Cane toads, introduced in Australia in the 1930s to control a beetle pest in sugar cane crops, quickly became an ecological disaster of their own because they produce toxins called bufadienolides, deadly to many native Australian species that feed on frogs and toads, an article in The American Naturalist reported.
Bluetongue lizards are one of the vulnerable species, but some bluetongue populations seem less vulnerable to the toxins, researchers said.
"Some lizard populations were vulnerable to bufotoxins whereas others were not -- and the populations with high tolerance to bufotoxins included some that had never been exposed to toads," researcher Richard Shine of the University of Sydney said.
The reason, Shine and his colleagues said, is likely an invasive plant species known as mother-of-millions, imported from Madagascar as an ornamental plant, that has become part of the diet of bluetongues in some regions and happens to produce a toxin that's virtually identical to that of the cane toad.
The researchers suggest the plant drove strong selection for lizards that could tolerate bufotoxins -- a remarkable example of evolution over a relatively short period of some 20 to 40 generations of lizards.
"Now it appears we have a population of eastern bluetongue lizards that are able to defend themselves well against cane toads -- even though they've never actually met one -- whereas the devastation of the cane toads on the northwestern lizard population continues," Shine said. "Eating this plant has pre-adapted the eastern blueys against cane toad poisons."