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Poison Toads Leap Across Australia

Stephanie Peatling in Sydney, Australia
for National Geographic News
November 29, 2004
 
Small, warty, and armed with a poison strong enough to kill crocodiles,
the cane toad is generally regarded as a blight on the Australian
landscape.

Native to the Americas, the species was introduced to northern Queensland 70 years ago to control sugarcane beetles. The toads failed in that duty but spread across Queensland and into neighboring Northern Territory.

Now the interloper is poised to invade the states of Western Australia and New South Wales (NSW). NSW wildlife authorities fear the amphibians—which have poisonous backs that kill hungry predators—will have a devastating impact on native species.



Those fears may be about to be realized. Australia's leading government research body, the Commonwealth Science and Industry Research Organisation (CSIRO), forecasts a rise in average temperatures that will make NSW ideal habitat for the cane toad.

Tony Robinson, head of CSIRO's Wildlife, Pests, and Diseases Program, said climate change is increasing the amount of suitable habitat for the toad.

"With climate change, models have been produced that suggest [the cane toads] might go down as far as Sydney and some areas of Western Australia," Robinson said.

Recent estimates put the pace of the toad's westward march at nearly 17 miles (27 kilometers) a year and slightly slower from north to south.

More southerly cities, such as Melbourne and Adelaide, would likely remain too cold and dry to ever suit the toads, Robinson noted, but Perth could expect cane toads in five years' time.

Sydney could see their arrival in the next 20 years.

Predictions for temperatures in NSW show rises of up to 2 degrees Celsius (3.6 degrees Fahrenheit) by 2030, with longer, warmer summers and more rain along the coast. That's a prescription for the tropical conditions enjoyed by the cane toad.

It's Not Easy Being Brown

Robinson said there is no one strategy that will keep the toads under control.

The interlopers already cover at least half of Queensland and most of the Northern Territory, an area so vast that it would make locating and targeting the species a daunting task. The toads are believed to number in the billions.

A Venezuelan virus was tried in the 1990s but had to be abandoned after it was found to also kill native frog species.

Robinson said the "hunt is on" for the solution.

It is hoped that the toad's insides—particularly their immune, digestive, and circulatory systems—will provide some clues.

A one-million-Australian-dollar grant from the Australian government is helping the research team identify a gene that is critical for the toad's metamorphosis from tadpole to adult.

"If this gene can be expressed early in the tadpole stage, the cane toad should see the gene product as a foreign entity and initiate an immune response against it," Robinson explained.

"Such a response should interfere with metamorphosis, preventing the toad from maturing and reproducing," he said.

A colleague, Alex Ryan, is working on whether the specific developmental gene can be transferred using a "ranavirus"—a naturally occurring virus that can infect amphibians and fish—as a carrier.

"Because ranaviruses are large, double-stranded DNA viruses, it should be possible to delete a viral gene and insert the development-controlling gene in its place."

Although the researchers believe they are not far from demonstrating the process can work, it will take another decade to run the trials that must be conducted before a general release.

Official Pest

Scientists and governmental bodies believe a national approach is needed.

Northern Territory Parks and Wildlife Minister Chris Burns said, "The protection of our unique environment and ecosystems is a priority."

The main threat the toads pose to species such as dingos (wild dogs), quolls (cat-size marsupials), goannas (Australian monitor lizards), and crocodiles is the poison contained in glands on each of the frogs' shoulders. The venom squirts out when the toads are threatened or handled roughly.

The poison is made up of 14 different chemicals. Together they cause rapid heartbeats, excessive salivation, convulsions, and paralysis.

Cane toads also compete, and usually win, the hunt for food and habitat.

Burns said the Australian government has the resources to coordinate a national approach to the problem, including identifying what research still needs to be done.

The newly established National Cane Toad Taskforce will examine whether official recognition of the cane toad as a threatening species under federal environmental laws would help accelerate the amphibian's demise.

Listing the cane toad under Australia's Environment Protection and Biodiversity Conservation Act would put the onus of responsibility for action onto the federal government if the toads were found to be wreaking havoc on native species.

"If the [federal government] and other states combine resources, I believe we can achieve a very substantial biological-control research program," Burns said.

Some Aussies have found comic relief in the cane toad invasion. Earlier this year Australia's National Rugby League released a television commercial featuring the Queensland rugby captain laughing as he stealthily released cane toads into a rival team's Sydney sports stadium.

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