Genetic variation and breeding program of Eurasian otters in Japanese zoos and aquariums

Eurasian otter (Lutra lutra) is a mid-sized species belonging to the order Carnivora and is distributed across a wide area of the Eurasian continent. This species comprises 11subspecies. The European subspecies (L. l. lutra), the Southeast Asian subspecies (L. l. barang), and the Chinese subspecies (L. l. chinensis) are reared in European and Japanese zoos and aquariums. Among these, the European facilities rear two lines, which were named A-line (L. l. lutra) and B-line (this is likely a crossbreed of L. l. lutra and L. l. barang); the Japanese facilities introduced these two lines. The mitochondrial (mt) DNA partial cytochrome b (cytb) sequence (307bp) of the A- and B-lines detected previously have shown slight but characteristic differences between the two lines. However, the previous study had limitations, as only one sample of the B-line was considered and the sequence was found to be short. Although, typically, breeding involves mating of individuals within the same subspecies, the A- and B-lines were crossbred in the Japanese facilities, which is likely because only small numbers of the Eurasian otter were reared in these facilities, thereby making cross-breeding imperative to the conservation of Eurasian otter in this country. In this study, we determined the complete cytb sequence (1140bp) from one individual each of the A- and B-lines, and two individuals of the Chinese subspecies. These sequences were compared and subjected to phylogenetic analysis, along with four individuals of Eurasian otter (which includes one B-line individual). The B-line individual showed diagnostic nucleotides at two positions, whereas the A-line individual showed diagnostic nucleotides at four positions. In the phylogenetic tree, two B-line individuals formed a monophyletic group with the two individuals of Chinese subspecies, and an A-line individual formed another monophyletic group with the other European individual. These results suggest that mtDNA sequence of B-line was derived from some Asian subspecies, and it differed from the A-line sequence (European subspecies). Moreover, because these results suggest that hybridization between the European subspecies and some Asian subspecies occurred in the B-line, the breeding program involving B-line individuals is not appropriate to the conservation of subspecies-specific strains.