June 28, 2011

Scientists Sequence Genome Of Endangered Tasmanian Devil

Modern conservationists approach on whole-genome analyses of two Tasmanian devils drives efforts to save the species from extinction, a study revealed on Monday.

Tasmanian devils are a type of marsupial found exclusively in the wild of the Australian island-state of Tasmania that currently are suffering from a contagious cancer known as Devil Facial Tumor Disease (DFTD).

DFTD disfigures the victim and death comes from starvation or suffocation within months of infection. This unusual cancer was first observed on the east coast of Tasmania about 15 years ago; and has since spread westward very rapidly, threatening species with extinction, the study says.

"The disease is like nothing we know in humans or in virtually any other animal," says Stephan Schuster, a professor of biochemistry and molecular biology at Penn State University and lead researcher of the study.

"It acts like a virus but it actually is spread by a whole cancerous cell that arose in one individual several decades ago," Schuster explains. "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 our species very quickly," he says.

Researchers analyzed the genomes of one Tasmanian devil that died from DFTD and one healthy Tasmanian devil to develop a theoretical model to predict which individuals need to be kept in captivity in order to "maximize the chances of preserving enough genetic diversity for the species to survive."

The model suggests that if enough healthy Tasmanian devils were kept in zoos and other "protective custody" until the cancer ran its course and disappeared, then the captive animals could then be released back into their former habitat and the population would again begin to grow.

In order to accomplish this, the research team first sequenced the complete genomes of two individual Tasmanian devils. One belonged to a male named "Cedric," who naturally resisted two strains of DFTD, but finally died after being infected with a different strain of the cancer; the other belonged to a female named "Spirit," who contracted the cancer in the wild. The scientists also analyzed one of Spirit's tumors.

Researchers then examined the genomic data from both animals as well as the genetic characteristics of the tumor to create a model to determine which individual animals should be selected for captive breeding programs.

Currently, such a program is underway in Tasmania as well as on the mainland of Australia.

Schuster explains that choosing the right individuals to represent the entire species is critical for success.

"It might seem you'd want to choose only those individuals that are genetically resistant to the DFTD cancer," he says. "However, that would defeat the purpose of maintaining genetic diversity because, by definition, you'd be selecting a tiny subset of the gene pool. Instead, our model suggests a more balanced approach.

Schuster continues, "You don't want to put out just the one fire "“ cancer. Instead, you want to develop a pool of diverse, healthy individuals that can fight future maladies or even pathogens that have not yet evolved."

Researchers also compared the genetic data from the two Tasmanian devils to another 175 Tasmanian devils found in museums in order to figure out how much genetic diversity had been lost since Europeans settled in Tasmania in 1803.

"Museums are treasure troves of specimens collected in the last 250 years," says Schuster. "And, in fact, we can get DNA from hair shafts of a museum specimen."

He says that the DNA collected from hairs is virtually non-destructive, meaning specimens are not damaged visually during the process of removing a few hairs.

Analysis from the museum specimen yielded little change in genomic diversity of the Tasmanian devil over the last century.

"This is an important finding because it means that DFTD is not to blame for any lack of genetic diversity since the disease appeared only 15 years ago," says Webb Miller, a professor of biology and computer science and engineering at Penn State University who is part of the team.

He says, "It is crucial that we act as responsible stewards for the species, helping maintain what little genetic diversity it had before the DFTD epidemic struck."

The theoretical model for species preservation that is based on genome analysis could be extended to other endangered animals, which is about 25 percent of the world's land mammals, researchers say.

"We humans have contributed to the endangerment of many native species, so it's our responsibility to find a way to help fix things by giving nature a hand," Miller says.

The study is published in the journal Proceedings of the National Academy of Sciences.


Image 1: Zoo keeper and breeder Tim Faulkner holds a Tasmanian devil -- an endangered marsupial found in the wild in the Australian island-state of Tasmania. Credit: Stephan C. Schuster, Penn State University

Image 2: Successful breeding efforts are underway in mainland Australia and Tasmania to preserve a captive population of Tasmanian devils that are free from Devil Facial Tumor Disease. Credit: Stephan C. Schuster, Penn State University


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