Good news for Tasmanian Devils: They Are Becoming Resistant to Species-Ending Infectious Cancer
Michael Byrne reports in Motherboard:
There are good reasons that transmissible cancer isn’t really a thing. This mostly has to do with the immune systems of advanced organisms—while our own cancer evades immune responses by virtue of being, well, part of us, cancer from other individuals is recognized as an invader. Thus, outside cancer is quickly rooted out and eliminated. Cases of transmissible cancer in humans are extreme novelties, occurring rarely in immunocompromised patients, such as those with HIV.
In nature, a few species are unlucky enough to have infectious cancer as an everyday threat. Shellfish get it thanks to weak immune systems and an existence based on the constant ingestion and filtering of seawater shared by other shellfish. Dogs get itthanks to the swapping of tissues that occurs in rough dog sex. Tasmanian devils get it because of the tissue swapping involved in constantly fucking up each other’s faces. That’s a prerequisite for transmissible cancer occurring at all: the transmission of full-on tissue. A cancer cell doesn’t behave like a bacterium or virus—cancer needs to be transplanted en masse for it to gain footing elsewhere.
In most cases, devil facial tumour disease (DFTD) is fatal. Over the past two decades, some 80 percent of the entire Tasmanian devil population has been decimated by the cancer. The disease has spread across nearly 95 percent of the island of Tasmania and has affected all known devil populations. Epidemiological models have predictedthat DFTD likely portends the end of the entire Tasmanian devil species.
There may be hope, however. No, the devils don’t seem to be learning to interact socially without destroying each other’s faces, but their immune systems are learning to fight back against the infection via phenomenally rapid adaptations. This is according to a paper published on Tuesday in Nature Communications by disease ecologist Andrew Storfer and colleagues at Washington State University.
“Overall, our results reflect a rapid evolutionary response to this strong selection imposed by DFTD, and such a response to a highly lethal, novel pathogen has rarely, if ever been documented in wild populations,” Storfer and co. write. “The only other well-studied example, the evolution of rabbit resistance to myxomatosis following its release in Australia, took place over a much larger number of host generations.”
The swapping of tissues is a necessary but not sufficient condition for transmitting cancer. There is still the issue of immune responses. . .
This is, quite literally, evolution in action.