High Degree of Mitochondrial Haplotype Diversity in the Japanease Common Toad Bufo japonicus in Urban Tokyo

Abstract

The Japanese common toad Bufo japonicus is widely distributed across mainland Japan and is classified into two subspecies, B. japonicus japonicus and B. japonicus formosus, in the western and eastern regions, respectively. To investigate the genetic diversity of B. japonicus at the breeding pond (local population) level, we sequenced 831 base pairs of mitochondrial DNA (mtDNA) cytochrome b (Cyt b) from 75 individuals collected from nine ponds in urban Tokyo and the surrounding area. Phylogenetic and population genetic analyses revealed high mtDNA haplotype diversity (Hd, 0.716 (mean) ± 0.230 (SD)) within local populations (breeding ponds). Most local populations had multiple haplotypes of the mitochondrial Cyt b gene, and seven of the 18 haplotypes were identified in two or more local populations. These results indicate that mitochondrial gene flow had occurred across different breeding sites. We also identified five haplotypes that belonged to the western clade and correspond to B. japonicus japonicus. Our results provide genetic evidence that B. japonicus japonicus was introduced artificially from Western Japan to Tokyo, where it occupied the natural habitat of B. japonicus formosus. The urban Tokyo area was found to represent an admixed population consisting of both native and non-native B. japonicus subspecies.