Abstract
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.
Highlights
The Japanese otter, one of the semi-aquatic carnivores that lived in the rivers of Japan, was widely distributed in Hokkaido, Honshu, Shikoku and Kyushu until the 1920s (Figure 1) [1]
In 1989, Imaizumi and Yoshiyuki [5] conducted a comparative morphological study, using 15 Japanese otter specimens (13 individuals from Honshu and Shikoku; 2, from Hokkaido). They concluded that the morphological characteristics of otters from Honshu and Shikoku clearly differed from the species L. lutra; these otters should be classified as a distinct species, namely, Lutra nippon
The phylogenetic tree showed that the Japanese otter diverged genetically from the clade of L. lutra and formed a distinct lineage in the clade of Lutra. The gene sequence they used in their study was only 224 bp long, and their analysis did not include the other two species of Asian otters, namely, the hairy-nosed otter Lutra sumatrana and the smooth-coated otter Lutrogale perspicillata. All these studies suggest that the Japanese otter from Honshu and Shikoku could be an independent species, L. nippon, because it diverged genetically and morphologically from L. lutra, and the book Mammal Species of the World introduced this classification for the Japanese otter [9]
Summary
The Japanese otter, one of the semi-aquatic carnivores that lived in the rivers of Japan, was widely distributed in Hokkaido, Honshu, Shikoku and Kyushu until the 1920s (Figure 1) [1]. In 1989, Imaizumi and Yoshiyuki [5] conducted a comparative morphological study, using 15 Japanese otter specimens (13 individuals from Honshu and Shikoku; 2, from Hokkaido) They concluded that the morphological characteristics of otters from Honshu and Shikoku clearly differed from the species L. lutra; these otters should be classified as a distinct species, namely, Lutra nippon. The gene sequence they used in their study was only 224 bp long, and their analysis did not include the other two species of Asian otters, namely, the hairy-nosed otter Lutra sumatrana and the smooth-coated otter Lutrogale perspicillata All these studies suggest that the Japanese otter from Honshu and Shikoku could be an independent species, L. nippon, because it diverged genetically and morphologically from L. lutra, and the book Mammal Species of the World introduced this classification for the Japanese otter [9].
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