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At long last... It's out! I'm so excited to share with you all my recent work on the phylodynamics of Devil Facial Tumor Disease (DFTD), now out in Science Mag! 1/n https://science.sciencemag.org/content/370/6522/eabb9772
What is DFTD? Well, it's a transmissible cancer! Put another way, DFTD is a transmissible cell line, having originated as a cancerous cell on a single devil. This cell line in trun is transmitted between individuals through common biting interactions. 2/n
Photo: David Hamilton
Photo: David Hamilton
First detected in Northeastern Tasmania, Australia, in 1996, DFTD impacts Tasmanian devils and is nearly universally fatal, and has swept across the island leading to species-wide declines of approximately 80%. 3/n
In turn, DFTD has led the devils to endangerment, and for about a decade we've thought that DFTD would ultimately drive them to extinction. Recently though, work has come out implying that perhaps rather than devil extinction, we should instead expect coexistence? 4/n
This is where our paper comes in. We wanted to characterize the epidemiological history of DFTD, from the time of its origination to the present day, with the aim of estimating its effective reproduction number (Re) at the present day. 5/n
At this point, some of you may be familiar with Re, given the whole pandemic thing. In short, Re describes the expected number of secondary infections each infected individual will generate in an already infected population. To do so, we looked to phylodynamic methods. 6/n
We managed to apply phylodynamic methods to a transmissible cancer! This is actually kind of wild - these approaches have historically been limited almost entirely to rapidy/measurably evolving pathogens like influenza, HIV, and morst recently Sars-Cov-2. 7/n
Using whole-genome sequences for 51 tumor samples, we screened more than 11,000 genes for a strong, clock-like signal and identified 28 that fit the bill. Now, what did we find? 8/n
We found that the disease probably originated well before its 1996 discover - likely in the mid-late 80's. DFTD then swept omnidirectionally across Tasmania, reaching a peak Re of ~3.5 in the mid 1990's coinciding with its discovery 9/n
However, the 'golden years' for DFTD appear to be a thing of the past! Re has plummeted towards the present day, and now hovers around 1. This means that each infected devil only replaces itself! These predictions of coexistence are looking more probable. 10/n
We find this pattern even when allowing for heterogeneity in rates of transmission across the tumor phylogeny. In all, it seems the rate of transmission of DFTD appears to be slowing. 11/n
What does this all mean? Well, this is a much needed dose of optimism and implies that perhaps extinction needn't be our expectation! That said, we still need to be cautious. 12/n
Photo: David Hamilton
Photo: David Hamilton
Devil populations may never fully recover - the slowed rates of transmission may be explained in part by reduced population densities. In short, our findings provide optimism for the fate of the devil, but emphasize the need for evolutionary motivated conservation efforts. 13/n
Beyond devils, this study paves a path towards the application of phylodynamics to much more slowly evolving pathogens, traditionally out of reach of this class of methods! 14/n
This is really exciting, both for the study of human and wildlife pathogens! I can't wait to see where this leads us! 15/n
I am deeply indebted to the help of all of my co-authors, including those on twitter and those that have not yet bitten the bullet! In no particular order,
@davidghamilton1 @MRuizAravena @cpkoza @comte_seb @TanjaStadler_CH @PHohenlohe
Photo: David Hamilton
@davidghamilton1 @MRuizAravena @cpkoza @comte_seb @TanjaStadler_CH @PHohenlohe
Photo: David Hamilton
If you can't get enough, there's also some press around this and related articles! https://www.sciencemag.org/news/2020/12/tasmanian-devils-claw-their-way-back-extinction
