The hunt for the thylacine, Australia’s elusive Tasmanian tiger
Image credit: Diomedia, Getty Images, Dreamstime
How modern science is busting myths about the extinct marsupial predator, the Tasmanian tiger.
The Tasmanian tiger wasn’t actually a tiger, despite its stripes. Nor was it a dog. The ‘thylacine’ – a derivative from the scientific name Thylacinus cynocephalus – was officially declared extinct in 1982, and its last known specimen died in captivity in Hobart Zoo in 1936.
Neuroscientist Professor Kenneth Ashwell of the University of New South Wales School of Medical Sciences, thinks the thylacine became extinct on the Australian mainland because it couldn’t compete with the dingo. The dingo never crossed the Bass Strait into Tasmania, but in its absence, European settlers hunted the thylacine to near extinction. The ‘tiger’ was thought to be taking sheep and a bounty was placed on its head.
According to paleontologist Professor Mike Archer of the University of New South Wales’ School of Biological, Earth and Enviromental Sciences, in reality, feral dogs were mostly the culprits, as the thylacine’s preferred prey was “chihuahua-sized” wallabies. Modern science, namely a study led by behavioural ecologist Marie Attard, has since shown that its jaw was probably too weak to grapple with large prey.
Archer recalls when he first thought of cloning the thylacine. It was an embarrassing moment, he says, for it was still “pre-Dolly the sheep” and his colleagues’ reaction was laughter.
Between 1999 and 2003, Archer was director of the Australian Museum, which had a specimen collection including a thylacine joey in a jar. “The 18th-century anatomists were wonderfully meticulous, they preserved the young and the adults,” he says. Nobody knows why it was preserved in ethanol instead of being skinned and dried, as was the custom at the time, but it was serendipitous, for this preserved its DNA. Although there was also a lot of human DNA contamination from handling, the tooth cells were protected by a hard matrix, which bacteria couldn’t get at.
Archer describes Australia’s unique flora and fauna as the other side of the mirror. It was after discovering evidence of giant wombats in New South Wales’ Wellington Caves that Darwin realised the evolution of animals could change in place, says Archerl. “If you’re a discovery junkie, Australia has masses of undiscovered things.
Despite being declared extinct, sightings of the ‘Tassie tiger’ both on the Australian mainland and in Tasmania are in the high hundreds. Wildlife biologist and conservationist Nick Mooney says that most sightings in Tasmania are in the west, north-west, and central highlands, although with no central data collection it is difficult to specify. Mooney is often involved in trying to verify sightings. However, he agrees that there is still no hard proof – though he is hopeful that the shy and nocturnal thylacine may still exist.
According to Mooney, a thylacine detective needs trail cameras, aka camera traps – a standard survey method for most wildlife. “I know people who have up to 50 in the bush all sending them [SMS picture] messages. They have revolutionised searching. People are also starting to use sophisticated auditory recording methods – some gear now will search for particular sounds programmed in. Unfortunately, we have no recording of a thylacine for such programming.”
Meanwhile, the thylacine’s fellow marsupial, the Tasmanian devil, has managed not just to survive but also to thrive in Tasmania, where it numbers many thousands. It was not big enough to be scary to people, says Mooney, and was never branded a ‘tiger’.
Mooney does not believe in cloning the thylacine, saying he can’t see the clones being released into the wild anyway.
Over in New Zealand, in his University of Otago lab, geneticist Neil Gemmell is preparing to travel to Scotland to extract environmental DNA from Loch Ness, the home of the assumed Loch Ness monster, in the hope that this search for traces of the elusive Nessie could be replicated on dry land in Tasmania to discover whether the thylacine is extinct or not.
Gemmell and an international team are going to identify species in Loch Ness, including a possible monster of the deep. Gemmell will take water samples at three different depths and the DNA will be sequenced.
Environmental DNA (eDNA) is tiny fragments from skin, scales, feathers, fur, faeces, urine and saliva, which can be matched with DNA databases. It is a kind of DNA profiling, but not quite like Scotland Yard’s. “Our focus is on assessing the composition of species in an environment, while forensics is generally focused on evaluating differences among individuals”, says Gemmell.
He describes the “relatively simple process” of the DNA extraction: “Water samples are filtered... to retain all the free cells present in the sample. We then extract the DNA from that material using pretty standard approaches – which generally involve lysis with a detergent, the breakdown of proteins with enzymes, and the extraction of the DNA using a series of solvents. Once extracted, the DNA is precipitated using ethanol and resuspended in a buffer that protects it from further breakdown.”
Gemmell agrees that possibly, in a terrestial setting, eDNA could be used to look for thylacine evidence, too. Meanwhile, dead thylacines are still yielding discoveries. “MRI and diffusion tensor imaging are opening up some exciting possibilities for studying brain connections in rare and endangered animals,” says brain evolution expert Professor Ashwell.
He is collaborating with Professor Gregory Berns, a neuroscientist from Emory University’s School of Medicine in Atlanta, who explains: “Post-mortem brains are usually preserved in a mixture of formalin and alcohol. MRI has the ability to detect differences between grey matter (the neurons and synapses) and the white matter (the axons – connections between the neurons).
Diffusion tensor imaging (DTI) goes a step further and measures how water molecules move along the axons. [From this], we can reconstruct a rough map of the internal wiring diagram of the brain called the connectome. Then, we compare how these diagrams differ between species.”The scans showed that the thylacine predator brain had a bit more frontal cortex compared to the Tasmanian devil brain. This could demonstrate more decision-making and planning when looking for lunch.
