Parallel formation of hybrid swarms of ground beetles in the genus Carabus (Coleoptera: Carabidae) in adjacent river basins

Populations of forms intermediate between Carabus (Ohomopterus) insulicola and Carabus (Ohomopterus) arrowianus occur at the boundaries between the two species in the Kiso Valley, Nagano Prefecture, central Honshu, Japan. Morphological and mitochondrial DNA analyses revealed that these populations are derived from a hybrid swarm established as a result of secondary contact between the two species. A similar hybrid swarm has been reported in the Ina Valley, an adjacent river basin separated by the Kiso Mountain Range, where the two species are distributed parapatrically The hybrid swarm individuals in the two valleys show parallelism in the morphological evolution of the male genitalia upon secondary contact and subsequent formation of hybrid swarms between the two Carabus species.