Protecting the Tasmanian devil from extinction
An international team of researchers has developed a model to predict whether keeping an individual Tasmanian devil in captivity would help preserve enough genetic diversity for the species to survive the onslaught of the deadly cancer ripping through its habitat. This innovative approach began when the team, made up of scientists from Australia, Denmark and the United States, looked at whole-genome analyses of two Tasmanian devils - one that had died of a contagious cancer known as Devil Facial Tumour Disease (DFTD) and one healthy animal. This model, set out in the team's study published in the Proceedings of the National Academy of Sciences (PNAS), will contribute to efforts being made to prevent the extinction of the much-loved Tasmanian devil, a marsupial found in the wild exclusively in the Australian island-state of Tasmania. If the model proves successful, it could eventually be used to help prevent the extinction of other endangered species. The species is under severe threat from DFTD, which was first observed on the east coast of Tasmania just 15 years ago. Since then it has spread rapidly westward, threatening the entire species with extinction. The thinking behind the approach is that if a number of healthy Tasmanian devils were kept in zoos or 'protective custody' until the tumour ran its course, then the captive animals could be released back into their former habitat and the population could begin to grow anew. DFTD is an atypical cancer, disfiguring the victim and causing death from starvation or suffocation within months. 'The disease is like nothing we know in humans or in virtually any other animal. It acts like a virus but it actually is spread by a whole cancerous cell that arose in one individual several decades ago,' explains Stephan Schuster, one of the study's authors from Penn State University in the United States. 'This malignant cell is transferred directly from one individual to another through biting, mating, or even touching. Just imagine a human cancer that spread through a handshake. It would eradicate our species very quickly.' Yet efforts to preserve the species must be based on strict genetic considerations, as Webb Miller, the study's lead author explains. 'It's not just a matter of scooping up a few individuals at random and locking them away. Our team developed a smarter, more calculated approach: We asked ourselves, which individuals would be the best candidates for "protective custody", and what criteria would we use to make those determinations? We soon realised that the answer was to compile genetic data and to analyse it in novel ways.' The team approached this extinction dilemma from two angles. The first was to sequence the complete genomes - 3.2 billion base pairs each - of 1 individual Tasmanian devil of each sex. Cedric, as the male was called, had a natural resistance to two strains of DFTD, but succumbed after being infected with a different strain of the disease last year. The female, called Spirit, had contracted the vicious cancer in the wild. The scientists also sequenced the genome of one of Spirit's tumours. As Cedric and Spirit came from the extreme north-west and south-east regions of Tasmania respectively, they represented the maximal geographic spread of the species. This meant the team had a measure to use as an approximation of genetic diversity. After analysing the genomic data from the two animals, and of the genetic characteristics of the tumour, the team created a model that could determine which individual animals should be selected for captive breeding programmes. 'It might seem you'd want to choose only those individuals that are genetically resistant to the DFTD cancer. However, that would defeat the purpose of maintaining genetic diversity because, by definition, you'd be selecting a tiny subset of the gene pool,' comments Schuster. 'Instead, our model suggests a more balanced approach. You don't want to put out just the one fire - the cancer. Instead, you want to develop a pool of diverse, healthy individuals that can fight future maladies or even pathogens that have not yet evolved.'For more information, please visit:Penn State University:http://www.psu.edu/
Countries
Australia, Denmark, United States