Japanese tadpoles relax in hot springs

One type of juvenile frog can survive in hot onsen water

Date: July 26, 2016

Source: Hiroshima University

Japanese tadpoles can live and grow in natural hots springs, or onsen, with water temperatures as high as 46.1oC (115oF). Living in onsen may benefit the tadpoles' immune systems, speed their growth, and allow the tadpoles to survive on small volcanic islands where there are few other natural sources of fresh water.

Tadpoles of the same frogs were previously found living in hot springs in Taiwan and other Japanese islands, but this field study found tadpoles living in the hottest ever recorded temperatures for any amphibian tadpole. The research was completed by scientists at Hiroshima University with collaborators at SOKENDAI, The Graduate University for Advanced Studies.

Japan's onsen attract locals and visitors to relax in the hot water year round in bathhouses built to contain the water in public tubs. The onsen where researchers found the tadpoles were shallow mud pools in the forests of the small, subtropical island of Kuchinoshima, approximately 310 kilometers (192 miles) due South of Nagasaki in the East China Sea.

"Scientists have studied the distributions of organisms and their environmental adaptations since the era of Darwin and Wallace. Our report is one of the best examples of a direct connection between an animal's physical ability to tolerate diverse environmental conditions and the animal's success at colonizing diverse geographic areas," said Takeshi Igawa, Ph.D., Assistant Professor at Hiroshima University and last author of the current study.

The tadpoles are Japanese stream tree frogs, known to scientists as Buergeria japonica. Japanese stream tree frogs are the only native species of amphibian on the Tokara Archipelago, a chain of volcanic islands off the Southwest coast of Japan. The adaptation to survive in water too warm for other amphibians may have allowed these frogs to exploit new habitats and avoid competition from other species. Future research will focus on the details of the tadpoles' behavior in their habitat.

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