Genetic Compatibility and Geographic Profile of Two Closely Related Species of Allonemobius (Gryllidae: Orthoptera)

Abstract

Genetic compatibility between two species of ground crickets, Allonemobius fasciatus De Geer and A. socius Scudder, was studied by crossing experiments. Reciprocal crosses produced viable offspring. However, the number of eggs produced by A. fasciatus (♀) × A. socius (♂) was significantly smaller than that by the reciprocal cross or intraspecihc crosses; the hatchability was <10%, whereas most eggs produced in the other crosses overwintered and hatched. In the laboratory, development time for the male hybrids produced by A. socius (♀) × A. fasciatus (♀) was similar to that of their mothers rather than fathers, but the hybrid females were intermediate between the parent species, suggesting that nymphal development is primarily controlled by the X chromosome. The two species and their hybrids showed different ranges of embryonic stages for water absorption and diapause. Crickets collected from different localities in eastern North America were identified to species by their different diapause stages. The results were consistent with others' observations that the two species meet at around 38—39° N where hybrids occur. The geographic profiles and the possible isolating mechanisms between the two species are discussed.