Can Scientists Save an Endangered Marsupial by Breeding Out Its Taste for Poisonous Toads?

Some northern quolls do not eat deadly cane toads. New research suggests their aversion is an inherited trait

Wildlife Explorer/Wikimedia Commons

The northern quoll is being driven towards extinction by its deadly snacking habit.

Cute little marsupials with bushy tails and speckled fur, northern quolls love chowing down on cane toads, an invasive species that was introduced to Australia in the 1930s. But the flesh of the cane toad is poisonous, which in turn has caused northern quoll numbers to plummet. So now, as Robin McKie reports for the Observer, Australian scientists are trying to save northern quolls by breeding out the genetic trait that fuels their appetite for poison toads.

Previously, researchers tried to teach northern quolls not to eat the dangerous snack. In 2010, a group of quolls was fed dead cane toads that were too small to kill the marsupials, laced with a nausea-inducing chemical. When these quolls were subsequently presented with live cane toads, they were reluctant to eat the amphibians, suggesting that quolls can develop a learned aversion for cane toads.

But the technique wasn't foolproof, as some quolls still ate the toads, even after conditioning. And scientists also suspected that some quolls are genetically inclined to steer clear of the deadly prey. In areas of northeastern Australia, small populations of quolls do not attack cane toads, and they continue to thrive as their toad-loving neighbors decline. Ecologists at the University of Melborne hoped to selectively breed these toad-averse quolls and transport them to areas where cane toads have yet to invade. That way, when the amphibians do arrive, quoll populations will be pre-adapted to stay away from them.

First, however, the researchers had to prove that toad aversion is in fact an inherited trait. In a paper published recently in Conservation Biology, the team says it conducted a “common garden experiment,” collecting both quolls that have survived in toad-infested areas of Queensland, and quolls that live in areas without any toads. The researchers then bred three groups of quolls in captivity: some had two toad-averse parents, others had two parents that had never been exposed to cane toads, and still others were hybrids with one toad-averse parent and one toad-naïve parent.

During the next phase of the experiment, researchers presented the quoll offspring with the leg of a cane frog, which was too small to cause them any harm. They found that quolls with two toad-averse parents were “much less likely” to eat the leg than those with two toad-naïve parents. Interestingly, the hybrid offspring also tended to reject the toad leg. According to the researchers, this suggests not only that toad aversion is passed down genetically, but also that it is a dominant trait.

According to Brittany Hope Flamik of the New York Times, the ecologists recently took their experiment to the wild, releasing 54 mixed-gene quolls on Indian Island off Australia’s Northern Territory. Transporting organisms with desirable traits to new areas, in the hope that they will breed with existing populations, is known as targeted gene flow. In this case, the scientists were hoping that the quolls would give birth to ones that knew not to eat the toads. And lo and behold, when researchers checked on the quolls earlier this year, they found that a small number of their offspring had survived.

“Being born on the island and surviving to adulthood means these quolls received toad-smart genes and do not eat toads,” Ella Kelly, one of the authors of the paper, tells Observer’s McKie. “This shows that targeted gene flow can work.”

Selectively breeding northern quolls can’t eliminate all of the risks that the critters’ face; they are also threatened by habitat loss and predation by feral cats, for instance. But the recent experiment suggests that steps can be taken to save quolls by homing in on favorable genetic traits.

Targeted gene flow could one day be used to protect other endangered species, like the Tasmanian devil, which is being decimated by an infectious facial tumor disease. Some populations in Tasmania appear to have genetic resistance to the illness—and like toad-averse quolls, they may one day be bred to aid in the survival of their species.