Beware the toxic road!

Natural History, July-August, 2006 by Nick W. Atkinson

Evolution has a way of fighting back. Nowhere is that process more visible than in Australia, where one species of snake is mounting a defense against the cane toad, an ever-encroaching menace. The toad, which can weigh three pounds, was introduced in 1935 in an early attempt at biological control of sugar cane's insect pests. Alas, that well-meaning act unleashed an ecological disaster. Cane toads are toxic enough to kill a person. In addition to devouring native insects and small vertebrates, they've been decimating would-be toad predators, including certain lizards, marsupials, and snakes.

Ben L. Phillips and Richard Shine, biologists at the University of Sydney, are studying the impact of cane toads on Australia's native red-bellied black snake (Pseudechis porphyriacus). In a series of experiments, Phillips and Shine have shown that certain populations of the snake have evolved not only to avoid the toads, but also to resist their toxins (to a degree). Those characteristics are hard-wired into the snake's genome. The longer a snake population has been exposed to cane toads, the more likely its members are to avoid eating the toads, and the greater their resistance to toad toxins.

Does the snake's evolution offer a glimmer of hope for conserving Australia's native species? Perhaps. But Phillips and Shine have also shown that cane toads at the advancing front of an invasion are evolving longer legs, which enable them to disperse ever more quickly. (Proceedings of the Royal Society B, doi10.1098/rspb.2006. 3479, 2006)