Although transmissible cancers occur very rarely in the animal kingdom, Tasmanian devils are susceptible to two fatal such diseases, known as “devil facial tumor 1” (DFT1) and “devil facial tumor 2” (DFT2). Both of these diseases manifest with disfiguring facial tumors and have caused rapid population declines in recent decades. Now, a research team led by the University of Cambridge has mapped the emergence and mutations of these cancers and characterized their ongoing evolution, highlighting the continued threat they pose to Tasmanian devils.
“The incredible fact that Tasmanian devils have not one, but two, transmissible cancers, makes it possible to compare their evolution, and this gives us new insights into the key mechanisms involved,” said senior author Elizabeth Murchison, a professor of Comparative Oncology and Genetics at Cambridge.
“By looking at the mutations that have accumulated in these cancers’ DNA, we can trace the origins and evolution of these diseases. Our results show that the two cancers arose through similar processes and that both have striking signals of ongoing evolution. It is difficult to predict how this continued cancer evolution will impact devils.”
By creating a map of the entire genome of the Tasmanian devil – known as a “reference genome” – and comparing it to DNA collected from 119 cancer tumors, the experts identified mutations in the tumors and used these findings to build “family trees” of how the two cancers emerged and evolved.
The analyses revealed that DFT2, which was first identified in 2014 and remains confined to a small area of southeastern Tasmania, acquired mutations three times faster than DFT1, which was first observed in 1996 and since then spread through the entire country. These findings suggest that DFT2 is a faster growing cancer than DFT1.
“DFT2 is still not widespread in the devil population, and very little is known about it. We were really startled to see just how quickly it was mutating, alerting us to what could be a very unpredictable threat to the devils in the long term,” said lead author Maximilian Stammnitz, a postdoctoral fellow at the Center for Genomic Regulation in Barcelona, who conducted this research during his doctoral studies at Cambridge.
Moreover, Stammnitz and his colleagues discovered that DFT1 arose in the 1980s, about 14 years before it was first detected, while DFT2 emerged between 2009 and 2012, shortly before it was first observed. By mapping the mutations DFT1 underwent, the researchers estimated an explosive transmission event soon after it emerged, involving a single Tasmanian devil infecting at least six other conspecifics. In addition, they identified for the first time an instance of DFT1 transmission between a mother and the offspring in her pouch, and found that the incubation period can in some cases be longer than a year – two findings which may have crucial implications for conservation scientists struggling to protect this species.
“Transmissible cancers pose an unprecedented and unpredictable threat to Tasmanian devils. This research highlights the continuing importance of monitoring and conservation programs. It also gives us new insights into the evolutionary mechanisms operating in cancer more broadly, including in human cancers,” Murchison concluded.
The study is published in the journal Science.
By Andrei Ionescu, Earth.com Staff Writer
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