| Summary: | Nucleotide sequences of a 1,854 base pair region of the nuclear small subunit(18S)rDNA gene and of a 475 or 476 base pair region of the mitochondrial large subunit(mt16S)rRNA gene were determined for Euphausia pacifica collected from the western/eastern subarctic Pacific,Okhotsk Sea and Japan Sea, and Thysanoessa inermis from the Okhotsk Sea T.inermis from the Okhotsk Sea and Bering Sea. Interspecific differences were 0.16-0.86% for 18S rDNA gene and 2.3-9.3%for 16S rRNA gene. Intraspefic differences are of special interest of E.pacifica from geographically distant sites,but were very small(0.0-<0.1%for 18S rDNA, and 0.0-0.4%for 16S rRNA). The lack of the regional haplotype structure in E.pacifica suggests significant gene flow mediated by the ocean-scale circulation system for those living in the west-east subarctic Pacific and Bering Sea. For the Japan Sea population which has been isolated from populations in the Subarctic Current originating 8,000 years ago,the time scale is considered to be not long enough to observe variations. On the basis of phylogenetic trees established,the position of the three euphausiids was briefly discussed.
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