September 7, 1936, was a sad day as Benjamin – the last confirmed Tasmanian tiger, or thylacine – died in captivity at Hobart’s Beaumaris Zoo. Now, these extinct stripey carnivorous marsupials may be getting a new lease of life. Scientists at the University of Melbourne, Australia have been provided a $3.6 million donation for the establishment of the aptly named Thylacine Integrated Genetic Restoration Research (TIGRR) Lab.
Around 3,000 years ago, thylacines once ranged throughout the Australian mainland but disappeared due to human hunting and competition from dingoes. Fortunately, a population became isolated in Tasmania. This protected them until early European settlers persecuted them as they were wrongly labeled as a “sheep killer”, and the government imposed a bounty of £1 per animal. This led to their extinction.
This direct human-influenced extinction is one of the most compelling cases for de-extinction. Other reasons include it being an apex predator important for stabilizing ecosystems – the habitat of Tasmania has also remained unchanged, so the thylacines could be re-introduced and enable reoccupation of its niche.
A project of this size will also develop the key technologies and resources that can help preserve and conserve surviving marsupial species that are currently endangered.
One issue that may arise is the genetic diversity of any successful population. Previous work showed limited genetic diversity within the population prior to extinction, but sequencing multiple individuals may help to recapture the genetic diversity in any future populations. Along with this, there have been previous examples of extreme bottlenecks not affecting repopulation. One is the Arabian oryx which went extinct in the wild in 1970s. A population of nine individuals in captivity helped grow the species to over 6,000 individuals – with 1,000 in the wild.
So how will these animals be brought back to life? In this case, knowledge is power.
Back in 2018, a team led by Professor Andrew Pask published the first genome sequence of a thylacine, using DNA from a pouch young specimen at Melbourne Museum stored in alcohol for the past 100 years. Previously, the draft assembly of the genome was incomplete. However, advances in DNA assembly and the explosion of high-quality reference genomes from related living species now allow new chromosome-scale genomes for the thylacine.
Now, the team is currently trying to improve the genome by sequencing many more specimens to determine the species variation and will compare this to the closely related dunnart marsupial – a mouse-sized animal with huge inky black eyes. This comparison will determine the quantity and scope of edits required to create a thylacine-like marsupial cell. This large computational project will also help bio-bank all ‘at-risk’ marsupial populations that are threatened or endangered.
When all of this information is gained, the “Jurassic-park-esque” experimentation will begin. Assisted reproductive technologies (ART) will be developed to use living stem cells to make an embryo, by fusing a "thylacine" cell with an empty dunnart egg. This egg will then be transferred into the host mother’s uterus.
Now, there is a size difference between the dunnart and the thylacine – but luckily, marsupials give birth to tiny young regardless of the adult size, and typically the babies will complete development in the pouch while sucking milk from the mother. When the thylacine baby is born, it will be isolated at birth and hand-reared or fostered by a marsupial.
Overall, this type of project is likely to receive critics and the public may link it to a very popular movie franchise. But as Pask told the Washington Post: “When people say, ‘Didn’t we learn anything from Jurassic Park?’ — well, it’s very different bringing back a velociraptor to a thylacine.”