Genetic population structure of Japanese bagrid catfishes

Abstract

The genetic population structures of four bagrid catfishes, allopatrically distributed in Japan, were investigated based on nucleotide sequence data from the mitochondrial control region (ca. 420 bp) of 296 specimens from 29 river systems. Almost no sequence variations were found within riverine populations of each species, especially Pseudobagrus ichikawai, in which no individual variations were found in any specimens from eight river systems throughout its range. In contrast, the P. nudiceps population in the Lake Biwa–Yodo River system showed relatively high polymorphism. These results imply that the riverine populations have undergone a bottleneck situation at some time. Most of the riverine populations of P. nudiceps and P. ichikawai, which are mainly distributed in areas around an inland sea or bay, were fixed into a single haplotype for each species. On the other hand, in P. tokiensis and P. aurantiacus, which are distributed in areas surrounding extensive mountainous regions, the haplotype compositions clearly differed among conspecific populations. These results suggest that some degree of gene flow existed among populations of each of the former two species during glacial regression periods. Based on the genetic variability of P. fulvidraco, widely distributed in continental East Asia, and the degree of genetic divergence between P. aurantiacus and its possible sister species, P. taeniatus, in China, the evolutionary rate of East Asian bagrids appears to be relatively low, estimated at a few percent per million years or less.