Readers may remember a post from last December about the sad decline of Tasmanian devils due to a highly contagious and almost invariaby fatal facial cancer that was devastating their already low numbers. Now, however there is some slightly better news - the devils are rapidly evolving under this intense selection pressure to become resistant to this cancer.
The cancer itself is believed to have arisen as tumour that is not recognised by the devils' immune system, possibly because of a high level of local inbreeding because of an already severely reduced population leading to a lack of genetic diversity. The devils are highly susceptible to this cancer because of their habit of aggressively biting one another on the face. Since it was first noticed about 20 years ago it has killed about 80% of the population. It is almost 100% fatal and is the most deadly of only three known transmissible cancers.
But, despite fears that the devils were on the verge of extinction, a few have survived and it is in these that there are signs of genetic changes in seven locations in their DNA, five of which are associated in other species with cancers and immunity. The discovery was made by Andrew Storfer, professor of biology with washington State University, and an international team of scientists. Their findings were published yesterday in Nature Communications.
Although cancer rarely acts as an infectious disease, a recently emerged transmissible cancer in Tasmanian devils (Sarcophilus harrisii) is virtually 100% fatal. Devil facial tumour disease (DFTD) has swept across nearly the entire species’ range, resulting in localized declines exceeding 90% and an overall species decline of more than 80% in less than 20 years. Despite epidemiological models that predict extinction, populations in long-diseased sites persist. Here we report rare genomic evidence of a rapid, parallel evolutionary response to strong selection imposed by a wildlife disease. We identify two genomic regions that contain genes related to immune function or cancer risk in humans that exhibit concordant signatures of selection across three populations. DFTD spreads between hosts by suppressing and evading the immune system, and our results suggest that hosts are evolving immune-modulated resistance that could aid in species persistence in the face of this devastating disease.
Brendan Epstein, Menna Jones, Rodrigo Hamede, Sarah Hendricks, Hamish McCallum, Elizabeth P. Murchison, Barbara Schönfeld, Cody Wiench, Paul Hohenlohe, Andrew Storfer.
Rapid evolutionary response to a transmissible cancer in Tasmanian devils.
Nature Communications, 2016; 7: 12684 DOI: 10.1038/ncomms12684
Copyright © 2016, Rights Managed by Nature Publishing Group, reprinted under Creative Commons Attribution 4.0 International License (CC BY 4.0)
This is good news for this, the largest carnivorous marsupial but is actually expected though by no means certain, by the Theory of Evolution by Natural Selection. Intense selection pressure such as this would be expected to concentrate any genes for resistance in the surviving population. But let's, just for fun, try to apply the creationist intelligent (sic) design notion to this situation:
Are we to believe that an intelligent designer would design this particularly nasty cancer and arrange for it to be transmitted this way? What would be the purpose of this and how does it fit with the notion that this designer is somehow all-loving and worthy of adulation? As though that piece of nonsense is not hard enough to swallow, where is the intelligence in then designing resistance to the cancer it had designed for whatever ineffable and malevolent reason? If the designer had wanted to breed a population of cancer-resistant Tasmanian Devils why not simply design them resistant in the first place, and why design a cancer it wants the devils to be resistant to? Absolutely no sense or sign of intelligence there and absolutely no sign of omni-benevolence either.
Again, the attempt to force-fit observable reality into a primitive Bronze Age creation myth crashes and serves only to illustrate the gullible credulity of those who fall for the hoax and the dishonesty of those who perpetrate it.
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