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A young Tasmanian devil. Tasmanian devils are threatened by devil 1 face tumor (DFT1), a transmissible cancer. Credit: Maximilian Stammnitz
Genomic analysis can aid efforts to save this endangered marsupial.
A transmissible cancer in the Tasmanian devil has evolved over the past two decades, with some lineages spreading and replacing others, according to a new study in the open access journal PLOS biology by Young Mi Kwon, Kevin Gori and Elizabeth Murchison of the University of Cambridge (UK) and colleagues. The evolutionary dynamics of cancer help explain how this Australian marsupial became endangered so quickly and could shed light on the evolution of other forms of cancer.
The Tasmanian devil is a carnivorous, small dog-sized marsupial found only in Tasmania, an island state off the south coast of eastern Australia. Devil 1 facial tumor (DFT1) was first observed in the mid-1990s and has since spread to devils across much of the island, transmitted from one animal to another through biting, a behavior common social. Surprisingly, cancer cells transferred in this way, instead of being eliminated by the new host’s immune system, survive and establish a new tumor. The infection is usually fatal.
Tasmanian Devil
To better understand the spread of the disease, the authors analyzed the genomes of 648 DFT1 tumors collected between 2003 and 2018. They found that early in the tumor spread, DFT1 split into five clades, or sub-ends. Two of these went extinct, while three continued to spread. One, clade A, has split once again. The authors mapped the distribution of each clade, which revealed how sick devils spread cancer across the environment; their findings support those of epidemiological research and underline the importance of geography in influencing the movements of demons and their disease.
The effects of human attempts to prevent spread were also reflected in the data: a pilot program to remove infected animals was likely responsible for a series of sub-cell replacements in an isolated region. The authors also identified several types of genomic instability in the DFT1 genome, including duplication and loss of genes and the gain or loss of entire chromosomes; they also described the frequency of genome-wide duplication leading to tetraploid tumors. However, the degree of genomic diversity within the devil tumor population was small compared to that often found even within a single human tumor, the authors noted.
Largely as a result of the spread of DFT1, and now exacerbated by the emergence of a second transmissible cancer, DFT2, the Tasmanian devil population has declined precipitously and the species is now endangered. “The results of this study may be useful for epidemiological modeling and prediction of the benefit of management intervention,” Murchison said.
Reference: “Evolution and lineage dynamics of a transmissible cancer in Tasmanian devils” by Kwon YM, Gori K, Park N, Potts N, Swift K, Wang J, et al., November 24, 2020, PLOS biology.
DOI: 10.1371 / journal.pbio.3000926
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