Cute Quolls Taught to Dislike Toads

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The northern quoll (Dasyurus hallucatus) is an adorable little nocturnal marsupial about the size of a cat. It lives in northern Australia and eats fruit, insects, lizards, small mammals and toads. But the quoll's toad-loving habits are driving the species towards extinction.

Cane toads (Bufo marinus), native to Central and South America, were brought to the continent in 1935 to control beetles that were threatening sugar cane crops. The toads, however, became invasive and have spread across most of Australia. The toads are toxic, which means they cannot be controlled by native predators, like the quolls.

When the quolls eat large cane toads, the quolls are quickly poisoned and die. The toads are currently found in about 60 percent of the quoll's range and are expected to spread to the rest of the area within the next 20 years. Researchers moved some quolls to two toad-free islands to prevent the species' extinction, but what if there was a way to prevent the quolls from eating the toads? What if they could make the quolls think that cane toads weren't tasty treats? A new study in the Journal of Applied Ecology has a potential answer to these questions.

Researchers from the University of Sydney started with 62 young quolls and split them into two groups. One group was fed a tiny cane toad that was not big enough to kill the marsupial but was laced with a chemical called thiabendazole that induces a feeling of nausea. By eating it, the scientists reasoned, the quolls would learn that cane toads are bad to eat. The other group of quolls had no exposure to cane toads. The quolls were then presented with a small live toad. Those quolls that had been taught that toads tasted bad were more likely to ignore the live toad and less likely to attack it.

The scientists then fitted the quolls with radio collars and released them into the wild. The animals that had been taught to dislike toads survived up to five times longer than quolls in the other group.

The researchers need to do more work to determine if this learned aversion to toads is long lasting (and even then it's not fool-proof; two quolls fed the chemical-laced toad died from eating cane toads in the wild), and they'll also need to find a way to teach large numbers of quolls outside the lab. One possibility that the researchers envision is aerial deployment of "toad baits" in regions where the cane toads have yet to spread, to educate the marsupials, and maybe even other species, that cane toads are not good eats.

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