Thursday, June 30, 2011

Tazmanian Devil Tumor-Disease UpdATE

DEVIL FACIAL TUMOR, TASMANIAN DEVIL - AUSTRALIA: (TASMANIA) UPDATE


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Date: Mon 27 Jun 2011

Source: New Scientist [edited]







Despite its ferocious nature, the Tasmanian devil is a creature faced

with extinction, the victim of a gruesome facial tumor disease. Now

the 1st genetic sequencing of these carnivorous marsupials has

revealed that we had a hand in their decline: centuries of human

interference left the devils stripped of genetic diversity and

vulnerable to disease.



This meant that when the parasitic face cancer dubbed "devil facial

tumor disease" appeared in 1996 it rapidly spread through the entire

population. As a result, the Tasmanian devil, or _Sarcophilus

harrisii_, population has fallen over 60 per cent since 1996.



The disease is transmitted by physical contact, mostly biting during

sex. It is almost always fatal and has spread across most of

Tasmania.



Due to the species' sharp decline, the International Union for the

Conservation of Nature (IUCN) has classed it as endangered. Some

studies estimate the marsupials could be wiped out within decades.



Marsupial sequencing

--------------------

To find out why they cannot fight the cancer, Stephan Schuster of

Pennsylvania State University in University Park and colleagues

sequenced the genomes of 2 Tasmanian devils, the 1st Australian

marsupials to be sequenced.



Schuster chose animals from opposite ends of the island, which should

have been as genetically distinct as devils get. But he found they

were pretty similar: their genomes only differed at 915 000 sites. A

similar comparison showed that 2 humans from China and Japan differ at

3 257 000 sites, says Schuster.



Genetic analysis of a further 175 wild animals and 7 museum specimens

showed that devils have had a low genetic diversity for over 100

years.



Humans had a heavy hand in this. First the devils were wiped out in

mainland Australia by dingoes brought in by settlers, then those that

remained in Tasmania were hunted as pests, causing several population

crashes. As their genetic diversity was slashed, the devils were left

vulnerable to disease.



This is clearly at the root of their problems, says Katherine Belov

of the University of Sydney, Australia. "Devils are essentially

immunological clones, so tumors pass between them without triggering

an immune response," she says.



The Australian and Tasmanian governments have set up a conservation

programme, capturing disease-free devils to establish an "insurance

population". Housed at sites like the Devil Ark in Somersby, New South

Wales, these devils could re-populate Tasmania if the wild population

is wiped out.



Missing diversity

-----------------

But Schuster says the captive population is missing some of the wild

population's diversity, such as it is. He found 7 subtly distinct

populations on the island and says individuals from each must be

included. But as nobody has genotyped the captive population we don't

know what is missing. Based on partial information on where the

individuals were collected, Schuster suspects the captive genotype is

not as diverse as it could be.



Having a large genetic diversity is essential for any captive

breeding programme, agrees Craig Hilton-Taylor of the IUCN, based in

Cambridge, UK. Schuster says conservationists need to look at genetic

diversity when they assess a species' wellbeing. He points out that

before the facial tumour disease appeared, the IUCN considered devils

to be of "least concern" because their population and habitat were

reasonably large. In fact they were genetic sitting ducks, says

Schuster.



The IUCN doesn't require its scientists to do genetic testing on

species they are assessing, although the information is used if they

do. Hilton-Taylor agrees the information can be invaluable, but says

systematic testing would be difficult and expensive.



Journal reference: Proceedings of the National Academy of Sciences,

DOI: 10.1073/pnas.1102838108 [abstract available at

].



[Byline: Michael Marshall]



--

Communicated by:

ProMED-mail





[This article does not mention if there were any sequences of

Tasmanian devils in some other zoo in the world that might lend

genetic diversity or be a tumor free source of genetic material. But I

cannot remember if the Tasmanian devil has ever been sent to other

zoos - Mod.TG]



[Photos of Tasmanian devils can be seen at

.

Facial tumor at:





Tasmania can be located on the HealthMap/ProMED-mail interactive map

of Australia at . - Sr.Tech.Ed.MJ]



[see also:

2010

----

Devil facial tumor disease - Australia (TS) 20100102.0019

2008

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Devil facial tumor disease - Australia: (TAS) 20080718.2174

2007

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Devil facial tumor disease - Australia (TAS) (02) 20071004.3289

Devil facial tumor disease - Australia (TAS) 20070218.0616

2006

----

Devil facial tumor disease - Australia (TAS) (02) 20061024.3051

Devil facial tumor disease - Australia (TAS) 20060201.0328]

.................................................sb/tg/mj/jw

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