Tsugaru Strait hybrid zone between two Japanese marine sculpins (genus Cottiusculus)

Mitochondrial and nuclear DNA variations in the marine sculpin sister species Cottiusculus schmidti and C. nihonkaiensis, distributed along the Pacific coast of northern Japan and in the Sea of Japan, respectively, indicated a ca. 250-km-wide hybrid zone across the Tsugaru Strait, connecting the Pacific Ocean and Sea of Japan. In addition to incomplete postzygotic isolation between the two species, the hybrid zone may have been shaped and formed by reduced dispersal, the preferred habitat of Cottiusculus being generally deeper than Tsugaru Strait (maximum depth ca. 140 m).