An international group of researchers has discovered that two regions in the genomes of Tasmanian devils (Sarcophilus harrisii) are changing in response to the spread of a recently emerged infectious disease.
Tasmanian devil (Sarcophilus harrisii). Image credit: J.J. Harrison / CC BY-SA 3.0.
The Tasmanian devil is found throughout the island state of Tasmania, Australia, although fossil evidence suggests that it once occupied much of the Australian mainland.
It is the largest carnivorous marsupial in the world, reaching 2.6 feet (80 cm) in length and weighing up to 31 pounds (14 kg).
This animal was given the unflattering ‘devil’ name by early settlers, perhaps after they heard the animal’s otherworldly cries in the night.
Tasmanian devils are nocturnal and usually solitary. They occupy several different dens, changing dens every 1-3 days, and traveling a mean nightly distance of 5.6 miles (9 km). However, individuals have occasionally been observed to move up to 31 miles (50 km) in a single night.
They are considered to be generalist predators and specialized scavengers. They actively hunt prey up to about 44 pounds (20 kg) in size using a combination of ambush and short, moderate-speed pursuits.
Prey comprise primarily medium- to large-sized mammals, although they will eat large invertebrates such as bogong moths and the carcasses of any dead vertebrates, leading them to focus on areas where lambing, calving or wallaby shooting are in progress.
Tasmanian devils display significant aggression toward one another, which often involves biting on the face.
This sometimes transmits Tasmanian devil facial tumor disease (DFTD), a nearly 100% fatal and transmissible cancer first detected in northeastern Tasmania in 1996.
DFTD has swept across nearly the entire species’ range, resulting in localized declines exceeding 90% and an overall species decline of more than 80% in less than twenty years.
Despite models that predicted extinction, populations of Tasmanian devils at long-diseased sites persist.
Washington State University’s Prof. Andrew Storfer, an evolutionary geneticist who has studied DFTD for nearly a decade, teamed up with colleagues in the United States, the United Kingdom and Australia to investigate whether there was a genetic component to some of the Tasmanian devils’ survival.
The team mined a vast trove of Tasmanian devil DNA collected and stored before and after the outbreak of DFTD by study co-author Dr. Menna Jones and her research group at the University of Tasmania.
The frequency of genes in specific regions of the old DNA were compared to the frequency of genes in corresponding regions of DNA collected following DFTD emergence at three sites on Tasmania.
The scientists identified two small genomic regions in the DNA samples from all three sites that exhibited significant changes in response to the strong selection imposed by the disease.
Five of seven genes in the two regions were related to cancer or immune function in other mammals, suggesting that Tasmanian devils are indeed evolving resistance to DFTD.
The researchers are in the process of determining the specific functionality of the genomic regions identified in the study.
They are hopeful that disease free devils with the apparently DFTD resistant DNA can be bred to enhance the genetic diversity of an off-island captive insurance population in case devil reintroductions are needed in the future.
“Our study suggests hope for the survival of the Tasmanian devil in the face of this devastating disease,” Prof. Storfer said.
“Ultimately, it may also help direct future research addressing important questions about the evolution of cancer transmissibility and what causes remission and reoccurrence in cancer and other diseases.”
The team’s findings were published this week in the journal Nature Communications.
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Brendan Epstein et al. 2016. Rapid evolutionary response to a transmissible cancer in Tasmanian devils. Nature Communications 7, article number: 12684; doi: 10.1038/ncomms12684
