Relationships among flight traits, genetic differentiation and habitats in two closely related species of the genus <i>Synuchus</i> (Coleoptera: Carabidae)

Abstract The degeneration of flight ability has contributed to the diversification of beetles, which are among the most diverse groups in the world. Over the course of flight ability degeneration, intraspecific polymorphisms in flight traits occur. The type of habitat in which degeneration of flight ability is likely to occur is an important issue for understanding the diversification process of beetles, but this topic has rarely been studied in detail. In this study, we examined two closely related species (one species with intraspecific polymorphisms in the hind wings and the other an apterous-monomorphic species) of the genus Synuchus to clarify this issue. Our study indicated that these two species were morphologically and genetically related, but they showed contrasting genetic differentiation patterns and inhabited different environmental conditions. In particular, the apterous-monomorphic species seemed to be isolated in mountainous environments with four major climatic and terrain characteristics (cool, heavy precipitation in winter, large temperature and precipitation differences, and low continuity among habitats), and this isolation might have contributed to their complete loss of flight ability and geographical genetic differentiation via further suppression of gene flows between populations.