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To What Extent Do We Understand DFTD, and What Are the Conservation Options for Tasmanian Devils?

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To What Extent Do We Understand DFTD, and What Are the Conservation Options for Tasmanian Devils? To what extent do we understand DFTD, and what are the conservation options for Tasmanian Devils? ABIGAIL SHEPPARD CANDIDATE NUMBER: 8972, CENTRE NUMBER: 58625 Table of Contents Abstract ................................................................................................................................................... 3 Glossary ................................................................................................................................................... 3 Introduction ............................................................................................................................................ 5 Literature Review .................................................................................................................................. 6 History of the Tasmanian Devil .......................................................................................................................... 6 What is DFTD? ................................................................................................................................................... 9 Allograft Theories of Transmission ................................................................................................................... 14 Immune Response to DFTD ........................................................................................................................... 16 Genetic Diversity and the MHC .................................................................................................................... 18 Non-Allograft Theory of Transmission ............................................................................................................. 22 DFTD Evolution ................................................................................................................................................ 23 Tasmanian devil conservation ........................................................................................................................... 25 Discussion .............................................................................................................................................. 25 Which is the stronger theory: The Allograft or Non-Allograft Theory? ........................................................... 26 What are the conservation options for Tasmanian devils? ................................................................................ 27 Captive breeding ............................................................................................................................................ 27 Vaccine development ..................................................................................................................................... 28 Disease suppression through culling ............................................................................................................. 29 Depopulation, Translocation and Population Reinforcement ....................................................................... 30 Fencing .......................................................................................................................................................... 31 Issues with management options: .................................................................................................................. 32 Conclusion ............................................................................................................................................. 32 Evaluation ............................................................................................................................................. 34 2 Abstract Devil Facial Tumour Disease (DFTD) is an emergent transmissible cancer exclusive to Tasmanian devils (Sarcophilus harrisii) which is threatening the species with extinction in the wild. Research began ten years ago (Pye, 2016)7, when nothing was known about the tumour and little was known about Tasmanian devils. The research since then has covered the cause and pathogenesis of DFTD, the immune response of the devils, the immune evasion mechanisms of the tumour, the transmission patterns of DFTD, and the impacts of DFTD on the ecosystem. I have collated this information and put it into the context of conservation strategies designed to mitigate the impacts of DFTD on Tasmanian devils and the Tasmanian ecosystem, and I have also evaluated how much is really known about DFTD. Glossary 2-microglobulin (B2ml): a protein that stabilises the heavy chain of MHC I molecules. Allograft: transplant of biological tissue from one individual to another of the same species. Chromosome painting: a technique in which chromosome-specific probes, labelled with colour fluorescent dyes, are hybridised with a cellular karyotype to identify individual chromosomes of a cell and the rearrangement of nom-homologous fragments that occurs by end-joining DNA repair mechanisms. Demethylation: a decrease in methylation patterns, resulting in a genome that may be hypo-methylated. Hayflick limit: the number of times a cell population can divide before telomeres shorten to a critical length and cell division ceases. Immunohistochemical testing: the process of selectively imaging antigens (e.g. proteins) in cells of a tissue by exploiting the principle of antibodies binding specifically to antigens. Karyotype: the arrangement of chromosomal material in a cell. Rearrangements, deletions, duplications and other chromosomal mutations may be observed by examining the karyotype. Kinship: the genetic relationship, either based on a known pedigree or molecular data, between one animal and another. 3 Major histocompatibility complex (MHC): a set of molecules primarily involved in the presentation of antigenic peptides to the immune system; first discovered for their role in graft rejection. Methyl-CpG binding domain: enzymes that cause active demethylation. Methylation: an epigenetic modification of DNA that may lead to changes in gene expression. Microsatellite: (short tandem repeats) regions of highly repetitive DNA (usually two to five base pairs in length), widely used for many ecological genetics applications, such as diversity surveys, quantifying population differentiation or percentage analysis. miRNA: small non-coding RNA molecules that regulate gene expression. Myelin basic protein (MBP): a protein encoding a gene that is expressed in Schwann cells and an indicator that DFTD originally arose in this tissue. Natural Killer (NK) cells: cytotoxic lymphocytes of the innate immune system that can kills cells lacking cell surface MHC. Reverse transcriptase-polymerase chain reaction (RT-PCR): laboratory technique for studying gene expression through generating complementary DNA transcripts from RNA. Schwann cell: cell of the peripheral nervous system; progenitor of DFTD. Sex-determining region (SRY): a gene found on the Y chromosome that is involved in mammalian sex determination. Single nucleotide polymorphism (SNP): a sequence variant that occurs as a substitution in the alignment of two or more sequences of bases. 4 Introduction In July 2017, I shadowed a Biological Sciences PhD student at Southampton University. She was in the process of finding peptide candidates for a vaccine against a “transmissible cancer” called DFTD, or Devil Facial Tumour Disease. I was allowed to help her run PCRs and gel electrophoreses on Tasmanian devil genes, which I really enjoyed. At the time, I had only vaguely heard of such a thing as a cancer that can be passed between individuals, so the concept was incredibly thought-provoking to me, and I decided to research it further. This resulted in me completing an EPQ on the topic, as I believe the implications of understanding such a devastating disease can help further cancer research and our methods of saving endangered species. The Tasmanian devil (Sarcophilus harrisii) is the largest living marsupial, belonging to the Dasyuridae family. Listed as Endangered on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List, the global Tasmanian devil population has declined by more than 60% in the last ten years (IUCN, 2017)1. Research indicates that an invariably fatal infectious cancer called Devil Facial Tumour Disease (DFTD) 1 The International Union for Conservation of Nature is the global authority on the status of the natural world and the measures needed to safeguard it. It is an extremely reputable source and it is classed as an official source of information regarding species and their conservation status. It gives a comprehensive review of the conservation levels and threats to thousands of species and it often referenced by top researchers and governments. It is also used to make official decisions about the conservation efforts for endangered species by governmental bodies and non- 5 is responsible for the decline. DFTD currently occurs across the majority of the geographic range of the Tasmanian devil and continues to spread at variable rates, within the range of 7 to 50km per year, depending on the location (McCallum, 2007)2. Mark-recapture data from the most intensively studied population at the Freycinet National Park in Tasmania, estimated a decline in total population size of 30% in the 3 years after the disease first arose, with an annual decline in the adult (two years and above) population of 50% (Lachlish, 2007)3. Research on the nature of DFTD only began fairly recently, and there is still much to understand about it. The priority now
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