Devils have declined by 90% on the Freycinet Peninsula in Tasmania. The Devil facial tumour disease is a contagious cancer. This is unusual for a cancer. The infection is spread as devils bite each other. The tumour originated in Tasmania’s north east in the 1990s and is spreading. The spread is assisted by the devils’ behaviour and their low genetic diversity. As Menna Jones explains, devils play an important role as a top predator. As the devils decline, feral cats are increasing and there is concern about foxes. Menna Jones describes the latest management strategies.
The Science Show - Transcript - 3 September 2011
Robyn Williams: The Tasmanian Devil is fighting for its very existence. A terrible disease, hideous to behold, is killing hundreds of creatures and perplexing the scientists. This is Dr Menna Jones, just returned from the field outside Hobart.
Menna Jones: I have literally just returned out of the mud and the rain in the bush, setting traps for Devils at my long-term field site on the Freycinet Peninsula.
Robyn Williams: Did you find any?
Menna Jones: We didn’t attract any Devils this morning. We’ve had more than 90% population decline of Devils up there. Ten years ago on the peninsula, which is 150 square kilometres, we would have trapped about 150 Devils, and now we anticipate getting around about ten or even less in a two-week field trip.
Robyn Williams: And when you do find them, how many have got the disease?
Menna Jones: 50% will have the disease. We’ll probably catch two or three adults in total, a lot of the juveniles will also have the disease.
Robyn Williams: Tell me, for people on the mainland, who don’t understand so much about what’s going on how is the disease spread on the island of Tasmania at the moment?
Menna Jones: The Devil facial tumour disease is a very unusual and very rare contagious cancer. Usually cancer is not something you catch, it is something which dies with its host, but this cancer, the tumour cells themselves are the infectious agent and they are spread by biting from Devil to Devil, and the transfer of live tumour cells which then grow into new tumours in the other host [another devil].
Robyn Williams: And from the north to the south of the island is there any distribution difference at all of the tumour, those who are healthy and those who are not?
Menna Jones: There is a difference in the underlying genotypes of the Devils, the genetic structure of the Devils between the eastern half of Tasmania and a smaller population in the north-west. The tumour originated, it arose in the north-east, and it is genetically nearly identical to the Devil in the north-east. After all, it is actually a degenerate piece of Devil tissue, it’s an obligate parasite on the Devil which is a piece of Devil tissue, so it is genetically identical to eastern Devils. But we have Devils in north-western Tasmania with different genotypes, and we have been working at a study site up near Cradle Mountain where the tumour…as it’s spreading westwards it’s encountering these different Devil genotypes for the first time. And we are seeing very different patterns of the epidemic up in the north-west.
Compared to eastern sites we are not seeing population decline, we’re not seeing loss of older animals out of the population. We have very low prevalence [of the cancer], and the Devils seem to be surviving much longer with the tumours. In eastern Tasmania most Devils are dead within three months of a visible tumour arising. In the north-west we have individuals that are living for over 12 months with the tumour disease.
Robyn Williams: But why did it erupt, do you think, in recent years as it has?
Menna Jones: The actual cause of the tumour, the original case of the tumour in the original Devil that got this cancer, we really don’t know. It could be a genetic predisposition in Devils, in all of the carnivorous marsupials, to getting cancer, they may have a fairly unstable genome. It may have been exposure to carcinogens or a cocktail of carcinogens in the environment.
Robyn Williams: But suddenly in recent times, bang, there it was.
Menna Jones: It [the cancer] emerged sometime in the early to mid-‘90s. We know that it’s a new disease, it hasn’t been seen before. We also know that Devils have had low genetic diversity for a long time, and this and their biting behaviour where there is intimate contact, flesh to flesh between individuals, provides optimal conditions. That and the low genetic diversity provide optimal conditions for the spread of a contagious cancer once it gets going. So the original Devil that got this cancer, it had a cancer, and because of the low genetic diversity and because these animals bite each other a lot, it managed to spread that cancer to other Devils, and now it’s just spreading as a clonal cell line from Devil to Devil right across Tasmania.
Robyn Williams: Obviously the Devils, being a top carnivore, especially in Tasmania, have an effect on the environment, the ecology where they live. Have you noticed anything dramatic with other plants and animals around them as a result of their diminishing numbers?
Menna Jones: We are studying this and it is of great concern. Remember too that the Devil was originally a mesopredator. We had Aboriginal Tasmanians and we had the thylacine which were top predators in the environment, but they were long lost in terms of their effective ecological function in the environment. The things that we have seen, we know that we’re getting a rise in feral cat numbers, we know that we have foxes in the state, and there is a very dedicated eradication effort for foxes. But decline in Devil populations is creating exactly the perfect conditions for an eruption of foxes.
