抄録
We determined the nucleotide sequences of the non-coding region between the genes for tRNAThr and tRNAPro in 433 specimens of the deep-sea demersal fish Bothrocara hollandi obtained from the Japan Sea and the Okhotsk Sea. This region consisted of 1–3 copies of sequences, which originated from the duplication of the 5′-region of the tRNAPro gene. All the individuals from the Okhotsk Sea have two copies and those from the Japan Sea were shown to have 1–3 copies. Of the individuals obtained from the Japan Sea, those with more than one copy and those with a single copy corresponded to Group A and Group B, respectively, which have been defined in a previous study. On the other hand, a closely related species, Bothrocara tanakae, has a single copy, and no non-coding region was detected for the congeneric species Bothrocara molle. Duplication of the unit might have occurred three times during the evolution of B. hollandi. During the last glacial maximum (LGM) when most of the Japan Sea was anoxic, ancestors of Group A would have inhabited the shallower areas of the Japan Sea which did not become anoxic while those of Group B might have survived in other refuges in the Japan Sea. Low genetic diversity of Group B suggests that a severe bottleneck might have occurred in the population size of an ancestral population of Group B during the LGM.
