Distribution and Genetic Diversity of the Amphibian Chytrid in Japan.

While research on frog chytrid fungus , an infectious disease that threatens amphibian diversity, continues to advance worldwide, little progress has been made in Japan since around 2010. The reason for this is, which we pointed out in 2009, that the origin of frog chytrid fungus may be in the East Asian region, including Japan based on the ITS-DNA variation, and as few cases of mass mortality caused by this fungus have been observed in wild amphibian populations in Japan, the interest of the Japanese government and the general public in has waned. However, we believe that organizing the data obtained so far in Japan and distributing the status of frog chytrid fungus in Japan to the world will provide useful insight for future risk management of this pathogen. We collected more than 5500 swab samples from wild amphibians throughout Japan from 2009 to 2010. Then, we investigated the infection status using the Nested-PCR method. We sequenced the obtained DNA samples and constructed a maximum-parsimony (MP) tree to clarify the phylogenetic diversity of . We detected infection in 11 (nine native and two alien) amphibian species in Japan and obtained 44 haplotypes of ITS-DNA. The MP tree showed a high diversity of strains in Japan, that some strains belong to -GPL and -Brazil. Except for local populations of the Japanese giant salamanders in Honshu Island and the sword tail newts in Okinawa Island, the infection prevalence in native amphibian species was very low. The alien bullfrog had high infection rates in all areas where they were sampled. No infection was detected in other native amphibians in the areas where giant salamanders, sword tail newts, and bullfrogs were collected, suggesting that many native amphibians are resistant to infection. The sword tail newt of Okinawa Island had both the highest infectious incidence and greatest number of haplotypes. The giant salamanders also showed relatively high infection prevalence, but the infected strains were limited to those specific to this species. These two Caudata species are endemic to a limited area of Japan, and it was thought that they may have been refugia for , which had been distributed in Japan Islands for a long time.