- Scientists at Hiroshima University and Japan’s SOKENDAI, The Graduate University for Advanced Studies, found the tadpoles in shallow mud pools in the forests of the small, subtropical volcanic island of Kuchinoshima, which lies approximately 310 kilometers (192 miles) due South of Nagasaki, in the East China Sea.
- The researchers theorize that living in the hot springs, or onsen, may speed the tadpoles’ growth, benefit their immune systems, and allow them to survive on small volcanic islands where any other natural sources of freshwater are a rarity.
- No adult frogs were found in the onsen, suggesting that the species may be adapted to high water temperatures only as tadpoles.
Japan’s natural hot springs, or onsen, are frequented by locals and visitors alike, who relax in the year-round steaming water in public bathhouses. As it turns out, they’re not the only ones who enjoy the hot water: some tadpoles in Japan appear to be fans of the onsen as well.
According to a study published in the journal Amphibia-Reptilia, some Japanese tadpoles can live and grow in hot springs with water temperatures as high as 46.1 degrees Celsius (about 115 degrees Fahrenheit). The authors of the study theorize that living in onsen may speed the tadpoles’ growth, benefit their immune systems, and allow them to survive on small volcanic islands where any other natural sources of freshwater are a rarity.
Tadpoles of the same frogs, Japanese stream treefrogs (Buergeria japonica), have previously been found living in hot springs in Taiwan and on other Japanese islands. But the temperatures that the authors of the Amphibia-Reptilia study found the tadpoles living in are the hottest ever recorded for any amphibian tadpole.
The researchers — scientists at Hiroshima University and Japan’s SOKENDAI, The Graduate University for Advanced Studies — found the tadpoles in shallow mud pools in the forests of the small, subtropical volcanic island of Kuchinoshima, which lies approximately 310 kilometers (192 miles) due South of Nagasaki, in the East China Sea. No adult frogs were found in the onsen, suggesting that the species may be adapted to high water temperatures only as tadpoles.
Japanese stream tree frogs are the only species of amphibian native to Kuchinoshima and the rest of the islands in the Tokara Archipelago, a chain of volcanic islands off the Southwest coast of Japan. Adapting to life in water that is too warm for other amphibians probably allowed the species to exploit new habitats and avoid competition.
“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,” Takeshi Igawa of Hiroshima University, one of the study’s authors, said in a statement.
Igawa first noticed tadpoles in an onsen during a field trip in June 2013. He and his team returned to the same location in September 2015 in order to study them more closely. The scientists plan to focus future research efforts on the details of the tadpoles’ behavior in their hot springs habitat.
“Our goal is to understand the evolutionary processes that allow an animal to adapt to its environment,” Igawa said.
CITATION
- Komaki, S., Lau, Q., & Igawa, T. (2016). Living in a Japanese onsen: field observations and physiological measurements of hot spring amphibian tadpoles, Buergeria japonica. Amphibia-Reptilia. doi:10.1163/15685381-00003052