The year of the (Tasmanian) tiger

With 2022 being the Year of the Tiger according to the Chinese zodiac, it is appropriate that research efforts over the past 12 months have shone a light on the Australian thylacine, also known as the Tasmanian tiger. In some cases this was a literal light, with ABC journalists discovering that thylacine fur glows under black (UV) light — a trait shared with other Australian animals such as the platypus, bilby and wombat. Yet this focus on the thylacine is rather remarkable given that the apex predator has been extinct for close to a century — although some researchers are doing their utmost to change that.

The thylacine in the cupboard

The thylacine, a unique marsupial carnivore, was once widespread in Australia but was confined to Tasmania by the time Europeans arrived in the 18th century. It was soon hunted to extinction by colonists, with the last known animal, made famous through photographs and film footage, dying at Hobart’s Beaumaris Zoo in 1936. But it was recently found that this particular thylacine was in fact outlived by an older female, captured by trapper Elias Churchill and sold to the zoo in May 1936.

“The sale was not recorded or publicised by the zoo because, at the time, ground-based snaring was illegal and Churchill could have been fined,” said Robert Paddle, a comparative psychologist from the Australian Catholic University.

When the female died — with no one realising it was the last known thylacine in captivity — its body was transferred to the Tasmanian Museum and Art Gallery (TMAG). But with no record of thylacine material from 1936 ever filed or found in the museum’s zoological collection, it was assumed that the body had been discarded. It was only the detection of an unpublished museum taxidermist’s report dated 1936/37, mentioning a thylacine among the list of specimens worked on during the year, which led to a review of all the thylacine skins and skeletons in the TMAG collection — and the subsequent discovery of the missing specimen in a cupboard in the museum’s education department.

It turned out that the body had been prepared by the taxidermist not as a research specimen — which is why it wasn’t recorded – but as an education specimen. “The thylacine body had been skinned, and the disarticulated skeleton was positioned on a series of five cards to be included in the [museum’s] newly formed education collection,” explained Kathryn Medlock, Honorary Curator of Vertebrate Zoology at TMAG. Indeed, the skin and skeleton were included in an educational program that travelled from school to school, teaching students about the anatomy of Tasmanian marsupials, until they were eventually stored away in the 1980s — all without anyone knowing the significance of what they had been handling.

Paddle and Medlock’s paper on their discovery will soon be available to view in the journal Australian Zoologist, while the last thylacine’s skin and skeleton — still attached to the five cards created for the education collection — are now on display at TMAG for any curious visitors to see. But if evolutionary biologist Professor Andrew Pask has his way, it won’t be the last thylacine for long…

Skull of the last thylacine that died at Beaumaris Zoo on 7 September 1936. Collection: Tasmanian Museum and Art Gallery.

Resurrection of the thylacine

The idea of bringing the thylacine back from extinction is ambitious, to say the least, but what would be the benefit? According to some researchers, resurrecting the species has the potential to rebalance the Tasmanian and broader Australian ecosystems, which have suffered biodiversity loss and ecosystem degradation ever since the animal went extinct. The apex predator played a critical role in regulating the ecosystem by hunting non-native mesopredators, which prey on native herbivores — so rewilding the thylacine to select areas could help return them to their natural state, as has been the case with the reintroduction of wolves to Yellowstone National Park, for example.

Back in March, The University of Melbourne received a $5 million philanthropic gift to establish a world-class research lab for de-extinction and marsupial conservation science, aptly named the Thylacine Integrated Genetic Restoration Research (TIGRR) Lab. Helmed by Pask, the lab would develop technologies that could achieve de-extinction of the thylacine and provide crucial tools for threatened species conservation.

Pask and his team had already succeeded in sequencing the thylacine genome, having previously extracted DNA from the soft tissue of a 108-year-old, alcohol-preserved thylacine pouch young specimen from Museums Victoria. With the genome providing “a complete blueprint on how to essentially build a thylacine”, according to Pask, the philanthropic donation allowed the TIGRR team to move forward, improving their understanding of the thylacine genome and comparing it to that of the thylacine’s closest living relatives — such as the fat-tailed dunnart or ‘marsupial mouse’ — in the hope of using CRISPR gene-editing technology to make the latter genome more closely resemble the former. Indeed, the researchers have already figured out how to reprogram dunnart skin cells into stem cells, which they hope to use to create a gene-edited living embryo.

Thylacine pouch young specimens. Collection: Tasmanian Museum and Art Gallery.

A colossal partnership

Some months after receiving the donation, it was announced that the TIGRR Lab was being joined in its quest by Colossal Biosciences, a Texas-based genetic engineering and de-extinction company that had previously announced its own plans to de-extinct the woolly mammoth and restore the species to the Arctic tundra. The collaboration saw Pask join Colossal’s scientific advisory board, bringing a wealth of knowledge to the company around marsupial gestation and evolution.

Pask said at the time that the partnership was the most significant contribution to marsupial conservation research in Australia to date, unlocking access to a consortium of scientists and resources for the thylacine de-extinction effort. It would see Colossal’s resources and expertise in CRISPR gene editing paired with TIGGR’s genome sequencing and identification of marsupials such as the dunnart to provide living cells and a template genome, to be edited to recreate a thylacine genome.

“A lot of the challenges with our efforts can be overcome by an army of scientists working on the same problems simultaneously, conducting and collaborating on the many experiments to accelerate discoveries,” Pask said. “With this partnership, we will now have the army we need to make this happen.”

The TIGGR Lab is also looking to establish reproductive technologies tailored to Australian marsupials, as the successful birth of the thylacine requires the advancement of current marsupial assisted reproductive technology. Pask said the TIGRR Lab has been pursuing growing marsupials from conception to birth in a test tube without a surrogate — which is conceivable given infant marsupials’ short gestation period and their small size — and that the team is close to producing the first lab-created embryos from Australian marsupial sperm and eggs.

According to Pask, the partnership is set to accelerate de-extinction efforts to the extent that the first living baby thylacine could be a reality in as little as 10 years’ time. Furthermore, the partnership is expected to produce technology and knowledge to influence the next generation of Australia’s marsupial conservation efforts and combat increasing extinction events.

“Our efforts to protect the endangered northern quoll — long threatened by the invasive cane toad native to South and Central America — will also be aided by this partnership, as we could produce northern quolls with a slight genome-edit making them resistant to cane toads,” Pask said.

“While our ultimate goal is to bring back the thylacine, we will immediately apply our advances to conservation science, particularly our work with stem cells, gene editing and surrogacy, to assist with breeding programs to prevent other marsupials from suffering the same fate as the Tassie tiger.

“This is a landmark moment for marsupial research and we’re proud to team up with Colossal to make this dream a reality.”

Top image credit: iStock.com/Vac1

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