By Georgina Hockings
The Tasmanian devil is a carnivorous marsupial that, in the wild, is found exclusively in Tasmania. The population is being attacked by a cancer by the name of Devil Facial Tumour Disease (DFTD). This has decimated the wild population and as yet no cure has been found. Stephan Schuster and his colleagues have sequenced the genomes of two devils. This is the first time this has happened and has shown that there is low genetic diversity throughout the population. This could have resulted from the much reduced population size because of the cancer; however, Schuster has shown that, there was low genetic diversity in the population before the cancer emerged.
DFTD is believed to have emerged in a single female 16 years ago and is an unusual form of cancer as it is the cells themselves which are infectious. The cancer is passed on through one animal biting another such as in a fight or during breeding. Unfortunately once a devil has contracted the cancer it is almost always fatal and has led to a 60% population crash. Studies predict that the Tasmanian devil will be extinct in decades if nothing is done to try and save them.
Parks and Wildlife Services Tasmania. (2011)
The two animals used in the study by Schuster were from the greatest geographical gap possible. One was from the North-West while the other from the South-East. This was done to ensure that the differences in the genomes were a reasonable marker for the diversity within the entire population. The study found that there were only 914,827 differences in the two genomes. In comparison, the number of differences between the genomes of a southern African Bushman and a Japanese individual is 4,800,466. These differences are when there is a difference in the base pairs or nucleotides of the DNA. For example if a section of one animal’s DNA is ATGC GTCA and the same section of the other animal is ATGC TGCA then there is a single difference in the nucleotides. While this low genetic diversity is being heightened by the cancer there is evidence through analysis of 14 complete mitochondrial genomes from current and museum specimens that there was low genetic diversity in the population 100 years ago.
The devil’s low genetic diversity has led to the cancer being passed from animal to animal without prompting an immune response says Katherine Belov of the University of Sydney. The minimal difference in the genomes means the devil’s immune system cannot tell that the cancerous cells are not regular tissue and therefore should be eradicated.
The Department of Primary Industries, Parks, Water and Environment. (2011).
There is hope for the devils though. Sequencing the genomes of these two animals has given scientist invaluable information and could lead to structured breeding programs designed to increase the genetic diversity of the captive population and ensure that any genetic information in the wild population is not lost. This study by Stephan Schuster is evidence that genotyping is becoming a vital tool in the conservation of endangered species.
The Department of Primary Industries, Parks, Water and Environment. (2011). Tasmanian Devil Facial Tumour Disease – FAQs (online) http://www.tassiedevil.com.au/tasdevil.nsf/TheDisease/BD2717C762779EE8CA2576F1001D0110
Parks and Wildlife Services Tasmania. (2011). Tasmanian Devil – Sarcophilus harrisii (online) www.parks.tas.gov.au/index.aspx?base=387
Coghlan, A. (2012). Immortal’ Tasmanian devil brings vaccine hope (online). www.newscientist.com/article/dn21489-immortal-tasmanian-devil-brings-vaccine-hope.html [Accessed 10 March 2012].
Schuster, S. et al. (2011), ‘Genetic diversity and population structure of the endangered marsupial Sarcophilus harrisii (Tasmanian devil)’, Proceedings of the National Academy of Sciences of the United States of America. 108.30, pp. 12348- 12353. (online). www.pnas.org.ezproxy.library.uq.edu.au/content/108/30/12348.full.pdf+html[Accessed 10 March 2012]