The Thylacine: An Exemplary Candidate for De-Extinction

BY Sara Ord

Synopsis:

A carnivorous marsupial native to the Australian mainland, New Guinea and Tasmania, the last known thylacine died in captivity in 1936 in a Tasmanian zoo. An ecosystem engineer with a central role in preserving the biodiversity and health of its native ecosystem, bringing back the thylacine would help rebalance a rewilded Tasmania.

Inside This Article:

  • What is unique about the thylacine, and why did it go extinct?
  • How will thylacine de-extinction benefit species, ecosystems, and the scientific enterprise?
  • Can the thylacine be de-extincted? If so, how?

The Thylacine: A Quirky Evolutionary History

Dogs don’t have pouches. Neither, certainly, do they have kangaroo tails or zebra stripes.

Or do they?

The thylacine, commonly known as the Tasmanian tiger or wolf, is one such evolutionary wonder which, as a marsupial under strong selective pressures, ended up looking just like that: a dog – with a pouch, rigid tail, and stripes.

First appearing in the fossil record about 4 million years ago, evolving from mainland Australia and parts of New Guinea, it travelled to Tasmania when there remained a land bridge connecting it to the mainland.

As a marsupial by ancestry, the thylacine naturally carries up to four young ones in its pouch – think kangaroos, koala bears, wombats, and possums. Living and hunting in packs however, it swiftly evolved a long snout with pointy canines, scissor-like molars, and raised heels (giving the thylacine its unique toe-walk) for greater speed as an ambush predator. Its jaws opened up to 80 degrees while offering a strong hunting-friendly biting force (1). Rigid, its tail offered balance when reared up on its hind legs.

Despite sharing a closer common ancestor with kangaroos than dogs or even wolves however, the evolution of these characteristics are a textbook case of adaptive convergent evolution with canids (2) – reflecting the remarkable emergence of similar phenotypes in response to environmental natural selection (3–5). A mere 2 feet tall, weighing in at 45 pounds, the Thylacinus cynocephalus has been quite literally named according to its evolutionarily quirky resulting appearance as a “pouched animal with the shape of a dog”.

The Spiritual Value of the Timeless Thylacine and its Tragic Extinction

A unique species with a fascinating evolutionary history, the thylacine had been central to spirituality among the Australian aborigines (6). Images of thylacines adorn their thousand-year old caves, as some tribes revered them – even going as far as to build a small protective hut over a buried thylacine’s bones for fear of spiritual retribution otherwise (7).

But, when Asian seafarers brought dingoes to mainland Australia 4,000 years ago, these tended to outcompete thylacines – being larger and stronger, reproducing more swiftly, and hunting more efficiently. Climate change in the form of drought placed additional pressure on them (8), and hunting by indigenous peoples led to the tipping point precipitating their demise across mainland Australia (9).

In Tasmania, their future was no rosier.

The thylacine was in direct competition with the quoll and Tasmanian devil for the same food sources – exacerbated by acute pressures resulting from its isolated island environment conducive to low, fragile population genetic diversity (10) .

Despite surviving into the 1900’s, the thylacine was then heavily prosecuted as a result of preying on famers’ sheep – on which the Tasmanian economy almost entirely depended on. A bounty was introduced in 1888 – 1 pound for an adult and 10 shillings for a pup – and upwards of 3,000 animals were killed in the early 1900’s. The last known thylacine, Benjamin, died in 1936. Ironically, Benjamin was the only thylacine to have received full legal protection, two months prior, given the ostensible threat to his species – tragically too late. The day of Benjamin’s death is, now, recognized as National Threatened Species day.

