Population Structure of Upstream Fat Minnow (Rhynchocypris oxycephalus) Based on Mitochondrial DNA Cytochrome b Analysis in Japan

Abstract

Population genetic analysis using mtDNA sequence analysis was carried out to clarify the population structure of Rhynchocypris oxycephalus in Japan. For each of 499 individuals from 71 localities, 506 bp of an mtDNA sequence from the 3ʹ end of the cytochrome b region was obtained and 187 haplotypes were identified. The haplotypes were differentiated into two large groups: Group I and Group II. Group I was divided into two subgroups (Subgroups A and B) and Group II was divided into five subgroups (Subgroups C, D, E, F, and G). The mean of the genetic heterogeneity value (F_ST) between each subgroup was 0.755, and the mean of the sequence divergence between each group was 5.5%. These results indicate a high level of genetic diversity and geographic differentiation.

Subgroup A was distributed from Tottori Prefecture and west to Kyushu on the Sea of Japan side. Subgroup B was limited to some rivers on the Pacific Ocean side of Shikoku. Subgroup C was distributed along the inland sea of the Kii Channel to the eastern Seto Inland Sea, mainly in Tokushima, Wakayama, and Hyogo Prefectures. Subgroup D was distributed only in the Kuzuryu River. Subgroup E was distributed in the area around Ise Bay and in central and western Shizuoka Prefecture. Subgroup F was collected from one river in Toyama Prefecture and two rivers in Aichi Prefecture. Subgroup G was distributed in the Ado River and several other rivers, and the Yahagi River was also likely a natural distribution region. The results suggest a relationship between the time of divergence between each subgroup and past geograpic events in Japan. The individuals collected in four localities (Tama River, Niizaki River, and two rivers in Yamagata Prefecture) are genetically closely related to the haplotypes in Lake Biwa, suggesting those fish may be alien species from Lake Biwa.