Threatened Species of the Week- Tasmanian Devils and Transmissible Cancer

by Lucy Hagger

Welcome to the very first post in my new feature: Threatened Species of the Week!

Which species will have the honour of being the first threatened species on my list? I was thinking of ways to choose this first species and dabbled with a few ideas. I decided to look into a threatened species that comes with a very interesting story to liven things up a little.

Because of this I decided to go for.. drum roll please.. the Tasmanian Devil (Sarcophilus harrisii)! How terribly exciting.. right so let’s give you some facts about this creature and why it is threatened by extinction.

Tasmanian Devils are listed as Endangered by the IUCN Redlist classification which is all explained in a previous post which you should have a look at if you haven’t already. These marsupials are found wild only in Tasmania, an island off the south coast of Australia.

Their numbers have been declining for some time for numerous reasons, however the most devastating culprit is a disease which is rapidly wiping out the isolated populations. This disease is called Devil Facial Tumour Disease (DFTD) and is a kind of cancer. The cancer is common throughout 60% of the Tasmanian Devils’ natural range and is spreading at a rate of 7-50 km per year.

Studies of these tumours stunned scientists as they realised something very bizarre was going on. If you compare the tumours of people suffering from the same kind of cancer the DNA of the cancerous cells are specific to that individual. Essentially each person’s tumour cell DNA is different.

However, studies of the tumour cells of these Tasmanian Devils found that the DNA was almost identical. Now this makes very little sense as tumour cells are those which have mutated from that individual’s normal healthy cells. So how on Earth can all of these different diseased Tasmanian Devils have the same DNA in the cells of their tumours??

The answer to this question is that the cancer is being directly transmitted from infected individuals to uninfected individuals. But how can this be? Cancers don’t spread from person to person, they occur as a consequence of genetic and environmental factors. So this existing transmissible cancer occurring in Tasmanian Devils is something incredibly intriguing.

Research and observation soon found the key to this unusual transmissible cancer. The temperament of the Tasmanian Devil created by Warner Bros. was based on fact, with real Tasmanian Devils being incredibly aggressive creatures. They regularly fight and this characteristic is the root to why these Devils share the same tumours.

The tumours that form as a result of DFTD form on the face, commonly around the mouth and jaw. When an infected Devil fights and bites their opponent the teeth essentially act as needles, injecting the cancerous cells into the flesh of the other Devil. So these Devils are directly transmitted this cancer to each other.

In the region of Tasmania where most Devils are found, roughly 30% of the total population was lost within the first 3 years after the disease’s arrival, and the adult population declined by 50% each year. From this information it has been predicted that within 10 years of the disease’s arrival, the devils in that region will be extinct.

Already the population has predicted to have declined from 130 000-150 000 individuals in 1987 to 10 000-25 000 in 2007. Estimates of the whole Devil range predict that over 70% of the total population will be lost in less than 10 years.

The tragic thing about this situation is that, although the cause of decline is well understood, very little can be done to prevent it. There is no cure for this cancer and the fighting nature of the devils means that the disease will continue to spread. To make things worse devils are commonly killed by vehicles, dogs and foxes in the region and the low genetic diversity that exists as the population bottlenecks with further threaten the devils in the future.

Efforts are being done to protect the devils and attempt to limit the spread of the disease in the currently unaffected regions. The Save the Tasmanian Devil Program works to research DFTD and maintain the existing population. Devils are being reared in captivity to act as a kind of insurance population as the wild devils continue to decline. The program is also trying to develop resistance to the disease through rearing programs and also are developing a vaccine to treat DFTD, however the use of the vaccine would not be feasible for wild devils.

The situation is not looking good for Tasmanian Devils and in my opinion the wild population will become extinct and the “insurance” devils will attempt to make up for the loss with reintroductions to the wild.

Right.. well I hope you enjoyed the first instalment of Threatened Species of the Week and will be reading again next week!

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