Author: Carl Zimmer
Source: The New York Times
Date: 21 January, 2013
In November, a team of biologists journeyed to Maria Island, three miles off the Australian island state of Tasmania, taking with them 15 plastic cylinders. They loaded the cylinders into S.U.V.’s, drove them to an abandoned farm and scattered them in the fields.
Before long 15 Tasmanian devils emerged from the containers, becoming the first ever to inhabit the island.
“All indications are that they’re doing very well,” Phil Wise, a government wildlife biologist who leads the project, said of the devils — fierce-looking, doglike marsupials that have become an endangered species on the much larger island for which they are named.
This spring the team plans to take more devils to Maria (pronounced ma-RYE-uh). The goal is to establish a healthy colony that will endure for decades to come. The stakes of the project are high: the survival of the entire species may depend on it.
Many species are threatened with extinction, but the Tasmanian devil faces a singular enemy: an epidemic of cancer. A type of facial tumor has in effect evolved into a parasite, with the ability to spread quickly from one devil to another, killing its victims in a few months.
“We have very little time to save the species,” said Katherine Belov, a biologist at the University of Sydney.
An international network of biologists has spent the past decade figuring out this new kind of disease. “It’s been quite a struggle just to learn some of the basics,” said Elizabeth Murchison, of the University of Cambridge in England.
But recently Dr. Murchison and other experts have gained important insights into how the cancer evolved into a parasite. Some scientists are now trying to translate that knowledge into a treatment, perhaps a cancer vaccine.
There is no guarantee that these projects will save the devils, so Mr. Wise and his colleagues are setting up a drastic Plan B: they are establishing Maria Island as a cancer-free refuge for wild Tasmanian devils.
Then, if the devils die out in Tasmania, Dr. Belov said, “the disease will be gone from the mainland, and then they can be introduced back in the wild.”
Biologists first encountered the cancer in the late 1990s. The tumors grew on the devils’ faces or inside their mouths, and within six months the animals were dead. The first cases appeared in eastern Tasmania, and with each passing year the cancer’s range expanded westward.
When scientists examined the cells in the tumors, they got a baffling surprise. The DNA from each tumor did not match the Tasmanian devil on which it grew. Instead, it matched the tumors on other devils. That meant that the cancer was contagious, spreading from one animal to another.
There are only a few reports of humans developing cancer from other people’s tumors hidden in transplanted skin or other organs. Only one other example of contagious cancer is known from the natural world, a tumor in dogs.
Dr. Murchison led a team of researchers who sequenced the entire genome of two tumor cells. They published the sequences last February, and since then they have launched a project to sequence hundreds more genomes of Tasmanian devil facial tumors.
Their studies and others like them are revealing how the Tasmanian cancer got its start. It probably originated in the 1980s or early 1990s in a single animal, most likely a female. A nerve cell in her face underwent a drastic mutation: its chromosomes shattered and then stitched themselves back together.
“The cell was still able to function, because there wasn’t too much DNA lost,” Dr. Belov said. “It’s a bit of a freak of nature.”
The cancer then spread to other devils by taking advantage of their behavior. The animals frequently fight, biting their opponents’ faces. During these battles, Tasmanian devils sometimes bite off bits of a tumor. The cells slip into the attacker’s own bloodstream and travel to its face. There they grow a new tumor.
Dr. Murchison and her colleagues have identified some 20,000 mutations in the tumors that are not found in normal Tasmanian devil DNA. But they do not know which of those mutations originally gave rise to the cancer.
Recent research is revealing that the cancer has been evolving. “Up until a year ago we thought the tumor was completely stable,” Dr. Belov said. “But now we know that’s not the case.”
She and her colleagues recently examined cancer cells collected from Tasmanian devils in 2007 and 2008, comparing them with cells collected from 2010 to 2012. They surveyed molecular caps that cover some genes, known as methylation marks. These marks can keep genes from producing proteins.
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