Dr Elizabeth Murchison, Wellcome Trust Sanger Institute
Tasmanian devils are in danger of extinction, and to a contagious cancer that's spread between animals by biting. Itís called devil facial tumour disease.
Devil (A) with a tumour bites devil (B), introducing some of the tumour tissue in the process. The tumour then takes and devil (B), also develops the disease and will most likely die within a few months.
The disease has claimed now more than 60% of the Tasmanian devil population since it was first spotted 16 years ago. At first, no one knew what was causing it until Tasmania based genetic expert, Anne-Marie Pearse looked at the chromosomes in the cancers, and made a startling in discovery back in 2006.
Anne-Marie - Back then I was studying human cancer and I'm a bit of a crossbreed because I started out as a zoologist and switched to looking at chromosomes in human cancer which I did for 17 years. So, when this tumour came up, I walked in and told them I thought that maybe I could help. When we looked at the chromosomes in the actual tumour itself, we found that there were very, very mixed up chromosomes, just a complete mess. But the really interesting thing was, we found that they were exactly the same in every devil. Now, when you get something as complicated as the mix-up in these chromosomes in this cancer and when you can't find any sex chromosomes in the cancers in animals of either sex, you start to think, ďHang on, weíve got an infectious cell line.Ē
Chris - So, now we know the cause of the condition, scientists have been trying to work out how to stop it.
Hannah Siddle is based at the Pathology Department at Cambridge University where sheís been looking at the immune aspects of the disease. For instance, why isnít the foreign tumour tissue attacked by immune cells? Weíll hear from Hannah in a minute, but first, Elizabeth Murchison, also from Cambridge University, and the Sanger Institute, works on this disease, and has been looking at ways to reverse the decline in Tasmanian devil numbers. Elizabeth, tell us, for people not in the know, what actually is a Tasmanian devil?
Elizabeth - Well, most people in the UK often think that Tasmanian devils are a cartoon character that spins around and around. In fact, Tasmanian devils are the largest remaining marsupial carnivore. A marsupial is a mammal like a kangaroo that has a pouch and although most of us are familiar with marsupials like kangaroos and koalas, they also include carnivorous marsupials which eat meat, and the Tasmanian devil is actually the largest of these in the world.
Chris - How big is large?
Elizabeth - Well, itís about the size of a smallish dog. So, the males are actually about double the size of females and they weigh about, up to 13 or 14 kg.
Chris - And now, they're just confined to Tasmania, but were they once right across the Australian mainland?
Elizabeth - Yeah, there's fossil evidence that shows that Tasmanian devils used to be found all across the Australian mainland. They went extinct in the mainland of Australia about 1,000 or 500 years ago. Weíre not quite sure why and now, they're only confined on the island of Tasmania to the southwest mainland of Australia.
Chris - And a high proportion of them are succumbing to this disease.
Elizabeth - That's right. I mean, we donít know the exact numbers but it seems that more than 60 % of devils have disappeared as a direct consequence of these diseases spreading through their population. And in some areas on the east coast of Tasmania where the disease is best observed, more than 95% of the devils have already gone.
Chris - Are they beyond the tipping point or do you think we can save them?
Elizabeth - Well, itís really difficult to prevent this disease from continuing to spread in the wild because now, itís spread through almost all of the Tasmanian devilsí habitat. So, there's a few different options in trying to protect devils in the wild. One of them is trying to prevent the disease from spreading further either through building barriers such as fences to prevent the disease spreading, or by coming up with some kind of intervention vaccine or cure to try to keep the disease under control.
Chris - Which of those is proven the most successful has got the most support at the moment?
Elizabeth - Well, one of the most important conservation efforts that's going on at the moment is translocation project which is actually taking devils from the wild in Tasmania and putting them onto an island off the coast of Tasmania called Maria Island, which previously didnít have a devil population. But has now become a haven for disease-free devils and weíre hoping that devils are going to continue breeding there in the safety of isolation on the island without the disease, so that if the disease actually does wipe out the devils in the wild, they could be reintroduced from this island.
Chris - Will there be enough genetic diversity in such a small geographical area compared with the normal range they would enjoy where they're not confined to the island?
Elizabeth - Yeah, well that's a big concern and worry. Of course, when you take a small population of individuals and keep them breeding in captivity, you lose genetic diversity very quickly. And especially if you want to reintroduce this population to keep the species going, itís really important to capture that genetic diversity to keep species rigorous and healthy.
So, at the moment, weíre trying to map the kinds of genetic diversity which is already present in the devil population in order to select the best devils, to maximise the genetic diversity in the captive island population.
Chris - Because originally, people did think that perhaps the reason that this tumour problem was coming along was because there was a lack of genetic diversity. Do your results bear that out or are the devils that are left in Tasmania relatively inbred, or is there still quite good diversity at the moment?
Elizabeth - They are relatively inbred. They seem to have much less genetic diversity than many other wild species in Tasmania. However, we donít think that this is the reason for the spread of the disease. Actually, this is work from Greg Woods and Alex Kreiss in Tasmania who showed that they can do skin grafts of skin between devils that even appeared to be very genetically similar to each other, and that the skin grafts, were rejected by devils even though the tumours which are also from different devils were not rejected. So, there seems to be something very special about this tumour which is preventing it from being detected by the immune system.