However, “it is fair to say that executive planning in the thylacine is not as sophisticated as in a canid”, says Professor Ashwell, “because the area of cortex devoted to that function (frontal association) is smaller in the thylacine”. One intriguing possibility, notes Berns, is that because marsupial gestation occurs largely in the pouch, this might have an effect on how the brain develops – a placenta will be much more metabolically efficient for a developing animal than when consuming nutrients through milk.Dr Christy Hipsley, research associate at Museums Victoria, has done a different type of thylacine scanning.
This evolutionary biologist/vertebrate paleontologist says museum curators don’t tend to like researchers cutting up their specimens, so Hipsley used a CT scanner to make 3D digital models.She says that while scanning is limited when it comes to examining soft tissue, “computer models are being generated that also allow integration of soft tissue information with CT scans, for example to estimate strains and stresses on the skeleton related to known muscle orientation”. This method proved extremely valuable for reconstructing the biomechanical properties of extinct animals.
In 2016, Hipsley gave a talk at the University of Melbourne. It was there that Associate Professor Andrew Pask from the University of Melbourne’s School of BioSciences asked her to compare the thylacine skull with that of wolves and foxes.
“In medical CT scans, or CAT scans, the person lies still while the X-ray tube moves around the body taking radiographs,” explains Hipsley. “The CT scanners we use look different in that the X-ray source is still while the object rotates 360 degrees between the tube and detector. The process afterwards is essentially the same: the series of single X-rays are combined into a volume that can be visualised in three dimensions and digitally ‘dissected’.”
What they discovered was that this marsupial carnivore had adapted long limbs to capture prey. But as a marsupial pup (not a cub), the thylacine had started out the other way around. In Hipsley’s words, they were often born very prematurely and had to crawl from the birth canal into the mother’s pouch where they attached to a teat and continued their growth. This meant that their forelimbs were already highly developed at the time of birth compared to their hindlimbs. “We found that about a month before leaving the pouch their proportions reverse and the hindlimbs grow rapidly to overtake the length of the forelimbs,” Hipsley adds.
Associate Professor Pask thinks this is the most amazing example of convergent mammal evolution (when two different animals grow to look the same): “We are now asking ourselves when two animals evolve to look very similar, as the thylacine and wolf did, do their genomes also reflect this similarity – i.e. can we see similar changes in the DNA code in both species that drive the evolution of their similar body shapes?”
Pask then followed on from Archer in sequencing the thylacine genome. According to him, previous attempts to sequence the genome had been hampered by the quality of the DNA contained in the museum specimens. DNA breaks down over time into many small bits, and most of the museum specimens (which are bones and skin) have only tiny bits of DNA – the fact that prevented previous attempts to sequence and then build the genome.
“We found one sample from Museums Victoria which had unusually intact DNA, so we were able to get sufficient sized pieces of the genome,” he explains. “We used standard methods, the same as those used to sequence human genomes, to generate the data and then build the genome using supercomputers.”
Pask says the “de-extinction angle” is still a long way off, but their work to define which regions of the genome are driving evolution of the thylacine will ultimately assist this goal.
This would not be the first example of cross-species cloning. Professor Archer says the Tasmanian devil could be a possible host egg donor, whose own DNA has been inactivated. He mentions somatic cell nuclear transfer (SCNT), which brought Dolly the sheep to life. The nucleus, whole or reconstructed, from thylacine cells, however, would be injected into the devil’s unfertilised, nucleus-inactivated egg cell. A tiny electric shock would then cause the nucleus to begin to operate as part of the new hybrid cell, after which it would be implanted into its surrogate devil mother’s uterus.
Alternatively, Archer suggests, CRISPR could be used to change the genome in the egg nucleus of the devil so that it matches the DNA sequence determined for thylacines. Or else, given rapidly advancing technology, it should soon be possible to directly synthesise new thylacine chromosomes de nova rather than have to alter the DNA of the chromosomes of another species.
Where does this rapid advance of technology leave evolution? Such speed will surely have unforeseen impacts on the natural world? Archer believes that cloning is already standard in agriculture and being risk-averse would still have “kept humans in caves whacking stones”. He says that, contrary to what ecologists hoped for, habitat preservation is failing spectacularly. “We can’t turn our back on other strategies such as the Frozen Ark, which freezes endangered species’ DNA,” he concludes.
Archer does suggest another option though – keeping native animals as pets. If a thylacine and not a terrier had been on the end of our leads, would the Tasmanian tiger still be alive today?
The Thylacine Museum online at www.naturalworlds.org/thylacine/index.htm contains a database of thylacine specimens as well as information about ‘Benjamin’, the last Tasmanian tiger.
UK wildcat sightings
A giant wildcat – one of the biggest ever recorded in the world – was spotted in March. Nicknamed the Clashindarroch Beast, the animal was captured on camera near the city of Aberdeen in Scotland.
The creature, which is estimated to be 1.2m from nose to tail, was spotted as part of the Scottish wildcat conservation project operating across the Highlands.
But sightings of large exotic cats in the UK are not uncommon.
There were 127 recorded sightings of anomalous big cats (ABCs) in Yorkshire alone between April 2004 and July 2005, but most of the reports were not very reliable.
In 1980 a puma was captured in Inverness-shire, Scotland. The capture followed several years of sightings in the area of a big cat matching the description of the one captured, which had led local farmer Ted Noble to erect a cage trap. The puma was subsequently put into the Highland Wildlife Park zoo and given the name ‘Felicity’. When she died she was stuffed and placed in Inverness Museum.
In 1989 a jungle cat that had been hit by a car was found on the roadside in Shropshire.