Pragmatic De-Extinction: A 5-point Case for the Thylacine

  1. A moral decency
    Tantalizingly close to our collective memory, tragically ingrained in recent Australian history, the thylacine remains a symbol of an entire ecosystem, region, era, the de-extinction of which is not only a tribute to its long-lost appreciation, but a moral imperative – righting an anthropogenically induced wrong in the context of the devastating 6th extinction within in which we are tragically enmeshed (11). A disruptive conservation solution channeling our shifting global consciousness.
  1. A boost to robust biodiversity
    Apex predators such as the thylacine play a critical role in the predator-prey relationships that shape and balance their ecosystems. Ideally while maintaining a healthy balance with competitors, they do so by eliminating animals below them in the food chain. These include invasive species – by far the greatest threat to biodiversity in Tasmania – including mesopredators (roughly in the middle of the food chain). Top-down control of these will help thrive native mammals, birds, reptiles, and amphibians – in a manner not unlike the mesopredator control resulting from the reintroduction of the Tasmanian devil to mainland Australia (12,13). Predated species naturally, also, include the weak and the sick, and, diseased animals having otherwise been more easily eradicated by thylacines, the loss of the thylacine was likely to have precipitated the emergence of Tasmanian Devil facial tumor disease.
  1. Ecosystem restoration
    Until recently, large apex animals at the top of the food chain were ubiquitous across the globe (having been for millions of years) – migrating humans destroyed a large chunk of them, however, generating destructive cascading effects across terrestrial and marine ecosystems worldwide. One of the most destructive results is known as trophic downgrading: a fundamental weakening of an ecosystem which a key species had played a crucial role in maintaining (14). Apex predators kill off herbivores, reducing grazing pressures, and ensuring the maintenance of vegetation structures critical to healthy ecosystems. Wolf reintroduction to Yellowstone, for example, has restored tree communities, thereby boosting biodiversity and populations of key ecosystem engineers such as beavers (15). Reduced grazing pressures also increase plant carbon fixation – as such enhancing climate change-clamping carbon sequestration (16). Such a mechanism means that wolf reintroduction to the North American boreal forest could be, according to Yale ecologist Oswald Schmitz, “on the same order of magnitude as the fossil fuel emissions of 6–20 million passenger cars per year” (17). Reintroducing extirpated apex predators to their native homelands – such as the thylacine to Tasmania – fundamentally reestablishes important ecosystem dynamics.
  1. Rewilding Australia
    The latest report from IUCN’s Red List places Australia as the 5th country most affected by extinctions and the 6th country with the greatest number of endangered species. Rewilding is a cornerstone strategy for a healthy, thriving Earth – and, hand in hand with strong biodiversity and a healthy ecosystem, reintroducing the thylacine to its native habitat will set the stage for a robust and thriving rewilded Australia.
  1. A scalable, elegant endeavor with multidimensional ramifications
    The scientific enterprise inherent to de-extincting the thylacine will generate novel, scalable data and knowledge – inevitably deepening our genomic understanding of the thylacine and its relatives, galvanizing the development of gene editing technologies, and setting a stage ripe for successful species conservation work in the future. In so doing,  developed technologies will have ripple effects across a slew of other species, including Australia’s extant marsupials, which have been increasingly threatened by Australia’s bushfires. Not only will marsupial stem cell biobanks be developed in order to preserve these amazing species in their most diverse forms, but some species will be specifically targeted for genetic enhancement. These include, but are not limited to, the norther quoll, which is further endangered because it preys on lethally toxic invasive cane toads: CRISPR gene editing technologies honed during the process of thylacine de-extinction will allow for the engineering of cane toad toxin-resistant quolls.

A Simple Recipe for Genetic Regenesis

Thylacine de-extinction will be carried out according to 9 almost simple steps. The thylacine’s full genome has already been sequenced in unprecedented detail (18,19). In brief, CRISPR genetic engineering will then be used to integrate core thylacine traits into the genome of a host species closely related to the thylacine. The resultant genetic material will be used to generate a thylacine embryo to be implemented into a surrogate mother from a closely related species.

The Thylacine: An Exemplary  Candidate for De-Extinction

Recreating individual species to preserve the web of life, the anthropogenic de-extinction of key species is quintessential Life 3.0 in action (20) – life tweaking its own architecture for strategic recursive self-improvement. To this end, the thylacine in particular, having gone extinct relatively recently from a habitat which remains fundamentally unaltered, is the ideal candidate for de-extinction. Today, emblem of native species loss across Australia, the least the thylacine deserves is to regain its spot in a rewilded version of the ecosystem we were primarily responsible for extirpating it from – coming full circle.

 

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