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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Rabbits aren't a good example, since they are non-indigenous.
"some ecologists predict that it could obliterate the entire wild populatio" is probably best interpreted as the customary plea for more research funds.
Razib--I didn't just pluck that line about extinctions from the ether. The authors of the new paper state: "models predict that the disease could lead to extinction of wild Tasmanian devils within 25 to 35 years."
They cite work by Hannish McCallum, the leading expert on the conservation biology of the Tasmanian devil. You can read about the model he and his colleagues used to derive their 35 year figure in this pdf (Ecohealth, 2007).
I'd certainly be interested in the comments you and your readers have about McCallum's model. But simply claiming that this is just a way to get research funds without bothering to read the research is just lazy.
ok, i checked the model. i see the logic, DFTD is not density dependent but rather frequency dependent (possibly). but again, the main issue i have is that in most cases extinctions due to 'disease' for many organisms are only an issue because of all the other things that humans have done (reduced habitat, etc.). you get an organism below a certain N and it is likely to randomly go extinct at some point anyhow. IOW, even if it was density dependent extinction would be likely sans proactive measures by humans to keep the devils going.
p.s. the original model it doesn't look like there's a mention of possible immunity (which would change the mortality parameter due to transmission obviously). makes sense since in 2007 there wasn't evidence of any immune individuals. but that's the problem with biological projections. the parameters can change.
Well now, ah'd git me one them im-mune studs. Cross 't with thirty fly bitchiz captured from "geographically and ecologically diverse locations". An then cross the lot of the female issue with a second immune stud, case it's one them "polygenic traits". An so on.
You reckon?