Speciation in wide-spread plant species common to Bonin and Ryukyu Isls.

在我们以前的研究中，已经报道了小笠原群岛的特有植物不仅在形态上而且在遗传组成上与其祖先移民有区别。在小笠原群岛还发现了许多分布广泛的植物种类，这些植物也是从其他大陆通过长距离扩散迁移而来的。由于它们在地理上与其祖先种群以及岛屿以外的其他后代种群隔离，它们之间没有发生基因流动。然而，由于它们的形态特征似乎与其他地区的同类植物没有太大的不同，这些植物被列入同一物种。因此，有一个问题，这样一个广泛分布的岛屿物种是否没有遗传分化，从他们的大陆同行或没有？我们分析了小笠原种群和日本大陆种群之间的遗传分化。在Piper kazura（菊科）中，平均遗传同一性计算为0.78，在Tracheospermum asiaticum（夹竹桃科）的情况下，计算为0.80。从这些数据判断，它们与大陆同类的遗传同一性可能高于小笠原特有种。这一结果表明，形态分化的程度反映了遗传分化的程度。

In our previous studies, it has been reported that the endemic plants of the Bonin Islands are differentiated from their ancestral immigrants not only morphologically but also in their genetic conposition. In the Bonin Isles, ther found also many plant species which have a wide distribution through outside of the islands.These plants had also migrated from other landmasses by long distance dispersal. As they have been geographically isolated from their ancestral population as well as from other desendent populations outside of the islands, no gene flow has occured between them. However, as their morphological characters do not seem so much different from their counterparts growing on other areas, these plants have been included in the same species. Consequently there is a question whether such a wide-spread island species has no genetic differentiation from their continental counterparts or not?We have analyzed genetic differentiation between the Bonin population and that of mainland Japan. In Piper kazura (Piperaceae), mean genetic identity was caluculated as 0.78, and in the case of Trachelospermum asiaticum (Apocynaceae) it was calculated as 0.80. Judging from these data, it is likely that they have higher genetic identity to their mainland counterparts than the cases of Bonin endemic species. This results mean that the degree of morphological differentiation reflects the degree of genetic divergence.