The introduction of cane toads to Australia in the 1930s would become a textbook example of invasive calamity. Their flesh is poisonous, they lacked native predators, and unwitting animals who tried to eat them often died. Dramatic declines in many species followed the toads’ spread across the continent. Nearly a century later, though, many of Australia’s animals have started to adapt, and there’s reason to hope that the cane toad invasion will end with coexistence rather than ecological apocalypse.
In some cases, the adaptations have been physical, as with snakes who evolved smaller jaws that made it physically impossible to consume toads. In others, the adaptations have involved behaviors, like raptors eating only venom-free parts of toads. The latest addition to this toad-proof menagerie: scattered populations of northern quolls, a small carnivorous marsupial, avoid cane toads altogether.
As described in the journal Behavioral Ecology by ecologists Ella Kelly and Ben Phillips of the University of Melbourne, northern quolls were once found throughout northern Australia. Largely because of cane toads, they’re now endangered. Yet a few remnant populations have persisted. They’re not physically immune to the toads’ poison. Instead they seem to be “toad-smart,” write Kelly and Phillips, who to learn more about the mechanisms underlying this intelligence captured 58 quolls from toad-exposed and toad-free locales and tested their responses to toads.
The researchers presented each quoll with a dead adult toad inside a cage. Those from toad-free locales were quick to inspect the cage and tried to bite the toad inside. Quolls from toad-exposed locales mostly ignored the amphibians. Maybe they possess some innate, genetically-based tendency to avoid toads, surmise Kelly and Phillips. They might also have acquired that lesson culturally, learning from their mothers and by watching other quolls. Or both factors could be involved, with these survivors descended from particularly brainy individuals whose propensity for learning helped them stay alive as a new, delicious-looking and deadly prey arrived on the landscape.
Future research should reveal more about the mechanisms. In the meantime, the captured quolls are being kept as part of a captive breeding program, and Kelly and Phillips hope to spread their behaviors. Areas where northern quolls have been decimated might be repopulated with toad-smart individuals who can pass on their genes or the lessons they’ve learned. “Behavior is increasingly becoming recognized as an important tool” for conservation, says Kelly.