Urbanization causes habitat loss and fragmentation, which are suggesting major factors that strengthen local extinction and often disturb the genetic properties of populations by allowing hybridization with introduced species through human activities. In Japan mainland, there are two lineages of the Japanese common toads, the eastern Bufo japonicus formosus and the western B. j. japonicus, which diverged 5.7 Mya based on molecular data. Although the Tokyo area is originally the habitat range of B. j. formosus, the morphometric study suggested artificial introduction of B. j. japonicus. In this study, we analyzed the genetic structure of the B. japonicus group in urban Tokyo, using genetic markers: mitochondrial DNA CytB and seven loci of microsatellites. Our analysis revealed deep genetic introgression of invasive subspecies, B. j. japonicus, to the native one, B. j. formosus, in the Tokyo area. In addition, to estimate the influence of this genetic disturbance, we monitored and compared the survival rate of larvae in the urban (the Tokyo area) and the rural. Interestingly, the average of larval survivorship in the Tokyo area showed higher rates than rural ones.

Here, we provide a controversy if a human mediated introgressive hybridization could enhance the population persistence of the isolated urban toads.