A contagious cancer is threatening to wipe out the Tasmanian devil. A big problem is that the devils are all so genetically similar. Breeding programs and genome mapping are underway, and there have already been surprises.
When we think of the Tasmanian devil, with its ferociously sharp teeth and equally powerful claws, it may be difficult to remember the species is under threat. As the world’s top marsupial predator, what could be causing its numbers to dwindle?
The answer is an extraordinary cancer called devil facial tumour disease (DFTD) which is responsible for slashing the devil population by 85 percent since 1996. “Part of the reason DFTD has been so devastating is the devils’ lack of genetic diversity,” says Professor Katherine Belov (CertEdStud ’10), University of Sydney Pro-Vice Chancellor (Global Engagement) and head of the Australasian Wildlife Genomics Group (AWGG). The genetics of both the devil and the cancer are providing Professor Belov’s team with plenty of places to look for solutions that might save the devils.
“When the thylacine, or Tasmanian tiger, became extinct in the 1930s, the Tassie devil took up its place as the dominant marsupial predator,” says Dr Carolyn Hogg (PhD (Vet Science) ’06), research manager for Professor Belov’s group. “Being the top predator makes the devil a hugely important part of the Tasmanian ecosystem.”
The facial tumour disease is remarkable in that it is a transmissible cancer. It is spread when the devils bite each other, predominantly on the face, hence the name. It’s one of only four known cancers that can be spread from host to host. The lack of genetic diversity adds to the threat.
“The more genetic diversity a species has, the better its chances of surviving and adapting to future change,” Professor Belov explains. But the devils, which are so genetically similar they are sometimes referred to as “clones”, have such low diversity that their population numbers have crashed numerous times in the past.
Devil facial tumour disease was first spotted in north-east Tasmania, but it has since spread to the south and west. In 2009, it was estimated that within 25 years the entire devil population would be gone unless something was done to prevent it. Enter Professor Belov and her team at the University of Sydney, who have been working since 2007 on both the disease itself and the genetics of the Tasmanian devil insurance population (a captive group of about 700 devils).
University of Sydney PhD student Emma Peel (BAnVetBioSc ’13), who is a researcher within the group, made a surprising discovery that could not only cure the devils’ cancer, but may also have incredible benefits for humans.
Peel, like many other researchers, was confounded by the idea that young devils were not succumbing to the cancer like their older counterparts. Devils have very short pregnancies – about 18 days – and their young are born extremely underdeveloped and with little immunity, explains Peel. “When the devils are born they go straight to their mother’s pouch, which is full of potentially harmful bacteria,” she says. “We started thinking, ‘how are these baby devils, with essentially no immune system, surviving in their mothers’ pouches?’
”What Peel found was that the devils’ breast milk is packed with unique antimicrobial peptides, known as cathelicidins, which may protect the babies from facial tumour disease.
The peptides were also expressed through the skin of the devils’ pouch, providing natural immunity. “Cathelicidins are found in other mammals,” says Peel, “and they’ve been studied quite extensively in humans, where they do have anti-cancer properties.”
During testing, Peel discovered that the cathelicidins can kill two types of dangerous and increasingly drug-resistant bacteria: methicillin-resistant Staphylococcus aureus (commonly known as golden staph) and vancomycin-resistant Enterococcus faecalis. “We’ve been doing so much work on DFTD, that to find something that could be used one day to help humans is a really great outcome,” says Peel. While no research has been performed on live devils to see whether the peptides can combat the disease, this is the next step for the team. In the petri dish, at least, things look promising.
For now, the focus is on securing the devil population as it stands. Dr Hogg works in partnership with the Save the Tasmanian Devil Program, the Zoo and Aquarium Association Australasia and San Diego Zoo Global, to ensure that the insurance population is protected and can thrive, cancer free. “These devils are housed in a range of facilities ranging from intensive enclosures in zoos to fenced peninsulas in Tasmania and on Maria Island, off the east coast of Tasmania,” Dr Hogg says. So far, they are all disease-free.
“The challenge here,” says population geneticist Dr Catherine Grueber, a post-doctoral fellow in the group, “is ensuring that the captive populations don’t in-breed, which would cause a further lack of genetic diversity.”
But once again, a University researcher has found a unique solution to the problem.
A PhD student within the Australasian Wildlife Genomics Group, Rebecca Gooley, was working on DNA sequencing of some devil scat found in south-west Tasmania earlier this year when she found significant genetic differences between them and the DNA of other devils. Of the 17 genetic markers she screened for, nine were completely new variants.
“The discovery of the poo was an extremely exciting result,” says Gooley. “Finding a population that has a lot more diversity is really valuable for preventing in-breeding and provides an opportunity for us to introduce animals who aren’t related to each other for further breeding in insurance populations.”
While the Save the Tasmanian Devil Program team has begun to release healthy devils back into the wild population, this is still very much in its infancy.
Despite the promising advances of 2016 there is still a lot of work to be done to ensure the future of the Tasmanian Devil. This summer, an intrepid group of volunteers is in south-west Tasmania searching for more devil scat to test for further genetic diversity. This will allow the team to target areas for intense trapping in 2017. At the same time, Peel will begin to modify and manipulate the peptides to test their wider application – a reason for this beloved Australian animal tash a devilish grin.
The University recently ran a crowd-funding campaign to save the Tasmanian devil. To learn more or help advance this critical research, please contact Harkeet Puria on (02) 8627 8818 or email email@example.com.
Written by Lauren Sams (BA(Hons) ’07)