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THE CHRONICLE (San Francisco, California) 27 November 07 Rapid global warming threatens lungless salamanders (David Perlman)
Evolutionary biologists tracing the worldwide wanderings of a tribe of lungless salamanders have discovered that the tiny creatures survived through long periods of global warming millions of years ago, but the scientists doubt that salamanders now will make it in today's abruptly warming climate.
Like all amphibians - including frogs and toads - salamander populations are declining throughout the world, and many are threatened with extinction.
But two UC Berkeley scientists have found that what is fast becoming today's climate crisis for one family of salamanders may once have spurred their evolution and helped them diversify and extend their range widely from North America to Asia and Europe, and back again to what is now California.
David B. Wake, a widely known expert on the evolution of amphibians, and David R. Vieites, a postdoctoral researcher in Wake's lab and the Museum of Vertebrate Zoology, have combined the latest tools of genetics with well-tested theories of continental drift to develop a timetable for the ancient origins and travels of the four-legged animals.
A report by the Berkeley scientists and their colleague, Mi Sook Min of Seoul National University in Korea, is being published today in the online edition of the Proceedings of the National Academy of Sciences.
The lungless salamander family includes two-thirds of all the world's salamander species. They breathe through their moist skin instead of lungs as the other salamander families do.
Many scientists have long believed that the lungless family evolved some 300 million years ago in the Appalachian Mountains, but Wake and Vieites are proposing that the 2-inch-long creatures originated on both sides of North America about 100 million years ago when a vast sea spread across the center of the landmass and cool climates favored the amphibian's slow spread all across the continent's northern regions.
Here is part of the timetable laid out by the researchers:
About 70 million to 80 million years ago - during a period of global warming that may have lasted several million years - one warm-weather salamander tribe dispersed westward and north into Asia across what was then a land bridge linking the two continents where the Bering Sea now lies.
Then, about 40 million or 45 million years ago, during another long period of slowly warming climate, members of the same tribe of salamanders moved again - from Asia eastward into Europe, and also back again across the Bering land bridge into western North America.
Records of vegetation and fossil life during both periods show that climates then must have been much warmer than today's, the scientists agree, and the slowly warming climates favored the wide dispersal of the animals and their ability to adapt and diversify through evolution into the varied species that now exist.
To create their timetable - what geneticists now call a "biological clock" - the Berkeley biologists analyzed DNA from 43 different species of the lungless salamanders. Some was the type of genetic material called mitochondrial DNA that is carried only by females of all animal species, whether salamanders or humans. The other was nuclear DNA, which is found in the chromosomes of both males and females. By timing the mutation rates in both types of genes, the researchers created a rough biological clock to estimate the pace of the salamanders' biological changes.
"The salamanders were well able to adapt to the warming climate in those days, and it came on so slowly that it gave them an opportunity to disperse widely throughout the north," Vieites said in an interview. "But now, with global warming so abrupt, they will not be able to adapt in time, and that is at least one reason for their population decline - they could well go extinct."
Wake and Vieites have studied salamanders of the genus Hydromantes that are now native throughout California and the Western Hemisphere, and whose related species are found in France, Italy and Sardinia. They also analyzed the genes of Karsenia koreana, the only known species of its genus that was discovered, to the astonishment of the scientists, only two years ago in Korea.
That find, Wake said at the time, was "the most exciting and unexpected discovery of my career," because until then no scientists had believed that any lungless salamanders, all of them known together as plethodontids, had ever reached Asia. The Korean discovery was, in fact, a main impetus for this new study on the worldwide evolution and dispersal of the creatures during ancient periods of changing climate.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/11/27/BA23TJ8R3.DTL
Evolutionary biologists tracing the worldwide wanderings of a tribe of lungless salamanders have discovered that the tiny creatures survived through long periods of global warming millions of years ago, but the scientists doubt that salamanders now will make it in today's abruptly warming climate.
Like all amphibians - including frogs and toads - salamander populations are declining throughout the world, and many are threatened with extinction.
But two UC Berkeley scientists have found that what is fast becoming today's climate crisis for one family of salamanders may once have spurred their evolution and helped them diversify and extend their range widely from North America to Asia and Europe, and back again to what is now California.
David B. Wake, a widely known expert on the evolution of amphibians, and David R. Vieites, a postdoctoral researcher in Wake's lab and the Museum of Vertebrate Zoology, have combined the latest tools of genetics with well-tested theories of continental drift to develop a timetable for the ancient origins and travels of the four-legged animals.
A report by the Berkeley scientists and their colleague, Mi Sook Min of Seoul National University in Korea, is being published today in the online edition of the Proceedings of the National Academy of Sciences.
The lungless salamander family includes two-thirds of all the world's salamander species. They breathe through their moist skin instead of lungs as the other salamander families do.
Many scientists have long believed that the lungless family evolved some 300 million years ago in the Appalachian Mountains, but Wake and Vieites are proposing that the 2-inch-long creatures originated on both sides of North America about 100 million years ago when a vast sea spread across the center of the landmass and cool climates favored the amphibian's slow spread all across the continent's northern regions.
Here is part of the timetable laid out by the researchers:
About 70 million to 80 million years ago - during a period of global warming that may have lasted several million years - one warm-weather salamander tribe dispersed westward and north into Asia across what was then a land bridge linking the two continents where the Bering Sea now lies.
Then, about 40 million or 45 million years ago, during another long period of slowly warming climate, members of the same tribe of salamanders moved again - from Asia eastward into Europe, and also back again across the Bering land bridge into western North America.
Records of vegetation and fossil life during both periods show that climates then must have been much warmer than today's, the scientists agree, and the slowly warming climates favored the wide dispersal of the animals and their ability to adapt and diversify through evolution into the varied species that now exist.
To create their timetable - what geneticists now call a "biological clock" - the Berkeley biologists analyzed DNA from 43 different species of the lungless salamanders. Some was the type of genetic material called mitochondrial DNA that is carried only by females of all animal species, whether salamanders or humans. The other was nuclear DNA, which is found in the chromosomes of both males and females. By timing the mutation rates in both types of genes, the researchers created a rough biological clock to estimate the pace of the salamanders' biological changes.
"The salamanders were well able to adapt to the warming climate in those days, and it came on so slowly that it gave them an opportunity to disperse widely throughout the north," Vieites said in an interview. "But now, with global warming so abrupt, they will not be able to adapt in time, and that is at least one reason for their population decline - they could well go extinct."
Wake and Vieites have studied salamanders of the genus Hydromantes that are now native throughout California and the Western Hemisphere, and whose related species are found in France, Italy and Sardinia. They also analyzed the genes of Karsenia koreana, the only known species of its genus that was discovered, to the astonishment of the scientists, only two years ago in Korea.
That find, Wake said at the time, was "the most exciting and unexpected discovery of my career," because until then no scientists had believed that any lungless salamanders, all of them known together as plethodontids, had ever reached Asia. The Korean discovery was, in fact, a main impetus for this new study on the worldwide evolution and dispersal of the creatures during ancient periods of changing climate.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/11/27/BA23TJ8R3.DTL