Robyn Williams: Some people have said that there is no evidence that foxes are here.
Menna Jones: There is plenty of evidence that foxes are here, and they occur over two-thirds of Tasmania, everywhere we would expect them to live based on habitat, and we know they are breeding. And the best evidence now comes from searches in the environment and picking up faeces from which the DNA can be analysed and identified to species.
Robyn Williams: And these are foxes that some idiot brought quite recently.
Menna Jones: It’s a little over ten years ago, around about 14 years ago, we believe it was a malicious introduction to the state, and it could well be one of the biggest ecological catastrophes in recent times in Australian conservation.
Robyn Williams: What sort of effects are you seeing already?
Menna Jones: It’s a little bit hard to tell. Until foxes reach very high densities they are nearly impossible to detect in the environment. We know that foxes are there in low density, they might be in medium density, we don’t know. They’re starting to turn up as roadkills, which is not a good sign. We have in recent years seen quite a dramatic decline in two of our medium-sized marsupials, the eastern quoll and we think also the Tasmanian bettong. This could be mesopredator release as a result of the Devil decline. The eastern quoll decline is very tightly correlated with Devil decline but it is also strongly influenced by rainfall and particularly the severe drought that we’ve had in the last decade. But it could be foxes, there could be a very quiet effect of foxes right across the landscape that we may not detect until it is nearly too late.
Robyn Williams: And so the quest is to bring the Devils back and presumably you’ve got populations in some parts of the island that you bring to other parts where a different kind of genome is manifest which is more vulnerable, and also perhaps on the mainland you can have reservoirs. What’s the plan?
Menna Jones: The really critical thing is that we try to bring Devils back into the Tasmanian ecosystem to fulfil their ecological role as a top predator in suppressing cats, suppressing foxes, suppressing over-abundant macropod prey, wallabies particularly, wallabies and pademelons. This really should drive our management strategies, and one management strategy is to put them away safe in captive insurance populations where in the event of extinction in the wild we could reintroduce them in perhaps 50 years time. We hope we don’t get to go down that route.
We also are focusing our research on looking for patterns of disease resistance or reduced impact of the disease, reduced epidemic in parts of the state. What we are looking for there is if there is anything in the genetics of the Devil that could confer resistance or resilience at a population level to the disease. We are also watching the tumour very closely because the tumour is evolving, and to see if the tumour might evolve towards something that is less virulent and less devastating for the Devil.
So the alternative scenario is that the Devil and the tumour will both evolve and perhaps co-evolve, and they may learn to live together over time. We’re not pinning our hopes on that, but this is where much of our research is focused, is on the interaction between the tumour genetics and the Devil genetics at the moment, and our study site up in the north-west around that region is where we are focusing our research. But with all of that we do need to focus on keeping Devils living in wild situations in wild populations so that if we do need to supplement or reintroduce animals into the wild we have an animal that is still a wild Devil and is not some sort of evolved captive animal that wouldn’t be as suitable for return to the wild.
Robyn Williams: But how many do you have on the mainland in reserve?
Menna Jones: We have Devils in captive populations on the mainland, and matter of hundreds at the moment, and some in smaller free-range enclosures. We have four larger free-range closures in Tasmania and several hundred Devils in wildlife parks and in the state government facility.
Robyn Williams: And the ones on the mainland, are there more or less disease free?
Menna Jones: All of the Devils that are in captive populations are disease free. What we need to be doing now is establishing healthy, disease-free, safe, secure, wild populations on islands and perhaps very large fenced enclosures on the mainland of Australia as well.
Robyn Williams: It’s only a dog that’s the other example of its occurrence in the whole of the world, isn’t it.
Menna Jones: That’s correct. The only other case in nature is a dog tumour that is transmitted during mating. That is thought to have arisen 10,000 to 15,000 years ago and it probably originated in a genetically restricted population in the same way that the Devil cancer did. But that is now a highly evolved cancer and it has spread into dog populations across the world where it is now in genetically diverse populations and the cancer has evolved, initially to make itself invisible to the dog’s immune system but after a period of time to make itself invisible. Diseases that are too virulent will drive themselves to extinction. If they kill their host too fast, they die out, and the dog cancer has evolved to get around that problem. So after a period of time it shows itself to the dog’s immune system and the dog becomes immune for life, but it survives, but it has already passed the cancer on.
Robyn Williams: Dr Menna Jones at the University of Tasmania, and I see she is a finalist in the Eureka Prizes coming up on Tuesday, part of a team doing that frontline work.