A new study offers hope for the survival of Tasmanian devils, whose numbers have been decimated in recent years by a highly contagious form of cancer.
But a population of devils in an affected area in western Tasmania is stable and healthy. A study describing these survivors and speculating how they are managing to avoid the scourge was published in the October 6 issue of Conservation Biology.
Devil facial tumor disease (DFTD) was first noticed by an amateur photographer in 1996. Infected devils develop lesions and lumps around their mouths that turn into cancerous tumors that can spread to the entire body. The tumors grow rapidly and uncontrollably, impeding the animals' ability to eat. In 15 years, the population of wild Tasmanian devils, which are found nowhere else, has declined 70 percent.
DFTD is one of a few known cancers that are contagious. The cancer cells themselves act as infective agents, spread from devil to devil via bites, the sharing of food, and aggressive mating. Devils may be especially vulnerable to DFTD because of the low diversity in their immune genes, especially in the major histocompatibility complex genes. The cancerous tumors have the same genes, so Tasmanian devil immune systems have trouble recognizing the tumor cells as foreign.
Recently, a population of devils in the northwest corner of Tasmania, called West Pencil Pine, has been the focus of much study. Biologists identified a genetically distinct group there with unique major histocompatibility complex genes. The new study reports that in West Pencil Pine, the devil population looks much like it did four years ago, when observations began. The number of devils contracting DFTD is much lower than in other regions and the population does not seem to be declining.
The authors of the study suggest two possible explanations: a difference in the West Pencil Pine devils' immune systems, or a difference in the strain of DFTD infecting them. Research is ongoing to determine if either or both of these explanations are correct, but the possibility that this population of devils is uniquely immune offers a ray of hope for the entire species. If some devils are naturally resistant to DFTD, efforts could be made to spread their genes and repopulate areas of Tasmania where devil populations have suffered. A breed and release program with the offspring of West Pencil Pine survivors may create a more genetically diverse -- and healthier -- wild population.