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Evolutionary History of the Extinct Otter Lived in Japanese Islands

Daisuke Waku and Takeshi Sasaki

Although the river otter (Lutrinae) of Japan was distributed in four main Japanese islands until the 1920s, this animal has not been observed in the wild since 1979. Additionally, the taxonomic status of this otter remains controversial. Previous morphological and molecular genetics studies have suggested that the Japanese otter from the Honshu and Shikoku islands is an independent species of the genus Lutra, namely, Lutra nippon. However, there are pros and cons about this classification. In a recent study, our group determined the mitochondrial genome sequence of the two Japanese otter museum specimens, using next-generation sequencing technology, and evaluated the phylogenetic status of these specimens in the clade of Lutrinae. We suggested that the Japanese otter is of the genus Lutra and that two genetically divergent lineages exist among the Japanese otters living on Honshu and Shikoku. One of the lineages, which diverged from the ancestor of L. lutra at 1.27 million years ago, it should be treated either as the independent species L. nippon or as an independent subspecies of the Eurasian otter Lutra lutra nippon. The other lineage, which diverged from the ancestor of the Chinese population of L. lutra at 0.10 million years ago, was identified as L. lutra. However, in our previous study, we had analyzed genetic material from only one individual in each lineage. Therefore, our results cannot conclusively illustrate the natural history of the Japanese otter. Hence, future studies should use more than one individual to evaluate the genetic divergence of population of the Japanese otter.