Patterns of mating between two closely related ground crickets are not influenced by sympatry

Allonemobius fasciatus (De Geer) and A. socius (Scudder) (Orthoptera: Gryllidae) are small ground-dwelling crickets that meet and hybridize, to a limited extent, in a mosaic contact zone stretching from New Jersey to at least as far west as Illinois. To determine whether short-range signals such as visual cues, tactile stimulation, or pheromones are important in limiting gene flow between A. fasciatus and A. socius we carried out a study in the laboratory. A male or a female was placed in a cage with an A. fasciatus and A. socius individual of the opposite sex and the outcome, a conspecific or a heterospecific mating, was recorded. Overall, conspecific matings occurred more frequently than heterospecific matings. However, individuals from areas of sympatry were no more likely to mate with a conspecific than were individuals from areas of allopatry. Thus, the challenge posed by a related species has not resulted in a strengthening of positive assortative mating in these crickets.