In a previous post, I walked through a recent paper that was the first large scale genomic investigation of thylacines, talking about what we can learn from genetics, and how they went extinct on the mainland. All throughout this paper, parallels were drawn with one of the few remaining large marsupial predators of today: Tasmanian devils.
Tasmanian devils (Sarcophilus harrisii) are stockily built with raucous voices and a fierce disposition that suits their lifestyle of hunting and scavenging. Like thylacines, they once roamed the mainland. They began their path to extinction there due to the same factors of sudden, dramatic climate changes that shifted the landscape from a temperate, moist land to the hot, dry one we know today. Arrival of humans and dingoes to the mainland seemed to finish them off (1). However, they clung on - as they are want to do - in Tasmania, where not even irrational persecution could drive them out. Today they are facing daunting challenges. Foremost among them, a singularly brutal cancer.
Devil Facial Tumor Disease (DFTD) is a contagious cancer that spreads between devils through their saliva - unfortunately, devils mouth and bite each other a lot. Since it’s detection in 1996, it has spread rapidly, with devastating results: infected populations suffer heavy losses, with some declining by more than 90% in only two decades. The disease is unique to devils, and once the namesake tumors appear, the cancer becomes rapidly systemic and, ultimately, fatal. Due to the isolation of the species to Tasmania, the genetic diversity is already very low, limiting the species’ capacity to respond naturally to the disease.
Recently, we’ve made a few breakthroughs. In 2012, the entire Tasmanian devil genome was sequence. In doing so, the genes for the cancer were also identified and revealed two distinct types originating from one individual (2). Several captive populations have been established as insurance, both nationally and internationally. There have also been successful reintroduction of some captive reared devils back into the wild, on islands and even back on the Tasmanian mainland itself, a significant step in giving the species the best chance of surviving the DFTD epidemic (3). The Wild Devil Recovery project started in 2014, with aims to monitor and replenish wild populations whilst continuing monitoring of DFTD.
Excitingly, a 2016 study has found that some devils appear to be developing a genetic resistance to the cancer (4). Whilst not a complete resistance, it has great potential for helping devils survive this crisis by enabling captive populations to be selectively bred towards a more resistant genotype. The DFTD suppresses a devil’s immune system, leaving it unable to fight the infection; but the genes discovered by Epstein et al. are similar to those in other mammals that play roles in immune function and cellular communication. These genes may indicate that the devil’s immune systems are starting to develop ways to identify the cancer!
Even better, a subsequent study has demonstrated a small portion of wild devils seem to display these traits already (5). Though not strong enough to slow the spread, these are important steps forward. Last year, a study used this information to demonstrate that the cancer could be treated by taking the cancer and ‘turning on’ the genes that let the devil’s immune system recognize and fight it (6). Once injected, three of the five treated devils showed regression of their cancers, and they went on to live healthy lives. These discoveries may aid in the development of an effective immunotherapy treatment for infected individuals - in essence, allow the development of a kind of vaccine against this deadly disease.Â
With ongoing research, continued management of captive populations, reintroduction schemes, and mitigation of other threats like road strikes and habitat loss, there is hope for the devil yet!
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Brüniche-Olsen, Anna, Menna E. Jones, Jeremy J. Austin, Christopher P. Burridge, and Barbara R. Holland. "Extensive population decline in the Tasmanian devil predates European settlement and devil facial tumour disease." Biology letters 10, no. 11 (2014): 20140619.
Murchison, Elizabeth P., Ole B. Schulz-Trieglaff, Zemin Ning, Ludmil B. Alexandrov, Markus J. Bauer, Beiyuan Fu, Matthew Hims et al. "Genome sequencing and analysis of the Tasmanian devil and its transmissible cancer." Cell 148, no. 4 (2012): 780-791.
Tracy Rogers, Samantha Fox, David Pemberton, Phil Wise. "Sympathy for the devil: captive-management style did not influence survival, body-mass change or diet of Tasmanian devils 1 year after wild release." Wildlife Research 43, no.7(2015): 544-552.
Epstein, Brendan, Menna Jones, Rodrigo Hamede, Sarah Hendricks, Hamish McCallum, Elizabeth P. Murchison, Barbara Schönfeld, Cody Wiench, Paul Hohenlohe, and Andrew Storfer. "Rapid evolutionary response to a transmissible cancer in Tasmanian devils." NATURE 7, no. 12684 (2016): 1.
Pye, Ruth, Rodrigo Hamede, Hannah V. Siddle, Alison Caldwell, Graeme W. Knowles, Kate Swift, Alexandre Kreiss, Menna E. Jones, A. Bruce Lyons, and Gregory M. Woods. "Demonstration of immune responses against devil facial tumour disease in wild Tasmanian devils." Biology letters 12, no. 10 (2016): 20160553.
Tovar, Cesar, Ruth J. Pye, Alexandre Kreiss, Yuanyuan Cheng, Gabriella K. Brown, Jocelyn Darby, Roslyn C. Malley et al. "Regression of devil facial tumour disease following immunotherapy in immunised Tasmanian devils." Scientific Reports 7 (2017).
