Signs shown of genetic resistance to DFTD

Research by an international team of scientists, published at the end of August in the journal Nature Communications, shows two regions in the genomes of Tasmanian devils (Sarcophilus harrisii) appear to be evolving in response to the fatal facial tumour disease that has ravaged populations in the wild for almost 20 years.

Evolutionary geneticist Andrew Storfer from Washington State University, and geneticist Paul Hohenlohe from the University of Idaho, compared tissue samples collected from Tasmanian devils by Menna Jones over a 17-year period. An Associate Professor and wildlife ecologist at the University of Tasmania, Jones is credited with first identifying DFTD during the mid-1990s, and she subsequently established long-term field sites to study the animals. In less than 20 years populations of devils in the wild have declined by more than 80 per cent.

Jones, who is a co-author of the paper, said two small genomic regions were identified in the recently collected DNA samples from three sites: Narawntapu in Tasmania’s north-east, West Pencil Pine in western Tasmania’s Cradle Valley, and Freycinet, on the east coast. They all exhibited significant changes in response to the strong selection imposed by the disease. Continue reading Signs shown of genetic resistance to DFTD

New research on devils’ decline

It was curiosity about the reasons for Tasmanian devils’ low genetic diversity, a characteristic that was often noted but never fully explained in many of the papers she was reading, that prompted University of Tasmania PhD candidate Anna Brüniche-Olsen to discover why. The results of her study, the first to provide a ‘quantitative assessment of devil population size changes through time’ were published recently in Biology Letters.

Brüniche-Olsen and her team analysed available microsatellite data from 10 different locations across Tasmania to estimate the stability of devil populations over time, and they found evidence of declines that pre-date the fatal facial tumour disease that is currently ravaging the devils’ wild populations.

The results show four major events are likely to have influenced the current population distribution and low genetic diversity of Tasmanian devils. Environmental change around the last glacial maximum approximately 20,000 years ago was responsible for the first decline. Continue reading New research on devils’ decline

Federal funding denied for devil program

In the lead-up to the federal election the former federal government announced it would not provide $4 million in funding for a project submitted under the Caring for Country program by the Save The Tasmanian Devil Program. The Devil Island Project would have enabled the relocation of Tasmanian devils from insurance populations, that are free of the fatal facial fungal disease decimating the species in the wild, to be safely enclosed behind a 4.8km fence across the Freycinet Peninsula on Tasmania’s east coast. Similar plans are being prepared for a 40km barricade in the state’s north-west.

While he refused to commit to funding the project if the Coalition won government, federal environment minister Greg Hunt instead said his intention would be to work with Zoos Victoria and the Tasmanian government on a Tassie devil recovery program, and to: “work to preserve, protect and help the population of Tassie devils recover.” Continue reading Federal funding denied for devil program

Reduced effect of Tasmanian devil facial tumour disease at the disease front

Pathogen-driven declines in animal populations are increasingly regarded as a major conservation issue. The Tasmanian devil (Sarcophilus harrisii) is threatened with extinction by devil facial tumor disease, a unique transmissible cancer.

The disease is transmitted through direct transfer of tumor cells, which is possible because the genetic diversity of Tasmanian devils is low, particularly in the major histocompatibility complex genes of the immune system.

The far northwest of Tasmania now holds the last remaining disease-free wild devil populations. The recent discovery of unique major histocompatibility complex genotypes in the northwestern region of Tasmania has raised the possibility that some animals may be resilient to the disease. The authors examined the differences in the epidemiology and population effects of devil facial tumor disease at 3 well-studied affected sites in eastern Tasmania and 1 in western Tasmania (West Pencil Pine). Continue reading Reduced effect of Tasmanian devil facial tumour disease at the disease front

Transmissible cancers in dogs and Tasmanian devils

Figure 1.

The Tasmanian devil, the world’s largest marsupial carnivore, is facing possible extinction in the wild due to a transmissible facial cancer known as Tasmanian devil facial tumour disease (DFTD) (Figure 1). DFTD is spread when living cancer cells are spread between animals by biting. In DFTD, the living cancer cell itself is the infectious agent of disease and it remains unclear why these cancer cells are not detected and rejected by the devil’s immune system. The distressing plight of the Tasmanian devil has drawn attention to the existence of transmissible cancers, parasitic cancers spread by the transfer of living cancer cells between hosts. However, it remains a surprisingly little-known fact that the only other transmissible cancer that bears any resemblance to DFTD is a dog cancer that is right under our noses here in Australia.

Canine transmissible venereal tumour (CTVT) is one of the world’s most remarkable cancers. It is a transmissible cancer that affects dogs worldwide. Usually spread during coitus, the disease is most prevalent in areas with large numbers of free-roaming sexually active dogs. The tumour affects both male and female animals, and appears to affect dogs of any breed. CTVT generally manifests itself in the appearance of tumours in and around the genital area, often at the base of the penis in males and in the vulva of females. Starting as small shiny pink/grey lesions, the tumours can progress to become very large and multi-lobulated (Figure 2). The tumour may aggressively invade surrounding tissues and become ulcerated and secondarily infected. However, a combination of surgical debulking and chemotherapy (using vincristine) is often curative.

Figure 2

Genetic studies have provided strong evidence that CTVT is in fact one living cancer cell line that has spread worldwide with dogs. Thus all CTVT tumours are derived from a single original tumour that arose once and has been transmitted through the dog population as a clone. The tumour itself bears closest genetic resemblance to wolves, suggesting that this tumour may have first arisen in a wolf before hitch-hiking its way into dogs through sexual contact. Genetic evidence suggests that the tumour may in fact be quite old, and that the original wolf that gave rise to the tumour may have even lived thousands of years ago. CTVT is by far the oldest known continuously growing cancer in the world. Continue reading Transmissible cancers in dogs and Tasmanian devils