JPN Press: Japan's diverse salamanders living proof of evolution
This is a Press Information page entitled JPN Press: Japan's diverse salamanders living proof of evolution within the Press / News Items section of Caudata.org --- &lt;u&gt;YOMIURI SHIMBUN&lt;/u&gt; &#40;Tokyo, Japan&#41; 04 September 06 Japan&#39;s diverse salamanders living proof of evolution &#40;Kevin Short&#41; The Galapagos Islands, off the western coast of South ...
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<u>YOMIURI SHIMBUN</u> (Tokyo, Japan) 04 September 06 Japan's diverse salamanders living proof of evolution (Kevin Short)
The Galapagos Islands, off the western coast of South America, are famous for their unique wildlife. When Charles Darwin visited the islands in 1835, he collected specimens of eight different species of finch. These birds, known collectively as "Darwin's finches," are all thought to be descendants of a single species that migrated to the islands from the mainland. Over a period of time, various populations of the original birds adapted to different local food sources and feeding methods by modifying the size and shape of their bill: long and sharp for snapping up insects and spiders; thick and massive for crushing heavy seeds; short and broad for cutting up green leaves; or heavy woodpecker-style bills for probing insects out of dead wood.
Darwin's finches are world famous as examples of how new species emerge. Lesser known, but equally valuable as evidence of speciation, are the many little Asian salamanders that live all over Japan. The finches of the Galapagos diversified by adopting different behavior, but the Japanese salamanders split up chiefly through the process of isolation.
Salamanders are widespread throughout the temperate zones of the Northern Hemisphere. Although they are sometimes confused with lizards, they are not reptiles at all, but amphibians with tails. Tailed amphibians, which also include newts and sirens, number fewer than 400 species worldwide, as opposed to nearly 4,000 species for their close cousins, the frogs and toads.
With their squat bodies and short legs, salamanders retain the basic form of their distant ancestors, the first vertebrates to crawl out of the sea and colonize the land some 360 million years ago. The Asian salamanders are thought to have originally evolved on the Asian mainland, and to have migrated into Japan during the glacial periods, when western Honshu and Kyushu were connected by land bridges to the Korean Peninsula.
These migrants from the continent found Japan much to their liking. As they spread across the country, they first split into two groups. One group stayed in the lowlands and river valleys, breeding in ponds, marshes and other bodies of still water. The other group worked their way up into the mountains, breeding in faster-flowing streams and creeks.
Japan is a small country broken up by range after range of steep mountains. As the salamanders spread eastward and northward, the populations in various valleys, as well as those living in various mountain ranges, became isolated from one another. Unable to interbreed, these populations drifted away from each other genetically, eventually evolving into separate species.
Asian salamanders found Japan so much to their liking that the number of species here now outnumbers that on the continent. In the genus Hynobius, for example, there are 28 species found worldwide, 16 of which live here in Japan. Furthermore, 15 of these 16 species are endemic, which means that they can be found only in this country.
The Hida salamander (Hynobius kimurae, or hida sansho-uo) is a typical Japanese mountain salamander, an endemic species inhabiting the mountains of central and western Honshu. The adults live in dense, moist forest that borders streams and ravines. During the day they stay hidden in the leaf litter, but at night, and during periods of rain and fog, they emerge to hunt for worms, slugs, spiders and ground-dwelling insects. Like all salamanders, this species is entirely carnivorous.
Come early spring, the Hida salamanders assemble in the nearby streams to mate. The females lay their eggs behind rocks or along the banks. The eggs are encased in tough gelatinous sacs, which are attached to the rocks to keep them from being swept away downstream.
The larvae hatch out in early summer. Frog tadpoles will eat algae and other plant matter, but salamander larvae are hunters right from the start, feeding on the larvae of mayflies and other aquatic insects. Like all of Japan's mountain salamanders, the Hida larvae are equipped with strong hooks on the tips of all their fingers and toes. These hooks help the young salamanders cling to rocks in the swift current, and are not found on the species that live in still waters.
The Hida salamander is short, stocky, and colored a dull bluish black or brownish black. Distinctive yellow spots on its back make this species relatively easy to identify. For the most part, however, Japan's species of Hynobius salamanders all look alike, and are very difficult to tell apart. To complicate matters, even individual species show a wide range of color patterns from region to region, and even among individuals.
One mountain salamander that can be easily identified is the Japanese clawed salamander (Hakone sansho-uo, or Onychodactylus japonicus). This species differs from the Hynobius species in being slimmer, with a tail that accounts for more than half its body length. The larvae take several years to turn into salamanders, and even after leaving the water require a few more years to reach sexual maturity.
Japan's biodiversity is exceptionally high in tailless amphibians, with 22 species as opposed to 37 species of frogs. Also, the large percentage of endemic species makes Japan a major factor in world salamander diversity. Unfortunately, salamanders require both excellent water habitat for their larvae, as well as contiguous moist forest habitat for the adults. As a result, 12 of the nation's tailless amphibians are now listed in the Environment Ministry's Red Data Book of Endangered Species.
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