Eating poisonous invasive plants whetted the appetite of eastern Australian blue-tongue lizards for invasive cane toads and prepared the lizards for the plague of toxic toad invaders sweeping across the country.
The plant, mother-of-millions (Kalanchoe daigremontiana), happens to contain a toxin nearly identical to that of the cane toad (Bufo marinus). Richard Shine, a biologist at the University of Sydney, discovered that in areas where the plant has taken root in Australia, local skinks (Tiliqua scincoides) adapted to the deadly delicacy and gained immunity to the toad’s poison as well.
In other parts of Australia, blue-tongue skink numbers plummet when the toads arrive, since the omnivorous lizards die from the bufotoxins secreted by the toads, a native of Central and South America.
“Now it appears we have a population of eastern blue-tongue 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 in a press release. “Eating this plant has pre-adapted the eastern blueys against cane toad poisons.”
The mother-of-millions plant originated in Madagascar, but was brought to the Land Down Under as an ornamental. The plant fled the garden bed and is now a nuisance in Queensland and New South Wales.
The proliferation of the plants preceded the toad take-over. That gave local lizard populations a chance to evolve resistance to the bufotoxin years before the toads arrival.
“Our study was stimulated by a puzzling observation that arose during research on the ecological impacts of invasive cane toads … in Australia,” Shine and his colleagues wrote in a paper published in The American Naturalist. “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.”
To test their hypothesis, the biologists collected blue-tongues from areas with mother-of-millions and without. They then injected the lizards with small amounts of bufotoxin. The lizards from mother-of-millions habitat had a milder reaction. The results suggest that the reptiles evolved defenses to bufotoxins in only 20 to 40 generations, since mother-of-millions arrived in Australia about 70 years ago.
Knowing that these populations of blue-tongue lizards are safe from the rapidly spreading toads could change Australian conservation strategies.
“We’re now able to focus our conservation dollars on those populations that can’t care for themselves,”Shine said.
Blue-tongued skink (Tiliqua nigrolutea) displaying it’s tongue. (Wikimedia Commons, Benjamint444)