Showing papers by "Roger K. Butlin published in 1991"
TL;DR: This article examined morphological characters in two cols about 200 km apart and compared the positions and widths of dines for these characters both within and between cols, finding that clines are neither coincident (centred in the same position), nor concordant (equal in width) in either col.
Abstract: Two subspecies of the grasshopper, 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. Laboratory FI hybrid males are sterile. We have examined morphological characters in two cols about 200 km apart and compared the positions and widths of dines for these characters both within and between cols. Clines are neither coincident (centred in the same position), nor concordant (equal in width) in either col. Furthermore clines 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 and is a common observation. There are many fewer examples of lack of coincidence and this result is more difficult to interpret. We suggest that it is due to a difference in population structure between the cols: a patchy distribution of grasshoppers in the western col produces wider, more dispersed dines while a sharp break in distribution in the eastern col tends to concentrate morphological change over a shorter distance.
58 citations
TL;DR: It is argued that either of the patterns applied to sixteen populations in a transect across a hybrid zone in the grasshopper implies that selection operates on female preferences in the hybrid zone.
Abstract: A method for studying variation in female preference among populations free from the confounding effects of variation in male characters is described. This method is applied to sixteen populations in a transect across a hybrid zone in the grasshopper, Chorthippus parallelus. Significant variation in preference is revealed among populations. The pattern of this variation is analysed in the context of the reinforcement model of speciation. While the data do indicate an increased homogamic preference on one side of the zone relative to more distant populations, this pattern cannot be distinguished statistically from an abrupt transition in preference over a distance of less than 1 km. We argue that either of these patterns implies that selection operates on female preferences in the hybrid zone.
53 citations