The extinct Tasmanian Tiger
Source: By Aneesa PA: The Indian Express
Scientists in the US and Australia have embarked on a $15-million project to resurrect the thylacine or Tasmanian tiger a marsupial that went extinct in the 1930s, using gene-editing technology. The ambitious project aims to reintroduce the animal to its native place Tasmania to revive the region’s lost ecological balance.
Interestingly, this is not the first attempt to revive thylacines. In 1999, an Australian scientist, Dr Michael Archer, embarked on an unsuccessful journey to resurrect the animal using cloning technology from a perfectly preserved specimen in a museum.
So, what are Tasmanian Tigers and how did they become extinct?
Tasmanian Tiger (Thylacinus cynocephalus), the only animal in the Thylacinidae family to survive in modern times, was a marsupial mammal that raises young ones in a pouch.
Even though the species earned its nickname Tasmanian Tiger because of the stripes along its back, it was a slow-paced carnivorous that usually hunted alone or in pairs at night. The sharply clawed animal had a dog-like head and ate kangaroos, other marsupials, small rodents, and birds.
Once widespread in the grass and woodlands of continental Australia extending north to New Guinea and south to Tasmania, the animal’s fate changed after the European Colonisation of Australia.
The animals were reported to have eaten poultry of farmers, and were killed following official authorisation. In 1830, Van Diemens Land Company announced a bounty on the animal. Years later in 1888, the Tasmanian Parliament itself passed an official bounty of 1 pound on thylacines.
A series of photographs by naturalist Harry Burrel published in the 1920s showcasing thylacines catching poultry and other birds also explains the unpopularity of this animal among the public, even though the authenticity of these pictures was questioned later.
Apart from this, competition with another animal, the Dingo, is also considered a reason for its extinction.
The last wild thylacine was killed between 1910 and 1920. Following this, the Australian government declared the thylacine a protected species in July 1936. But two months after the announcement, Benjamin, the last captive animal, died at the Beaumaris Zoo in Hobart. The official declaration of the animal’s extinction was in the 1980s.
The animal was at the top of the food chain, and hence played a significant role in balancing the ecosystem of its habitat by removing the weak animals and maintaining species diversity. Also known as the apex predator for the same reason, its disappearance from the food chain resulted in Trophic Downgrading — causal degradation of an ecosystem that occurs when higher trophic level animals are removed from the food chain, resulting in loss or exponential growth of other species.
Trophic Downgrading also results in disruption of biogeochemical cycles, wildfires, growth of invasive species, and carbon sequestration, among other effects.
As the thylacine was the only apex predator in its ecosystem, its absence impacted the Tasmanian Devil, which was almost wiped out by a facial tumour disease. The thylacine would have prevented this by removing sick and weak animals from the ecosystem, which would have eventually controlled the spread of the transmissible diseases.
The resurrection process
Even though the last living thylacine died over 86 years ago, many embryos and young specimens of the species have been preserved.
For the de-extinction project, the scientists led by Dr. Andrew Pask, a professor of Epigenetics Biosciences at the University of Melbourne, will be using a genome sequenced from a DNA extracted from a 108-year-old specimen held at Australia’s Victoria Museum.
This genome will be compared with the closest living animal of the species– the fat tailed dunnart — to identify all the differences. Once all the differences are identified, scientists will engineer the living cell’s DNA where it is different, essentially engineering the extinct species back.
“Once we have the engineered cells, we use stem cell technologies and cloning techniques to turn those cells back into a living animal. While all of these technologies already exist, this is the first time they will be developed for marsupials,” Pask told Indianexpress.com.
The fat-tailed dunnart is a mouse-like species in the Dasyuridae family in Australia. With an average body length of 2.4–3.5 inches, they are one of the smallest carnivorous marsupials.
According to the Colossal, de-extinction will not be complete until the success of the rewilding process – reintroducing the animal to its native habitat — which will ‘stabilise the fragile ecosystem of Tasmania.’
“The thylacine is a great candidate for de-extinction because it only went extinct in 1936 due to human hunting and the ecosystem we are looking to return it to is still intact. Furthermore, we have incredible tissue samples and genomes assembled as well as many additional pelts that are being sequenced for population genomics studies,” Ben Lamm, CEO and co-founder of Colossal said.
Even though the team hasn’t set a timeline for the project, it is expected to take much less time than the de-extinction of Woolly Mammoth, considering the gestation of elephants is longer than Dunnarts.
Lamm said the process of the rewilding project needs to be carefully studied, and executed in collaboration with local governments, conservation groups, rewilding experts, ecologists, and indigenous people groups.
“We have started conversations with leading rewilding and conservation groups in Australia and Alaska as well as consultants that work with the local indigenous people groups in both Australia and the broader Arctic circle,” he said.
However, amid praises, many scientists have also raised concerns about the practicality of the technology.
“De-extinction is a fairytale science,” Associate Professor Jeremy Austin from the Australian Centre for Ancient DNA told The Sydney Morning Herald.
“It’s pretty clear to people like me that thylacine or mammoth de-extinction is more about media attention for the scientists and less about doing serious science,” he said.
De-extinction technology; possibilities and challenges
De-extinction, or resurrection biology, is the method of creating a species that went extinct or is endangered, in order to revitalise ecological diversity and balance shattered due to reasons ranging from biodiversity loss to climate change. While cloning is the most widely used method of de-extinction, genome editing and selective breeding are also considered effective ways.
The Pyrenean ibex, a subspecies of Spanish ibex, was one of the first extinct animals that have been resurrected using somatic cell nuclear transfer (SCNT), even though the baby Ibex died minutes after its birth from lung defect.
Apart from Colossal’s project to resuscitate Woolly Mammoths and thylacines, a cooperation between the Dutch Foundation partnered with multiple universities, called Tauros Programme, is currently working to breed a cattle species similar to the extinct wild ancestor of domestic cattle, aurochs.
Other candidates for de-extinction are Maclear’s rat, an extinct large rat species endemic to Christmas Island in the Indian Ocean, the passenger pigeon, a type of migratory bird in North America, and the quagga, which is a subspecies of plains zebra.
One of the challenges of de-extinction is that reintroducing the species to its former habitat may make it an invasive species, which will also impact the balance of the current ecological system.
