Evolution in frontier environments

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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.