Phylogeography and genetic population structure of the endangered bitterling Acheilognathus tabira tabira Jordan & Thompson, 1914 (Cyprinidae) in western Honshu, Japan, inferred from mitochondrial DNA sequences

We examined the genetic population structure of the endangered freshwater cyprinid Acheilognathus tabira tabira in the Japanese archipelago, which has only been analyzed in limited sampling in previous studies, based on cytochrome b region of the mitochondrial gene. We confirmed the existence of the same three lineages determined in the previous study, the natural distribution area of Lineage I and II+III were considered to be the Seto Inland Sea and Ise Bay regions, respectively. Furthermore, the Seto Inland Sea region population was divided into five groups inhabiting neighboring water systems using the spatial analysis of molecular variance (SAMOVA). We estimated that populations in the Seto Inland Sea region migrated through a single paleowater system during the last glacial period and were then separated and genetically differentiated due to marine transgression. The Yoshino River system population was estimated to be a non-native population because it belonged to the same group as the Lake Biwa-Yodo River system, which is the only separate water system across the Seto Inland Sea. This study provides new evidence of genetic differentiation in A. t. tabira populations within the Seto Inland Sea region, where genetic differentiation has not been detected in previous studies, corresponding to five different groups by significantly increasing the number of individuals and sites compared with previous studies. Therefore, we propose these five groups as conservation units in the Seto Inland Sea region.