(CN) — For the last decade, it appeared a contagious facial cancer would lead to the extinction of the Tasmanian devil, but new research suggests otherwise.
An unprecedented genetic analysis of the fatal devil facial tumor disease published in Science on Wednesday suggests not only that the marsupials are co-evolving with the disease, but that they may very well survive into the next century.
“Collectively, our group has a number of studies that have shown devils are evolving in response to the disease and the disease seems to be transitioning toward an endemic pathogen,” said Andrew Storfer, study author and biology professor at Washington State University. An expert in host-pathogen evolution, Storfer said became interested in the Tasmanian devil disease by chance while on sabbatical in Australia.
Discovered in 1996, devil facial tumor disease is a contagious cancer transmitted among Tasmanian devils through social biting. It is 100% fatal, killing hosts within 6 to 12 months. Since the disease emerged 25 years ago, it has decimated the devil population by 90%. Most expected the cancer to drive the rare mammals into extinction.
Instead, the analysis of 11,359 genes from 51 tumor samples collected between 2003 and 2018 reveals an intricate picture of co-evolution and adaptation. Phylodynamics — the study of how immune systems and evolution shape diseases — also helped scientists understand the genetic lineages of the Ebola virus and the novel coronavirus SARS-CoV-2, which causes Covid-19. Until now, phylodynamics was limited to studying simple viruses.
“One of our challenges was screening over 11,000 genes for evolution in a clocklike or regular pattern, which helps us generate an evolutionary tree that we can then use to estimate parameters like the growth in the population and the transmission rate over time,” Storfer said. “It took several months to do that, but the good news is now anyone can use that approach, in theory, to look at pathogens with larger genomes like bacteria and fungi.”
This analysis revealed 28 genes mutations following a clocklike pattern, allowing researchers to date the disease origination to between 1977 and 1987. In addition to identifying two different versions of the disease, researchers found both strains spread evenly and rapidly throughout the devils’ range.
Most surprising of all, this study provides evidence that rather than the death of the Tasmanian devils, the disease is becoming endemic to their life. The rate of infection appears to be decreasing, from each infected animal spreading the disease to 3.5 others down to a 1:1 infection rate.
More research is needed to confirm how devils have adapted to the disease, but two theories prevail: immunological adaptations, meaning the devils have become better at fighting the disease, and behavior.
In fact, research from the same lab published in the Proceedings of the Royal Society B on Tuesday suggests sick devils have started to self-isolate, thus reducing the spread of the disease.
“Ecological models show that under most scenarios, the devil should survive for at least 50 to 100 years,” Storfer said with cautious optimism. “This suggests that perhaps the best management strategy is actually just to let evolution run its course in the wild.”
The research was funded by a grant from the U.S. National Institutes of Health and by the Australian Research Council.
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