Brain structure of Tasmanian tiger revealed
VERY LITTLE IS known about the behaviour of the Tasmanian tiger. Although animals were kept in captivity at zoos in both Hobart and London, few systematic studies were performed and most of the data we have are based on anecdotal reports from bushmen, farmers and hunters.
The thylacine was once common across Australia. It vanished from the mainland several thousand years ago, but persisted in Tasmania until the early 20th century. A government bounty scheme for hunters from 1830–1914 finally drove it extinct there.
Most reports say the last thylacine died in captivity in Hobart Zoo in 1936, but it may have survived in the wild until the 1940s.
With such few data from living animals, scientists have turned to the anatomy of museum specimens to make educated guesses about its behaviour. Though the thylacine had a stronger bite force than the dingo, the anatomy of its head and neck may have meant it was less suited to taking large prey.
Its elbow joint suggests it was more of an ambush than pursuit predator, and an analysis of its teeth hints it was a ‘pounce-pursuit’ predator that took prey in the 1–5kg range.
3D reconstructions of the white matter tracts – nerve fibres are coloured according to their approximate orientation (left-right = red, rostral-caudal = green, dorsal-ventral = blue). (Credit: Gregory Berns)
Thylacine’s complex predatory niche
In an attempt to understand more about what it was capable of, researchers have now scanned two century-old thylacine brains – one kept at the Smithsonian Institution in Washington DC and the other at the Australian Museum in Sydney. Four brains are known from museum collections, but two were in such poor condition they were not useful for analysis.
“The natural behaviour of the thylacine was never scientifically documented,” said Professor Gregory Berns, a neuroscientist at Emory University in Atlanta, USA, who is the lead author of a paper about the research published today in the journal PLOS ONE.
“Our reconstruction of its white matter tracts, or neural wiring, between different regions of its brain is consistent with anecdotal evidence that the thylacine occupied a more complex, predatory ecological niche versus the scavenging niche of the Tasmanian devil.”
To make their findings Gregory and co-author Ken Ashwell, at the University of New South Wales in Sydney, used a kind of MRI technique called ‘diffusion tensor imaging’ (DTI) to scan the preserved brains of the thylacines and two Tasmanian devils. A relatively new technique, DTI is more useful than conventional MRI for studying preserved brains – rather than those of living or recently dead animals – and is good for picking out structural information.
DTI collects data on how molecules move through body tissues, and in this case revealed the structure of the connective pathways, or white matter, of the brains. Compared to the brain of its close relative the Tasmanian devil, the thylacine’s brain “may have had relatively more cortex devoted to planning and decision-making, which would be consistent with a predatory ecological niche,” the authors write.
Treasure trove of museum brains
“While it is easier to study the brains of animals that have recently died, we’ve shown that we can successfully use our scanning techniques on specimens that are 100 years old,” Gregory added. “We now have the technology available to make use of the treasure trove of museum collections around the world.”
Dr Bradley Smith, an expert on the psychology of dingoes at Central Queensland University said: “It is wonderful that technology and our understanding of brains has got us to the point where we can start to learn more about the Tasmanian tiger despite their long absence… This study has confirmed that, as a predator, they had to think differently than other marsupials, such as the devil. In essence, they thought more like a dingo.”
However, exciting though the find is, Bradley cautions that the tiny sample size of just two specimens limits the inferences that can be made from this work about the species as a whole.
It’s also “difficult to truly infer what the behaviour of the thylacine was like based on looking exclusively at their brains. Results need to be combined with other knowledge from other means, such as studies looking at the shape of their skulls and bite forces, which also tell us about their diet,” he said.
Animation of a 3D reconstruction of the white matter tracts of a thylacine’s brain. (Credit: Gregory Berns)
‘Brain Ark’ database of rare species
Gregory is now building an online database of digital scans of animal’s brains – ‘Brain Ark’ will include extinct species and will help researchers explore questions about brain evolution.
“We know a lot about the brains of primates and rats, but there are a lot of other animal brains out there that no one has looked at in any kind of detail,” he said. “The Brain Ark is going to fill that gap. We are living in a time when much of the planet’s megafauna is at risk for extinction. It’s important to gather as much data as we can before many of these animals disappear.”
“MRI imaging of the preserved brains of rare, extinct and endangered species is an exciting innovation in the study of brain evolution,” added Ken. “It will allow us to track pathways and study functional connections that could never be analysed with older experimental techniques. It also avoids the ethical and conservation problems of doing experiments on rare and endangered animals.”
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