RUN, TOAD, RUN

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Science  05 Sep 2008:
Vol. 321, Issue 5894, pp. 1275a
DOI: 10.1126/science.321.5894.1275a
CREDIT: BEN PHILLIPS

Cane toad races are a barroom pastime in parts of northern Australia. Now the pestiferous amphibians are racing for science.

Researchers led by zoologist Michael Kearney at the University of Melbourne have been trying to predict the potential range of the country's plague of cane toads, which were first introduced in the 1930s to attack sugar cane beetles in Queensland.

The toads have been expanding their range roughly at a rate of 60 kilometers a year. To see how far south the population could extend, the scientists tried to gauge how far the animals can hop under various temperature conditions. They tested 89 toads on a 2-meter course, measuring hopping speed at five temperatures ranging from 15° to 35°C. Hopping speeds ranged from a molasses-like 300 meters per hour at 15°C to a brisk 2.2 km at 30°C, they report in the August issue of Ecography.

Combining data on toad movements with information on reproductive needs (ponds for eggs and larvae) and climate, the researchers predicted that, contrary to some previous analyses, the toads won't be invading major cities such as Sydney and Melbourne. Even with predicted climate change, they say, adults would be too slowed down by cool, dry weather to spawn or find enough to eat. Biologist A. Marm Kilpatrick of the University of California, Santa Cruz, who does research on the West Nile virus, calls it a “neat” study that “offers a bottom-up mechanistic way to look at an animal's distribution” by combining data on climate, physiology, and behavior.

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