Devil Facial Tumour Disease

The seemingly needless “u” in “Tumour” is how it is written in reference to the disease, regardless of the country.

By Michael Hawkins

Devil Facial Tumour Disease is a particularly nasty cancer afflicting the Tasmanian devil population of Tasmania right now. It is spread by devils biting each other in the face and has been fatal for upwards of 50% of the population. Recent research has shed some light onto its origins.

Australian scientists found that the disease originates in Schwann cells, which protect peripheral nerve fibers. This has opened the door to the discovery of a genetic marker which can be used to diagnose the cancer.

What they also found was that in each subject, the disease was fundamentally the same. That is, the cancer does not originate in the individual devils, but instead comes from one common source, some long deceased devil. This means the disease can effectively be regarded as a separate organism, free to undergo its own evolution. Of course, its evolutionary ‘goals’ do not jive with the evolutionary ‘goals’ of its host, so there is an obvious conflict. (Please note the scare quotes around “goals”. The term is metaphorical.)

The cancer may become more and more virulent, allowing it to spread further and faster around the island. That could mean the end of both the devils and the cancer. Eventual death is not a very good long term evolutionary strategy, but then natural selection does not have any sort of foresight. Alternatively, the cancer could become less virulent so that its host could survive longer, thus offering the devil a greater chance to pass the disease along. Either way, the devils are out of luck.

One question this indirectly raises is if this susceptibility to cancer has anything to do with poor contact inhibition, the mechanism by which cells stop reproducing upon coming into contact with each other. Cells that don’t do that are called cancer. Most animals have one gene for this (p27), but naked mole rats have two (p27 and p16). This constitutes an extra barrier against cancer; as such, naked mole rats have never been observed to have developed cancer. Ever.

This means that at least one theoretical avenue of research into the cancer afflicting devils could be into the efficacy of their p27 gene: it may not offer the same effectiveness it does in other animals, especially considering the devil’s susceptibility to cancer in general.

But wherever the research should go, the dwindling Tasmanian devil population clearly needs help. And soon.

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