Invasive plant prepares native lizards for a toad fight
INVASIVE animals or plants are known for their devastating impact on the ecosystem, often pushing some native species to extinction. But Australian researchers have spotted an invasive plant which is preparing local predators for the arrival of another invasive species—the notorious cane toad.
Rhinella marina, as the toad is known in scientific parlance, was introduced in Australia in the 1930s to control beetles that destroy sugarcane crops. But it soon became an ecological disaster of its own. It produces a toxin called bufadienolides, which has proven deadly to many native Australian species that feed on it. Bluetongue lizard is one such vulnerable species. Its population in northwestern Australia began to shrink significantly after the toad arrived in the region.
While studying the ecological impact of cane toad in Australia, Richard Shine, a biologist at University of Sydney, and his team encountered a puzzling observation. Some lizard populations were vulnerable to bufotoxins whereas others were not. The population with high tolerance to bufotoxins included some that had never been exposed to the toad, the researchers note in the study paper published in the March issue of the American Naturalist. Why would lizard populations in eastern Australia develop a tolerance to the toad toxin when no toads were present in the region?
The answer, according to the team, is likely to be an ornamental plant, mother-of-millions (species of Bryophyllum), which produces a toxin virtually identical to the toad toxin. After it was imported from Madagascar some 70 years ago, the plant has weeded out several native plants in parts of Queensland and New South Wales, and become part of the diet for local bluetongue lizards.
Shine and his team collected samples of all three species from different regions of Australia and conducted various genetic studies and toxin-tolerance trials to arrive at the conclusion. They found that the toad toxin had a little effect on lizards from places where the plant is common than on those from regions where it was absent. The results suggest the plant drove strong selection for lizards that tolerate the toad toxin and the evolution occurred over a relatively short period of 20 to 40 generations.
The study will help the Australian government fight cane toads in an effective manner by concentrating expensive eradication efforts on regions where mother-of-millions is not present. Sanjay K Das, herpetologist at Guru Gobind Singh Indraprastha University in New Delhi says the study sets a good example of strategic management of species of conservation importance in countries that face threats by various invasive species.