Two Tasmanian Tigers in the Smithsonian’s National Zoo, Washington D.C., about 1906, by E.J. Keller, from the Smithsonian Institution.
All the genes that the Tasmanian Tiger, an extinct carnivorous marsupial, inherited only from its mother will be revealed by an international team of scientists in a research paper to be published today in the online edition of Genome Research.
“The research marks the first successful sequencing of genes from this carnivorous marsupial,” according to a news release by Penn State University.
“Tasmanian Tiger” is a common name of the extinct thylacine species (Thylacinus cynocephalus), which is more closely related to kangaroos and koalas than to tigers. The last known specimen died in a Tasmanian zoo in 1936.
Thylacines have played a central role in discussions about the possibility of bringing extinct species back to life, but despite the availability of many bones and other remains, previous attempts to read thylacine DNA had been unsuccessful.
But now Penn State researchers have cracked the problem, using new gene-sequencing technology and computational methods developed by Webb Miller, a professor of biology and of computer science and engineering, and Stephan C. Schuster, a professor of biochemistry and molecular biology.
Tasmanian Tiger (Thylacine) at the Hobart Zoo, from Australia National Archives
The new methods involved extracting DNA from the hair of extinct specimens, not from bone, which has been used in previous studies of extinct species.
The team’s work reveals that hair is a powerful time capsule for preserving DNA over long periods and under a wide range of conditions, the university release said.
“I think of hair as a shrine for ancient DNA,” Schuster said. “It is sealed so well that not even air or water are able to penetrate the DNA stored inside. Most importantly, bacteria cannot reach the DNA as long as the structure of the hair remains sound.”
The research also opens the door to the widespread, nondestructive use of museum specimens to learn why mammals become extinct and how extinctions might be prevented, the release added.
“Our goal is to learn how to prevent endangered species from going extinct,” Webb said. “I want to learn as much as I can about why large mammals become extinct because all my friends are large mammals,” Miller said. “However, I am expecting that publication of this paper also will reinvigorate discussions about possibly bringing the extinct Tasmanian Tiger back to life.”
Miller, Schuster, and their colleagues were the first to report the genome-wide sequence of an extinct animal, the woolly mammoth, in November 2008. (Read the National Geographic News story about this.)
They next collaborated with Anders Goetherstroem, at Uppsala University in Sweden, to target the Tasmanian Tiger because, like the mammoth, it was a coveted goal of ancient-DNA researchers, who considered its sequencing unfeasable due to the inadequate quality of the DNA available from specimens, the Penn State release said.
“The speculation was that the only reason we were able to extract DNA from mammoth hair is that the mammoths had remained frozen in the Arctic permafrost, but our success with the Tasmanian Tiger shows that hair can protect DNA for long periods under a variety of environmental conditions,” Schuster said.
In their new paper in Genome Research, Miller, Schuster, and their colleagues describe the completion of the mitochondrial genome sequences of two Tasmanian Tigers, one at the Smithsonian Institution and the other at the Swedish Museum of Natural History.
One specimen was prepared by a taxidermist as a skin and the other one was submerged in ethanol. The team extracted DNA from small amounts of the hair of both specimens.
The gene sequences permitted the team to accurately determine how the Tasmanian Tiger is related to other marsupials. They also discovered that the two thylacine sequences were extremely similar to each other, suggesting that, as the species neared extinction, there was too little genetic diversity to resist bacterial and other environmental stresses.
“Low genetic diversity is appearing as a common theme in the extinct species being studied by our team,” Schuster said.
The new study shows that the methods pioneered at Penn State are potentially useful for a new discipline involving the genome analysis of samples originating from museum archives, which Schuster calls “Museomics.”
“The collections dating back several hundred years and now housed in the world’s museums of natural history are the treasure troves of science,” Schuster said. “We hope to add DNA-sequence data to the taxonomic data provided by many of the important specimens that define the species we know today.”