Comparisons among morphological characters and between localities in the Chorthippus parallelus hybrid zone (Orthoptera: Acrididae)

Two subspecies of Chorthippus parallelus meet and hybridize in the Pyrenees. The hybrid zone between the two taxa is believed to have formed following range expansion at the end of the last glaciation and to be maintained by a balance between gene flow and selection against hybrids. The authors examined morphological characters in two cols about 200km apart. Clines are neither coincident nor concordant in either col, and are wider and more dispersed in the western col. The lack of concordance can be explained on several models for the maintenance of the hybrid zone. Lack of coincidence may be due to a difference in population structure between the cols: a patchy distribution of grasshoppers in the W col produces wider, more dispersed clines while a sharp break in distribution in the E col tends to concentrate morphological change over a shorter distance. -from Authors