Evolution in frontier environments

以西北太平洋小笠原群岛特有的陆螺属Mandarina为材料，研究了其适应辐射的生态和遗传过程。基于栖息地分析，形态分析，和检查的线粒体DNA序列的变化，我们表明，杂交发生在同域物种之间的栖息地利用，由于环境的变化。这表明，物种形成和适应性辐射仍在进行中Mandarina。此外，在形态上密切相关的物种之间构成的杂交区中发现了具有独特壳形态的种群。这表明杂交是创造新形态和进化新奇的重要来源。根据线粒体DNA序列估计了日本大陆陆地蜗牛Euhadra种之间的系统发育关系。在更新世期间，与气候变化有关，在尤哈德拉发生了反复的扩张和移民。通过生态学、形态学和遗传学（线粒体DNA和核ITS基因）分析，探讨了三角帆蚌（Batillariacumingii）与其寄生虫的关系。遗传分析表明，这些寄生虫包括大量的神秘物种。这些物种在遗传变异上表现出较少的地理变异。另一方面，硅藻属的遗传组成表现出较高的地理变异水平。生境变化引起的生态物种形成是潮间带腹足类寄生虫多样性的主要原因。

Ecological and genetic process of adaptive radiation were examined using endemic land snail genus Mandarina of the oceanic Ogasawara Islands in the northwestern Pacific. Based on the habitat analysis, morphological analysis, and examination of the mitochondrial DNA sequence variations, we showed that hybridization between sympatric species occurred by alteration of habitat use due to environmental change. This suggests that speciation and adaptive radiation are still in progress in Mandarina. In addition, populations with unique shell morphologies were found in a hybrid zone constituted between morphologically closely related species. This suggests that hybridization is an important source of creating novel morphology and evolutionary novelty.Phylogenetic relationship among the species of the land snails Euhadra in the mainland of Japan was estimated on the basis of mitochondrial DNA sequences. Repeated expansion and immigration have occurred in Euhadra, associated with climatic change during the Pleistocene. Complex spatial structure in genetic variations was created by mixing and isolation that were accompanied with the climatic change.Relationship between intertidal gastropoda Batillaria cumingii and its parasites was examined on the basis of ecological, morphological and genetic (mitochondrial DNA and nuclear ITS gene) analysis. Genetic analysis revealed that these parasites include a large number of cryptic species. These species showed less geographical variations in genetic variations. On the other hands, Batillaria showed a high level of geographical variations in genetic components. Ecological speciation due to habitat shift would be a main cause of diversification of parasites in intertidal gastropoda.