The Species Evolving in the Wrong Direction

An adorable but critically endangered species of marsupial is evolving to be more vulnerable to predators, going in the opposite direction to what scientists want it to in order to survive.

These marsupials, named woylies, or brush-tailed bettongs, are critically endangered, living mostly in predator-free reserves in Australia to help increase their population.

However, due to lack of exposure to predators, some populations of these marsupials are rapidly evolving to lose their predator street-smarts, according to research published in the journal Biological Conservation.

"If they're not able to respond appropriately to predators, and we can't put them back in the wild, it just means that our conservation measures might not be as effective as we hoped," Tash Harrison, lead author of the paper and Ph.D. student at the University of Western Australia's School of Biological Sciences, told ABC News Australia.

Woylies are small, gerbil-sized marsupials native to western and southern Australia. Once common across the country, these critters were wiped out by the introduction of red foxes and feral cats, which eat the small mammals, as well as the arrival of the European rabbit which may have outcompeted the woylies in terms of habitat and food. Listed as "critically endangered" on the IUCN Red List, their populations were seen to have dropped to only around 5,600 individuals by 2011, and now sit between 12,000 and 18,000.

Now, however, after being kept safe from the predators that threatened their very existence, the woylies are evolving not to be able to keep themselves alive.

The researchers examined 10 years of data from woylies inside the Perup sanctuary, a protected haven near the town of Manjimup in the southwest of Western Australia, and compared it to data from a population living in the wild nearby. This is one of the two remaining wild populations left.

"We found that after 10 years inside the haven, our population of woylies have weakened anti-predator responses," Harrison said. "So they've become less reactive, less likely to run away from predators."

"They've become smaller, their feet have become shorter because without foxes and cats to run away from, it's less benefit to being big and they've also lost some of their natural anti-predator responses like ejecting the young as an escape distraction," she said.

This may mean that a different conservation strategy is needed to keep the woylies from the brink of extinction, such as exposing them to low-level predation in order to keep that selection pressure in the evolution equation.

"If, like woylies, other species in the havens are losing their street smarts for life in the presence of foxes and cats, it means that we are essentially making them dependent on living life in havens, and potentially limiting our ability to recover the species across their former ranges in the wild, without complete removal of foxes and cats," Adrian Wayne, a senior research scientist with the Department of Biodiversity, Conservation and Attractions and a research fellow at the University of Western Australia, told ABC News. "And that's a colossal challenge at the moment."

Exposing the animals to one fox or one cat, or less deadly predators like western quolls, to prevent predator defense traits from being lost to the tides of evolution may help the marsupials be able to finally return fully to the wild.

"Which means that not only do they flourish, but they also keep their smarts that are necessary for their long-term conservation and recovery in the wild," Wayne said.

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