pop ulations are found. A novel interstitial C-band (H) has been found, pr obably derived from that characterizing Cpe individuals (E). This mark er band is only present in hybrid populations. These data are discusse d in the light of the dynamics of the hybrid zone.