Cambridge researchers have challenged a previous study which found that a facial cancer that has devastated the Tasmanian devil population is on the decline.
Devil facial tumor disease, a deadly cancer spread by biting and sharing food, first emerged in the 1980s. The spread of DFTD led to the species being listed as endangered by the International Union for Conservation of Nature in 2008.
The original study, published in the journal Science in 2020, found that the rate of transmission had slowed so that an infected animal would only infect one other animal – previously an infected devil would infect another 3.5.
The researchers were “cautiously optimistic” that the devils had developed a natural immune response to the cancer and concluded that the disease no longer a threat to the survival of the species.
Cambridge scientists repeated the study and concluded that key findings from the original study could not be replicated, leaving the future of Tasmanian devils uncertain, in a critique published in Royal Society Open Science.
Elizabeth Murchison, a professor of comparative oncology and genetics at the University of Cambridge and one of the review’s senior authors, said the original researchers sequenced DNA half the recommended number of times.
She said it was recommended that scientists sequence DNA at least 30 times when analyzing tumors to have confidence that a variant is actually a mutation. Her reanalysis found the researchers in the original study sequenced DNA an average of 15 times.
Murchinson said the mutation rate recorded by the original researchers was “incredibly high” and suggested that the mutations recorded were probably non-sense.
The authors of the initial study disagreed and said they stand by their research. They said that in the years since then they have published papers that “support the basic conclusion that continued survival of Tasmanian devils in the wild is likely and that there has been rapid evolution of devils in response to the disease”.
In a joint statement, they said the Cambridge researchers had previously approached the journal Science to publish a critique of the first study, but the publication rejected it. They said that Murchison and her co-authors had now published “an almost identical” critique in Royal Society Open Science and had not been granted the right to respond before publication, contrary to the “usual procedure”.
The Cambridge researchers said they replicated the initial study after noticing that the tree depicting how the tumor evolved over time generated by the original researchers “looked nothing like their own tree”.
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Carolyn Hogg, a population biologist at the University of Sydney who was not involved in either study, praised the depth of sequence analysis the Cambridge researchers took. She said they are “by far the world experts” in the field.
She disagreed with the conclusions drawn by the authors in their initial paper, and did not see how their conclusions were supported by their data.
“I don’t know if the [initial] researchers did anything wrong,” she said. “They probably weren’t aware [of sequencing depths] … because they are not cancer researchers.
“It’s a cautionary tale for scientists to be careful about the conclusions they draw if they’re not an expert.”
Hogg said the “best bet” for Tasmanian devils was a vaccine being developed by the Menzies Institute for Medical Research.
