CLONING A THYLACINE will be more challenging than Church’s project to resurrect the mammoth using the Asian elephant. Their ancestors diverged just six million years ago, and they share about 99% of their genes. There is no equivalent species for the thylacine.
Pask suggests Western Australia’s numbat, whose genome he plans to sequence, might provide the best starting DNA blueprint. It is one of the thylacine’s closest living relatives, last sharing a common ancestor 30 million years ago. The diminutive termite-eating creature has stripes, but that’s where the similarity ends. Adult numbats are slightly bigger than a squirrel, whereas adult thylacines weighed about 30 kg. Despite this, Pask says as much as 95% of their DNA may be identical.
That still leaves an awful lot of numbat DNA to edit, making it an expensive proposition. But, as with all other genetic technologies, the costs are likely to fall fast. Pask will wait and watch while other de-extinction projects, particularly that of the mammoth and a similarly advanced effort to resurrect the passenger pigeon of North America, perfect the technologies.
The next series of steps are the most unpredictable: cloning an embryo, implanting it into a surrogate and gestating the pouch young.
Getting cloning to work is a major challenge. The techniques used to create Dolly are notoriously difficult to apply to different species. It was only in 2017 – more than 21 years after Dolly – that it was successfully replicated in a primate, with Chinese scientists producing two genetically identical longtailed macaques.
Once researchers get a thylacine-recoded numbat egg to start developing into an embryo, gestating it is also far from straightforward. For humans and sheep, both placental mammals, the science of implanting embryos into a womb is well-established. Not so for marsupials, where implantation takes place much later. In placentals we know how to prime a mother with hormones to accept an embryo, but this knowledge is completely lacking in marsupials.
To master assisted reproduction in marsupials, Pask has turned to a different thylacine relative, the tiny mouse-like dunnart. They breed well in captivity and produce a litter of up to 20 young twice a year. Nevertheless, he says, “it will be a decade before we get a really good handle on a lot of this stuff in marsupials”.
Pregnancy is also a very different proposition to placental mammals. A marsupial still looks something like a foetus when it is born, typically two weeks after conception. About the size and shape of a pink jellybean, it must crawl up its mother’s abdomen and into her pouch, where it latches onto a teat to suckle. Its mother’s milk, like a placenta, changes its composition to guide most of the joey’s development.
This two-stage gestation does offer intriguing possibilities. A thylacine embryo might be gestated in the uterus of a smaller marsupial, and then transferred to the pouch of a larger one – perhaps a kangaroo. Cross-fostering is a well-established technique to help bolster the populations of endangered rock wallabies. In 2014 a rock wallaby successfully fostered a baby tree kangaroo in its pouch.
Another option is hand rearing, already widely employed for rescued kangaroos and also for Tasmanian devils captive bred to save the species from the devil facial tumour disease (DFTD) that has decimated wild populations.
ONCE A THYLACINE joey has weaned, at about nine months, there would be a new set of hurdles. Would it behave like a thylacine?
Little is known about natural behaviours, such as hunting or mating, as the thylacine was scarcely observed in the wild. “Many behaviours are innate,” Pask says, “but there would be a large subset that they probably learnt from individuals around them. Learned behaviour is more common in species that use complex decision-making to hunt prey, and preserved thylacine brains reveal a well-developed frontal cortex, indicating good memory and capacity to learn.”
We do know thylacines did not fare well in captivity. The Royal Zoological Society of NSW noted in 1939: “The thylacine does not take kindly to captivity, and rarely lives under such conditions for any length of time.” From 1850 to 1931, 224 were kept at zoos in cities including Washington DC, New York, Berlin and Paris. London Zoo had 20 over the years. Some died during journeys, others stopped eating and fell ill. None bred. While our skill at keeping animals has increased enormously, there is no guarantee resurrected thylacines would do better.
Understanding how a species might fare is important, says Beth Shapiro, an evolutionary biologist at the University of California, Santa Cruz, and author of How to Clone a Mammoth: The Science of De-extinction (2015). “Populations living in captivity, possibly for decades, need not only to survive but must also learn how to live,” she says. “They need to learn how to feed and protect themselves, how to interact with others, how to avoid predation, how to choose a mate, and how to provide parental care.”
You also need a population with genetic variety, Shapiro says. Pask suggests it might be possible to edit such variation into the genome. “If you can get over the hurdle of making all those millions of edits
to the genome to make it look like a thylacine in the first place,” he says, then introducing variability into immune system genes “is nothing”.
IF ALL THESE HURDLES can be overcome, the end goal of any de-extinction effort surely must be to reintroduce animals to the wild. One potential issue for some de-extinction candidates – appropriate habitat – is not a problem. Reserves cover about half of Tasmania today. “The habitat is the same, the animals they ate are still there,” says Archer. “There’s no question it could be put back into the bush of Tasmania.” There is also good reason to do so: “The thylacine was Tasmania’s key carnivore. Getting it back is about restabilising ecosystems currently under threat.”
That still may not be enough to convince everyone we should bring back thylacines. Many argue deextinction projects take the focus away from the vital work to save other species from extinction.
“If you have the millions of dollars it would take to resurrect a species and choose to do that, you are making an ethical decision to bring one species back and let several others go extinct,” Canadian conservation biologist Joseph Bennett has said. “It would be one step forward, and three to eight steps back.”
Yet what is true today may not be true tomorrow. Pask agrees that, right now, resources should go to saving endangered marsupials. “If, however, in 10 to 15 years’ time it becomes relatively inexpensive, then I think it is definitely worth pursuing.” Having hunted the thylacine to extinction, he says, “we owe it to the species to bring it back”.
It may not be entirely thylacine, but one day, a century or so from now, a creature that looks and behaves like one might be found quietly slipping between piles of rusty rocks that bear its likeness, etched millennia ago.
For millions of years, Thylacines roamed across Australia and Papua New Guinea. A drying climate led to the loss of forest habitat and wiped out most thylacine populations on the mainland around 3,000 years ago. The island of Tasmania remained the last refuge. Though thylacines looked much like dogs, they last shared an ancestor with canines about 160 million years ago. The resemblance is an example of convergent evolution, in which animals develop similar features to fill similar ecological niches. Thylacines were marsupials, carrying their young in a pouch on their bellies like other iconic native Australian animals including koalas and kangaroos.
A few tweaks to turn a numbat into a thylacine? The striped termite- eating numbat, about the size of a large squirrel, will have its DNA edited to resemble that of its long-lost cousin.
IMAGES 01 Nick Rains / Australian Geographic 02 Tasmanian Museum and Art Gallery 03 Rod Start / Museums Victoria 04 Andrew Pask 05 Vac1 / Getty Images 06 Craigrjd / Getty Images