Phylogeography of the Miyako Toad, Bufo gargarizans miyakonis (Anura: Bufonidae), Inferred from Mitochondrial Sequence Data

The Miyako toad, Bufo gargarizans miyakonis, is a subspecies endemic to the Miyako Islands of the Ryukyu Archipelago. The distribution of B. g. miyakonis is curious since no toads are found on other islands in the remaining part of the Ryukyu Archipelago. In this study, we conducted phylogenetic estimation and population genetic analyses using sequence data of the mitochondrial control region to clarify the phylogenetic position of B. g. miyakonis in the B. gargarizans species group and its population history. Results of phylogenetic analyses suggested that B. g. miyakonis was closely related to eastern populations of B. gargarizans and that there is incomplete lineage sorting among these populations. The divergence time between B. g. miyakonis and its closest lineages was estimated to be 0.54–0.75 Ma, the Middle Pleistocene, which was a little younger than the estimated value provided by the previous study. It is probable that the migration of the ancestor of B. g. miyakonis was strongly affected by the Middle Pleistocene glacial cycle. Population genetics analyses suggested that this subspecies experienced a rapid population size expansion, and that there is moderate genetic differentiation of sub-populations. Although the B. g. miyakonis population has a relatively high-level genetic diversity, it is also unique, having a significant number of accumulated mutations following rapid demographic expansion.