Toxic Toad Eaters Reveal How Evolution Repeats Itself

Invasive species extraordinaire and one helluva toxic toad. Photo by Chris Ison At the time, it seemed like the logical thing to do. Australian farmers were desperate. It was the 1930s, and beetles were tearing through their crops, especially sugar cane. Word spread of a toad that loved to gorge itself on the problem pests, which had been successfully brought to Hawaii to manage beetles in sugarcane fields. The Australians could have turned to pesticides, sure, but pesticides are expensive and often harmful to people and the environment. And if the toad could be introduced once, why not again? Why shouldn't they fix their bug problem once and for all with a harmless little amphibian? So in 1935, two suitcases of cane toads (Rhinella marina; formerly Bufo marinus) arrived in Australia. Those toads would go on to produce more than 1.5 billion descendants, contending for the title of worst invasive species in history. The cane toads didn't eat the beetles they were brought in to eradicate, but they do seem to eat everything else that fits in their fairly large mouths (the animals can get over 1 ft long and weigh several pounds!). Equally damaging is the fact that nothing on the continent can eat them — like other Bufoid toads, cane toads are armed with a potent poison that can kill unprepared predators hoping for a quick bite of cuisses de grenouille. The type of toxins they wield, called bufotoxins, strike at the heart. When a potential predator ingests the toad's defensive slurry, the toxins make their way through the blood to the cardiac muscle, where they bind to one of the key molecular components of contraction: a pump that moves sodium and potassium ions across cell membranes. Without this pump functioning, the heart cannot beat how it is supposed to, leading to life-threatening conditions and, often, death. Predatory animals in Australia didn't evolve with these toxic toads, so they have no natural defenses to the toxins, and the results have been devastating.