The Tasmanian tiger, also known as the Thylacine (Thylacinus cynocephalus), was a major predator in Australia and surrounding regions for millions of years. The last one to be seen, however, was in 1936 and since then they are believed to have gone extinct.

Most people assumed that they went extinct largely because of human influence. When European settlers came to Australia, they introduced new stressors to the animals. As people settled in different areas, they would hunt the Tasmanian tiger because it was considered a pest that would eat their livestock. In addition, dogs were introduced to the region, which made survival more difficult for the animal.

While both of these things undoubtedly contributed to the hastening of extinction for the animal, a new study published in the Proceedings of the Royal Society says that they were likely headed to that fate for much longer. In fact, it says that the loss of four key genes sometime over a million years ago might have led to their downfall. In the paper, the team explains:

“The thylacine genome exhibits the loss of four genes—SAMD9L, HSD17B13, CUZD1 and VWA7—each with important biological functions and implications for species fitness. Our investigation into the timing of gene loss events revealed a staggered pattern, occurring over a span of approximately 13−1 [million years ago].  This temporal distribution indicates that the gene losses were not confined to a single evolutionary event but occurred progressively after the Middle Miocene Climate Transition.”

This transition time took place sometime between 15 and 13 million years ago and it is considered to be a major ecological and climate change. The ancient ancestors to the Tasmanian tiger would have been a lot smaller at the time. The animal evolved to become larger, which may have been the result of the gene changes, or the cause of them.

Those four genes, however, were important for the species immune functions, including key antiviral and anti-tumor abilities. In addition, around the same time, the Tasmanian tiger experienced a reduction in its olfactory receptor genes. This reduction in sensitivity to smell indicates that the species was moving from hunting by scent to relying more on sight and hearing. the team says:

“Unlike the Tasmanian Devil, a scavenger, the taller thylacine likely depended on vision and sound for hunting, aided by its ability to see over vegetation.”

While the team does not know what exactly triggered these evolutionary changes, the loss of those genes made the species less able to survive in the world of the future. This does go to show that some evolutionary changes that have benefits at the time can actually cause problems for future generations. The team said:

“Whatever the cause for gene loss, the loss of SAMD9L, HSD17B13, CUZD1, and VWA7 genes in the thylacine possibly had negative pleiotropic effects, potentially compromising its health by affecting antiviral defense, metabolic processes, lactation, pancreatitis, and tumor susceptibility. Although model-based population viability analyses suggest that the disease played only a minor role in thylacine extinction, other studies suggest that a ‘canine-distemper-like’ disease played a role in exacerbating its extinction.”

Of course, this does not let humans off the hook entirely. Just because the Thylacine’s evolutionary path made their survival more difficult, they likely could have been fine for thousands of years more if it weren’t for the actions of people.

This study does, however, provide a more complete picture regarding what led to the extinction of the Tasmanian tiger and that information may help conservationists to protect other animals going forward.

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