Taxonomy and ecology of alien Corbicula species - I: Invasion and dispersal in Japan and the world

Invasive alien bivalve species of the genus Corbicula, originally from Asia, were first introduced into North America in the 1920s and have spread around the world, including South America and Europe. In the 1980s, these species also entered Japan. The worldwide expansion of Corbicula species has resulted in negative ecological and economic impacts. To raise public awareness about this issue, I have written two review papers addressing questions such as "What are the scientific names and origins of Corbicula species?", "How and why have they been successfully introduced into new habitats?", "Why have they expanded their distribution areas?", "How have they influenced native ecosystems and local economies?", and "What types of measures should we take against the Corbicula issues?" The present paper is the first review, and it describes the taxonomic problems of Corbicula species and summarizes the information currently available on phylogenetic systematics using morphological and molecular data, which indicate sources, dispersion pathways, and introduction and dispersion mechanisms. Recent results of the phylogenetic systematics can be summarized as follows: 1) species and lineages cannot be identified based solely on morphology; 2) alien Corbicula species are composed of a few freshwater lineages, characterized by hermaphroditic and androgenetic reproduction; 3) considering the very subtle differences in shell morphology and the low genetic distance between the Japanese native species C. leana and the invasive C. fluminea, C. leana is estimated to be closely related to C. fluminea or a lineage within C. fluminea. The origin, introduction routes, and dispersion pathways of alien Corbicula species are being partly revealed by analyzing habitat preference, morphology, karyotype, sperm morphology, mode of reproduction, and genetic mitochondrial and nuclear DNA markers.