Chiba Satoshi
Institute of Biology and Earth Science, Shizuoka University, 836 Oya, Shizuoka, 422-8520, Japan.
Evolution. 1999 Apr;53(2):460-471. doi: 10.1111/j.1558-5646.1999.tb03781.x.
An endemic land snail genus Mandarina of the oceanic Bonin (Ogasawara) Islands shows exceptionally rapid evolution not only of morphological and ecological traits, but of DNA sequence. A phylogenetic relationship based on mitochondrial DNA (mtDNA) sequences suggests that morphological differences equivalent to the differences between families were produced between Mandarina and its ancestor during the Pleistocene. The inferred phylogeny shows that species with similar morphologies and life habitats appeared repeatedly and independently in different lineages and islands at different times. Sequential adaptive radiations occurred in different islands of the Bonin Islands and species occupying arboreal, semiarboreal, and terrestrial habitat arose independently in each island. Because of a close relationship between shell morphology and life habitat, independent evolution of the same life habitat in different islands created species possesing the same shell morphology in different islands and lineages. This rapid evolution produced some incongruences between phylogenetic relationship and species taxonomy. Levels of sequence divergence of mtDNA among the species of Mandarina is extremely high. The maximum level of sequence divergence at 16S and 12S ribosomal RNA sequence within Mandarina are 18.7% and 17.7%, respectively, and this suggests that evolution of mtDNA of Mandarina is extremely rapid, more than 20 times faster than the standard rate in other animals. The present examination reveals that evolution of morphological and ecological traits occurs at extremely high rates in the time of adaptive radiation, especially in fragmented environments.
海洋性小笠原（小笠原）群岛的特有陆地蜗牛属Mandarina不仅在形态和生态特征方面，而且在DNA序列方面都表现出异常快速的进化。基于线粒体DNA（mtDNA）序列的系统发育关系表明，在更新世期间，Mandarina与其祖先之间产生了相当于科间差异的形态差异。推断的系统发育表明，具有相似形态和生活栖息地的物种在不同的谱系和岛屿中在不同时间反复且独立地出现。在小笠原群岛的不同岛屿中发生了连续的适应性辐射，占据树栖、半树栖和陆地栖息地的物种在每个岛屿中独立出现。由于壳形态与生活栖息地之间的密切关系，不同岛屿中相同生活栖息地的独立进化在不同岛屿和谱系中创造了具有相同壳形态的物种。这种快速进化在系统发育关系和物种分类之间产生了一些不一致。Mandarina物种之间mtDNA的序列分歧水平极高。Mandarina内16S和12S核糖体RNA序列的最大序列分歧水平分别为18.7%和17.7%，这表明Mandarina的mtDNA进化极其迅速，比其他动物的标准速率快20倍以上。目前的研究表明，在适应性辐射时期，尤其是在碎片化环境中，形态和生态特征的进化以极高的速率发生。
