Toxic Toads Evolve Longer Legs, Study Says

February 15, 2006

New generations of cane toads in northern Australia have longer legs than those in older populations, according to a new study.

The longer legs are allowing the toxic toads to spread even faster to new territory.

Cane toads (Bufo marinus) are native to South America and can weigh up to 4.4 pounds (2 kilograms). They were introduced to Australia in 1935 to combat beetles that were devouring sugarcane crops.

But the toads began snapping up other bugs instead and quickly started competing with and beating out native insect-eaters.

The toads are also toxic, which means most predators die after eating the amphibians.

Thanks to these favorable conditions, the toads currently occupy more than 390,000 square miles (1 million square kilometers) of the continent.

When the toads were first introduced, they spread at a rate of about six miles (ten kilometers) per year. Today cane toads advance more than 31 miles (50 kilometers) annually.

This faster pace is happening, at least in part, because toads at the forefront have about 10 percent longer legs than toads of earlier generations, said Richard Shine, an ecologist at the University of Sydney in Australia.

Shine's team will report the find in tomorrow's issue of the science journal Nature.

Toxic Toads

No documented extinctions are attributed to the cane toads, Shine said. But the animals dramatically modify the abundance and diversity of plants and animals in the ecosystems they invade.

Shine said his finding is the latest example of how natural selection complicates the conservation challenge presented by the invasive species.

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