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Thylacine Had Brain Structure Suited to Predatory Life Style

A duo of researchers from the United States and Australia has used an imaging technique to reconstruct the brain architecture and neural networks of the thylacine (Thylacinus cynocephalus), the most iconic animal of Tasmania.

A pair of thylacines, a male and female, c. 1905. Image credit: Smithsonian Institutional Archives / E. J. Keller, National Zoological Park.

A pair of thylacines, a male and female, c. 1905. Image credit: Smithsonian Institutional Archives / E. J. Keller, National Zoological Park.

The thylacine, also known as the Tasmanian tiger or the marsupial wolf, was a carnivorous marsupial and the apex predator in Tasmania.

This species looked like an amalgam of several animals. It is one of only a few marsupials to have a pouch in both sexes.

The animal was the size and shape of a medium-to-large size dog, but had tiger-like stripes running down its lower back and an abdominal pouch.

The fossil record shows that the thylacine appeared about 4 million years ago in Australia. By the 20th century it was extinct, or extremely rare, on the mainland but was still found in Tasmania, the island state off Australia’s southern coast.

The species’ demise can be directly attributed to the bounty scheme in place from 1830–1914 that resulted in the killing of several thousand animals and indirectly to the loss of its habitat from farming activity.

The last known thylacine died in 1936, in Beaumaris Zoo in Hobart, Tasmania, and little is known about the species’ natural behavior. The only records of behavior in their natural habitat are stories passed on by farmers, hunters, and trappers.

However, some behaviors can be inferred from brain structure, so Dr. Gregory Berns of Emory University and Dr. Ken Ashwell of the University of New South Wales scanned thylacine brains and reconstructed neural connections.

The researchers used magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) to scan two thylacine brain specimens, both of which were about 100 years old.

“Only four surviving specimens of the brains of Tasmanian tigers exist, and the study gained access to two of them,” the authors explained.

“One was provided by the Smithsonian Institution, taken from a male Tasmanian tiger after it died at the National Zoological Park in 1905. The other specimen, loaned to the researchers by the Australian Museum in Sydney, came from an animal that died during the 1930s.”

This image shows the neural pathways of the Tasmanian devil (left) and the thylacine. Image credit: Emory University.

This image shows the neural pathways of the Tasmanian devil (left) and the thylacine. Image credit: Emory University.

Dr. Berns and Dr. Ashwell also compared the structure of thylacine brains with that of Tasmanian devil brains.

They found that thylacine brains had larger caudate zones than Tasmanian devil brains.

This suggests that thylacines devoted more of their cortex to complex cognition, particularly action planning and possibly even decision making.

This fits with the ecological niches of these two animals: Tasmanian devils are scavengers while thylacines were hunters, and the latter foraging strategy entails more planning.

“The natural behavior of the thylacine was never scientifically documented,” said Dr. Berns, corresponding author of a paper describing the research, published this week 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.”

“The thylacine appears to be an example of convergent evolution, filling a similar niche that members of the canid family did elsewhere,” Dr. Berns added.

“It’s interesting, however, that the thylacine brain is very different than the canine brain, despite the physical resemblance of their bodies.”

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G.S. Berns K.W.S. Ashwell. 2017. Reconstruction of the Cortical Maps of the Tasmanian Tiger and Comparison to the Tasmanian Devil. PLoS ONE 12 (1): e0168993; doi: 10.1371/journal.pone.0168993