Abstract
Caryopteris incana is a perennial shrub distributed in the temperate zone of the East Asia. It is found in West Kyushu in Japan, where it is designated as an endangered species. Tsushima, Nagasaki, which experienced repeated connection and fragmentation between the Korean Peninsula and Japan, is an island on the route along which C. incana moved to Japan from continental Asia. We conducted field work and confirmed the genetic structure of populations using DNA sequence analysis to construct a detailed distribution map and clarify the intraspecific phylogenetic relationships of C. incana in Tsushima Island. We confirmed 72 populations in Tsushima. Using the leaves of individuals cultivated from seeds collected from each natural population, we analyzed the chloroplast and nuclear DNA sequence variations. Among the populations, sequence variations were confirmed in six regions of chloroplast DNA, and six haplotypes, including base substitutions, were distinguished. Two haplotypes were mainly divided at the border of the northern part of the southern island in Tsushima. One population in the northwestern part of the north island showed a haplotype derived from the southern part. This finding revealed that the distribution of C. incana had been artificially influenced. Several haplotypes were confirmed by sequence variations in the northern populations, but only one haplotype in the southern populations, suggesting that C. incana on the north island had separated early from the south island in Tsushima.
Highlights
The distribution and variation of the existing organisms are the results of the accumulated effects of past population dynamics and evolutionary history
The field focuses, in particular, on genetic variation in phylogeography, and has been used to examine various species worldwide in order to clarify the evolutionary history of organisms that have survived the glacial and interglacial periods over the past tens of thousands to millions of years [2]-[5]
Some continental plant species have expanded their distribution to Kyushu and West Japan through Tsushima, and the intraspecific and interspecific genetic differences between the Japanese Islands, the Korean Peninsula, and Tsushima, which is a halfway point between the two, are important phylogeographical indices when considered along with the geological history and paleontology of these areas [10]
Summary
The distribution and variation of the existing organisms are the results of the accumulated effects of past population dynamics and evolutionary history. After the formation of each land bridge, many areas were geographically isolated by the subsequent rising sea level; for instance, many endemic species inhabit the Yakushima Island, which is famous for the Yaku cedar Among these regions, the islands of Tsushima, Nagasaki, have a mixed flora of species originating from the continent and from Japan as a result of the immigration and emigration of organisms with mainland Asia, because the Korean Peninsula and Tsushima were repeatedly connected and fragmentation by land [10]. Some continental plant species have expanded their distribution to Kyushu and West Japan through Tsushima, and the intraspecific and interspecific genetic differences between the Japanese Islands, the Korean Peninsula, and Tsushima, which is a halfway point between the two, are important phylogeographical indices when considered along with the geological history and paleontology of these areas [10]. Caryopteris incana (Thunb.) Miq. is one such species of continental plant
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