Conservation Genetics of the Endangered Sado Wrinkled Frog Glandirana Susurra Reveals Strong Regional Endemism and Population Bottlenecks

The Sado wrinkled frog (Glandirana susurra) is a recently described threatened amphibian species found only on Sado Island, a small island located off the north coast of Honshu, Japan. We conducted an extensive field survey and genetic analysis of G. susurra to identify its (1) large-scale distribution patterns, (2) remaining levels of genetic diversity, (3) major genetic groups (i.e., regional populations), and (4) levels of genetic differentiation and gene flow within and between its populations on the island. G. susurra was most prevalent in the central part of the island but was also observed in some areas to the east and west. We found a strong, hierarchical genetic structure that includes three genetically distinct groups of populations (‘eastern’, ‘central’ and ‘western’). The eastern and western regional populations had significantly lower genetic diversity than the central population. We found, however, that many local populations in the central population had experienced several recent bottleneck events. Conservation recommendations for G. susurra include (1) considering the three major groups of G. susurra populations as separate units for purposes of conservation planning, (2) increasing the population sizes of the eastern and western populations which showed relatively lower genetic diversity, and (3) increasing habitat connectivity to facilitate gene flow among local populations in the central part of the island.