Origin and Diversification of Freshwater Fishes in Lake Biwa

Abstract

AbstractLake Biwa is the largest and oldest lake in Japan. It harbors more than a thousand animal and plant species, including 67 indigenous freshwater fish species/subspecies with 16 endemic or semi-endemic forms. Paleogeographical and paleontological studies have revealed that the location and environment of the lake have changed during its history of more than four million years. The current Lake Biwa, with its unique environments, was established 0.4 million years ago. Endemic fishes in Lake Biwa are traditionally divided into old “relict species” and new “species that evolved in the lake,” the latter being assumed to have evolved through ecological adaptations to the present lake environment. However, recent molecular phylogenetic/population genetic analyses have revealed that many of the “species that evolved in the lake” have origins that are older than the present Lake Biwa, while other species likely evolved in the present environment through ecological adaptation. On the other hand, many fish populations that inhabit Lake Biwa, irrespective of their origin, show similar patterns involving recent population expansions that occurred several tens of thousands of years ago. Extensive community level analyses of “lacustrine syndromes” that are found in Lake Biwa are necessary based on morphology, physiology, phylogenetics, population genetics, and also new “omics” approaches.KeywordsAdaptationAncient lakeDivergence timeEcological speciationEndemic speciesFossil recordsMitochondrial DNA (mtDNA)PhylogenyPhylogeography