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Health

Contagious Tasmanian Devil cancer

Gene ExpressionBy Razib KhanJanuary 1, 2010 6:24 AM

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Carl Zimmer has a nice write up of the a new paper in Science which characterizes the nature of the cells which are manifest during devil facial tumor disease. The Tasmanian Devil Transcriptome Reveals Schwann Cell Origins of a Clonally Transmissible Cancer:

The Tasmanian devil, a marsupial carnivore, is endangered because of the emergence of a transmissible cancer known as devil facial tumor disease (DFTD). This fatal cancer is clonally derived and is an allograft transmitted between devils by biting. We performed a large-scale genetic analysis of DFTD with microsatellite genotyping, a mitochondrial genome analysis, and deep sequencing of the DFTD transcriptome and microRNAs. These studies confirm that DFTD is a monophyletic clonally transmissible tumor and suggest that the disease is of Schwann cell origin. On the basis of these results, we have generated a diagnostic marker for DFTD and identify a suite of genes relevant to DFTD pathology and transmission. We provide a genomic data set for the Tasmanian devil that is applicable to cancer diagnosis, disease evolution, and conservation biology.

In Carl's article, he reports:

The cancer, devil's facial tumor disease, is transmitted when the animals bite one another's faces during fights. It grows rapidly, choking off the animal's mouth and spreading to other organs. The disease has wiped out 60 percent of all Tasmanian devils since it was first observed in 1996, and some ecologists predict that it could obliterate the entire wild population within 35 years.

I think that the ecologists need to be careful here, as the public might think that the cancer itself is going to be the immediate proximate cause of extinction. Rather, it seems more likely that the disease will reduce the numbers of the devils, of which there are on the order of 10 to 100 thousand on the island. And small populations, say less than a 1,000, are subject to random fluctuations in population size which could drive them to extinction (imagine a short-term climatic regime which reduces the food supply). It seems that some individuals are already immune to the disease, so over time if nature took its course the population would probably bounce back. Projecting extinction because of disease necessarily and sufficiently is just part of the linear fallacy, which isn't really good at predicting over the long term in biological contexts. Australia still has rabbits. It's called evolution.

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