February 28, 2012 | 2
Australia has a long history of invasive species that have damaged the island nation’s ecology and driven several species into extinction. The most famous example, of course, is the cane toad (Rhinella marina), which was introduced by Australia in 1935 in an attempt to control sugar cane pests, but which instead proved devastating to many species of frogs, turtles, and even salt-water crocodiles.
Another invasive species plaguing Australia is a beautiful flowering plant known as mother-of-millions (Bryophyllum spp.). Introduced from Madagascar as a garden ornamental, the plants quickly escaped from Australian backyards to more rural areas. Mother-of-millions plants, as their name suggests, reproduce prodigiously and don’t need much water, allowing them to outcompete native plant species. They are also highly poisonous, often claiming the lives of cattle that feed on the plants during drought.
But while mother-of-millions is an invasive species that has damaged the Australian ecosystem, new research shows it has one unexpected benefit: It is actually helping one lizard species to protect itself against the poisonous cane toad.
According to a study published in the March 2012 issue of American Naturalist, the toxins of cane toads and mother-of-millions plants are quite similar. When eastern blue-tongued skinks (Tiliqua scincoides scincoides)—shown above— in the states of Queensland and New South Wales ate the mother-of-millions plants, they gained a resistance to the cane toad toxins, known as bufadienolides. Cane toads are not present in that region, and the eastern blue-tongued skink is not a species at risk, but the cane toads endanger other species of blue-tongues in other parts of Australia.
Richard Shine, a biologist at the University of Sydney, and his colleagues had been studying the ecological impact of cane toads when they noticed that some lizard populations appeared to have a high tolerance to bufotoxins, even in areas where cane toads were not a threat. They collected blue-tongue lizards from places with and without mother-of-millions and injected each animal with a tiny amount of cane toad toxin. The result: the lizards from places where mother-of-millions is common had less of a reaction to the toxin than those from places where the plant does not exist. Shine and his co-authors say this suggests that eating the plant drove natural selection over a period of 20 to 40 generations and resulted in populations of lizards that could tolerate the bufotoxins.
“Now it appears,” Shine said in a prepared release, “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 [where the plants have not yet spread] continues. Eating this plant has pre-adapted the eastern ‘blueys’ against cane toad poisons.”
Shine says this will help the Australian government to fight cane toads by concentrating expensive eradication efforts on regions where mother-of-millions is not present and, therefore, where the toads have more of an impact on native species.
Previously in Extinction Countdown: “Don’t Eat That: Endangered Quolls May Benefit From Aversion Therapy”
Photo: Eastern blue-tongued skink via Wikipedia. Used under Creative Commons license