Salinity and thermal tolerance of Japanese stream tree frog (Buergeria japonica) tadpoles from island populations

Physiological tolerance to variable environmental conditions is essential for species to disperse over habitat boundaries and sustain populations in new habitats. In particular, salinity and temperature are one of the major factors determining species' distributions. The tree frog Buergeria japonica is the most widely distributed amphibian species found in the Ryukyu Archipelago in Japan and Taiwan, and uses a wide range of breeding sites. Such characteristics suggest a high salinity and thermal tolerance in B. japonica tadpoles. We measured the salinity and thermal tolerance of tadpoles from three islands to determine if physiological tolerance could have contributed to the wide dispersal and survival across different environments. The critical salinity of B. japonica was 10–11‰, a value markedly below seawater. We also observed a critical maximum temperature of approximately 40°C, a value which is higher than what is commonly observed for other anuran species. This high thermal tolerance may have favoured island dispersal and survival, particularly in volcanic islands.