Science News - July 30, 2011

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The study reveals more details about
the genetic diversity of current Tasma-
nian devil populations. While research-
ers have long known that the devils have
low levels of genetic diversity, the new
work shows that overall devil diversity
is about 20 percent of that in humans.
The team’s analysis of DNA from
museum specimens dating back to
1874— at least 100 years before the
infectious cancer arose —finds that
devils have long had that
low level of diversity. The
tumor has not reduced the
amount of diversity in wild
populations, researchers
discovered after testing
168 wild devils.

infectious cancer, which started in a single long-dead devil and has since swept over more than half the island. Cedric survived t wo attempts to infect him with the facial tumor as part of efforts to better understand the disease, but finally succumbed to a third strain. Spirit was already infected with five tumors and was near death when she was captured.

Researchers hope that comparing the two animals’ genomes, consisting of all the DNA contained in the cell nucleus, will show why Cedric was partially immune to the fatal cancer while Spirit and so many others are not.

Cedric, a Tasmanian
devil partially immune
to an infectious cancer,
was one of the two
devils whose genomes
have been deciphered.

The initial analysis of the two genomes doesn’t provide a clear answer, but scientists suspect that most devils have variants in certain genes that make them susceptible to the tumors.

That finding strikes a
hopeful note, says evo-
lutionary biologist Anne
“The really exciting discoveries are yet
to come,” says Katherine Belov, a geneti-
cist at the University of Sydney who was
not involved in the study. “We are very
excited to be able to jump in and start
mining this genome.”
Low diversity might affect how
well devils fight off the infectious can-
cer, though. Because the devils are so
genetically similar to one another, their
immune systems may have trouble
recognizing tumor cells passed on by
another devil as foreign.

Some scientists have proposed that instead of being passed directly from one animal to another, the cancer might be transmitted by viruses during bites. But a closer look at one of Spirit’s tumors showed that the cancer cells definitely came from another devil.

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Schuster says that even though low genetic diversity has probably made devils vulnerable to the cancer, it’s not insurmountable. Breeders should use genetic tests to match up relatively diverse mating pairs of devils instead of hoping that randomly choosing animals will maintain the fragile diversity, Schuster says. He thinks that employing the right strategies can save the Tasmanian devil.

“This is probably one of the only cases where human intervention, doing all the right things, can prevent a species from going extinct,” Schuster says. s

Tasmanian devil
diversity detailed
First genetic blueprints don’t
explain cancer vulnerability

By Tina Hesman Saey

Two new complete sets of Tasmanian devil genetic blueprints hold some good news and bad news for the species. The bad news is that the marsupial’s genetic diversity is among the lowest known for any species. The good news is that the devil’s low diversity has a long history and may not be reason for as much concern as once thought.

This low genetic diversity “does not
mean the species is doomed,” says gen-
omicist Stephan Schuster of Pennsylva-
nia State University in University Park.
“If you maintain the entire diversity this
can still be a viable species.”
A team of researchers deciphered the
genetic blueprints of two Tasmanian
devils named Cedric and Spirit that
hail from opposite ends of Tasmania,
the team reports online June 27 in the
Proceedings of the National Academy of
Sciences. The two devils differ in their
response to the infectious cancer that
has decimated wild devil populations.

Cedric was one of the few devils whose immune system could fight off the

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92

Average pairwise differences

80

60

40

20

77

67

Low diversity Not all endangered species (darker bars) exhibit low genetic diversity. Gorillas, pandas and polar bears are all relatively diverse, according to a measure that counts differences between pairs of individuals in mitochondrial DNA, a separate snippet of DNA passed down only along the maternal line.