Seeker Archives

Toxic Toads Evolving Quickly : Discovery News

Invasive cane toads in Australia are adapting to territories unlike those in their native South America, surprising ecologists and spreading faster than ever.

The infamous quick-evolving cane toads that have been invading Australia for 70 years appear to have adapted so well that they might conquer twice as much of the continent than was first predicted.

The original invasion models apparently failed to predict that the toads would adapt to Australian habitats so quickly. The fact that the toads are becoming more Australian as they invade -- spreading further, faster -- has big implications for the study of invasive species around the world.

It's also a glimmer of good news for some native species facing climate changes: They too may be more able to adapt and survive changes than expected.

The original predictions came from comparing the toad's native habitat in South America to habitats with the same physical attributes in Australia.

"You use the envelope where they came from," explained evolutionary biologist David Skelly of Yale University. That work was done in the 1980s, revealing that the toads had already reached limits similar to those at the edges of their ranges in South America.

But instead of stopping there, the toads are still spreading, and faster than ever.

"All of a sudden in the last 10 years it changes," said Skelly. "They're moving into areas where they physical environment is not like anything in their native range."

That implies that the cane toads have evolved more tolerance for the hotter climates they are now encountering. This is on top of the discovery last year that the toads at the forefront of the invasion had evolved longer legs than those in the interior of their range.

The ability of animals to evolve so quickly needs to be factored into invasions, or the dangers of invasive species will likely be underestimated, argue Skelly and his colleagues Mark Urban, Ben Phillips and Richard Shine in an article in the March 28 issue of the Proceedings of the Royal Society-B.

"The velocity of evolution is fast enough that you have to think about this," Skelly told Discovery News.

Ditto for the ecologists who are modeling how climate changes are likely to affect many species, Skelly said.

To date, most ecological models assume little or no ability for species to rapidly adapt to a new environment, he said. A more dynamic model would allow for more flexibility, which apparently exists in some species with quick lifecycles - which means more opportunities for natural selection to breed a species better adapted to a changing world.

As if to underline the importance of the new study, frog watchers in Australia last week announced the capture of a record-breaking cane toad. The mammoth toad measured nearly eight inches (20.5 cm) long and weighed in at almost two pounds (861 grams).

"The biggest toads are usually females but this one was a rampant male," reported Graeme Sawyer, coordinator of a group called FrogWatch. "He is huge, I would hate to meet his big sister."

The giant was caught in Lee Point, in Australia's Northern Territory. It was nearly double the weight of the last record toad caught there recently, which was a female.

Cane toads were deliberately imported to Australia in 1935 with hopes they would control scarab beetle infestations in sugar cane fields. Unfortunately, the toads did not eat the beetles, but began an invasion that is detrimental to native wildlife and continues today.