A ZONE OF OVERLAP AND HYBRIDIZATION BETWEEN TWO GROUND CRICKET SPECIES.

In this paper I describe a zone of overlap and hybridization between the ground crickets, Allonemobius fasciatus and A. socius (Orthoptera: Gryllidae). The former occurs in the northeastern United States, the latter is found in the southeastern United States. They meet in a contact zone of variable width that extends from the East Coast to at least Ohio. In the Allegheny Mountains, where appropriate habitats for a species adapted to a northern climate and a species adapted to a southern climate are patchily distributed and widely intermingled, the zone is broad-at least 200 km. Along the coastal plain of New Jersey, where appropriate habitats are not as widely intermingled, the zone is comparatively narrow (5-100 km). Levels of hybridization were assessed by analyzing electrophoretic data, using population genetic models and a character index approach. Both methods of data analysis agreed-where the zone is broader, levels of hybridization appear reduced. © 1986 The Society for the Study of Evolution.