The Transitional Zones Found between Areas Characterized by the Four Geographical Forms of the Brachypterous Grasshopper Parapodisma setouchiensis and their Historical Formation Processes(PROCEEDINGS, JSSZ SYMPOSIUM, 2006)

Abstract

Parapodisma setouchiensis (Orthoptera: Acridiae) is a polytypic species consisting of four geographic forms (the Basic, Yamato, Tanba, and Mt. Hyonosen forms) with its highest morphological diversity in the area composed of the Chugoku District and the western part of the Kinki District, western Honshu, Japan. Narrow transitional zones can be identified between the areas defined by these four forms, where individuals with various intermediate characters occur. These individuals might have originated from secondary contact with different forms from ca. 150,000 to 100,000 years ago to the recent. Many recent studies have revealed that the boundaries of regions containing remarkable geographic differentiations for several terrestrial animals are frequently found in these areas. The Paleo-Chugoku District might have been the "great blank area" for these terrestrial animals during the Last glacial age