A revolutionary species-preservation approach based on whole-genome analyses of two Tasmanian devils（袋獾） -- one that had died of a contagious（感染性的） cancer known as Devil Facial Tumor Disease (DFTD) and one healthy animal -- has been used to develop a theoretical model to predict which individuals would need to be kept in captivity to maximize chances of preserving enough genetic diversity for the species to survive. The research helps to formulate one possible plan of action to prevent the extinction of the Tasmanian devil -- a marsupial（有袋类动物） found in the wild exclusively in the Australian island-state of Tasmania. The research model also may be extended to other endangered species. The team, led by Stephan Schuster, a professor of biochemistry and molecular biology at Penn State University; Webb Miller, a professor of biology and computer science and engineering at Penn State University; and Vanessa Hayes of the Venter Institute in San Diego, includes other scientists at institutions and universities in Australia, Denmark, and the United States. The results of the study will be published in the journal Proceedings of the National Academy of Sciences. Additional information about the team's research is posted at the project website, http://tasmaniandevil.psu.edu. DFTD, which disfigures the victim and causes death from starvation or suffocation（窒息） within months, is an unusual sort of cancer that first was observed on the east coast of Tasmania just 15 years ago, and since has spread rapidly westward, threatening the species with extinction. "The disease is like nothing we know in humans or in virtually any other animal. It acts like a virus but it actually is spread by a whole cancerous cell that arose in one individual several decades ago," Schuster explained. "This malignant cell is transferred directly from one individual to another through biting, mating, or even touching. Just imagine a human cancer that spread through a handshake. It would eradicate（根除，消灭） our species very quickly." The scientists explained that if a number of healthy Tasmanian devils were kept in zoos and other facilities in "protective custody" until the tumor ran its course and disappeared in the wild, then the captive animals could be released back into their former habitat and the population could begin to grow anew. "However, it's not just a matter of scooping up a few individuals at random and locking them away," Miller explained. "Our team developed a smarter, more calculated approach: We asked ourselves, which individuals would be the best candidates for 'protective custody,' and what criteria would we use to make those determinations? We soon realized that the answer was to compile genetic data and to analyze it in novel ways."

The team approached the extinction problem on two fronts. The first was to sequence the complete genomes -- 3.2 billion base pairs each -- of two individual Tasmanian devils. One was a male called "Cedric," who had a natural resistance to two strains of DFTD, but succumbed（屈服，死） after being infected with a different strain of the disease last year. The other was a female called "Spirit," who had contracted the vicious（恶毒的） cancer in the wild. In addition, the scientists sequenced the genome of one of Spirit's tumors. Because the two animals had originated in the extreme northwest and southeast regions of Tasmania, respectively, they represented the maximal geographic spread of the species -- a measure that is used as an approximation（近似） of genetic diversity. The researchers then began an analysis of the genomic data from the two animals, and of the genetic characteristics of the tumor. Using these data, they created a model that could determine which individual animals should be selected for captive breeding programs, such as the ones currently underway in Tasmania and on mainland Australia.