The extinction of crucial genes over the millennia since humans arrived in Australia may have made the thylacine more prone to extinction.

The thylacine, also known as the Tasmanian tiger (Thylacinus cynocephalus), was the last remaining member of a marsupial family called Thylacinidae, which once thrived in Australia and New Guinea.

It became extinct on mainland Australia around 2000 years ago, primarily due to human hunting and competition with dingoes. After European settlers arrived in Tasmania, the animal was targeted by farmers and government bounties, leading to the last of its kind dying in 1936 at Hobart Zoo.

Nagarjun Vijay and Buddha Bhashan Gilish Salv from the Institute of Science and Education in Bhopal, India, grew fascinated by the Tasmanian tiger’s genome while studying that of the Bengal tiger (Panthera tigris tigris).

“We noticed some parallels between the extinction of thylacines and our own tiger,” Vijay notes. “There’s a significant push to protect Indian tigers.”

The duo theorized that hypercarnivores like the Bengal and Tasmanian tigers may have lost vital genes through their evolutionary journey in response to environmental shifts and emerging diseases.

They examined genetic data previously obtained from thylacine specimens and compared these to the genome of the Tasmanian devil, a close relative (Sarcophilus harrisii), along with other marsupials.

Unlike nearly all other marsupials, including the Tasmanian devil, the thylacine has lost at least four crucial genes: SAMD9L, HSD17B13, CUZD1, and VWA7.

Vijay found it surprising that this genetic loss did not occur after Tasmania’s populace was isolated due to rising sea levels roughly 10,000 years ago.

This genetic loss may have been beneficial under certain historical conditions, but can hinder species health by diminishing antiviral defense, metabolic functions, lactation, as well as increasing susceptibility to cancer and pancreatitis.

Thylacines lost SAMD9L, CUZD1, and VWA7 at least 6 million years ago, coinciding with a significant climatic transition when species sizes increased dramatically, resulting in an oversaturation of carnivores entirely dependent on meat.

“The overarching narrative is that much of the human influence, or artificial changes, has perpetually shaped the extinction of thylacines,” Vijay states. “We speculated that there would be lost genes linked to disease, and that’s exactly what we uncovered.”

Timothy Churchill from the University of New South Wales in Sydney emphasizes that climate change over the course of human history has indeed led to a drastic decrease in genetic diversity among thylacines. He believes that the genetic losses identified in the new study may have rendered the Tasmanian tigers more vulnerable to illnesses, though confirming this requires additional research.

“It’s one of those species that truly survived against the odds for an extended period in that niche,” Churchill explains. “But once dingo-like canids arrived, it was the beginning of the end on the mainland. Then, of course, after creating adversaries in Tasmania, it marked their doom.”