Cane toads are seemingly innocuous enough. First imported to Australia to control a beetle pest of sugarcane fields, they are now frog-marching their way across the island continent, wreaking havoc on in situ flora and fauna. The key to their domination has been protection from would-be predators and an ability to breed fast. But how were cane toads gifted with those traits in the first place?

A new study published February 5 in Science aims to answer that question. Biologist Ines Van Bocxlaer of Vrije University Brussels and her colleagues analyzed the kinds of traits that allow various toad species to thrive under many conditions and thereby expand their ranges: independence from constant access to water and humidity; glands that produce poison as protection from predators (which double as water storage); and an ability to lay large amounts of fast-hatching eggs in temporary waters, among others. Perhaps most surprisingly, at least in the case of toads, bigger body size is better. Unsurprisingly, the cane toad—and many of its 500 Bufonidae family brethren—shares most of these traits, including a propensity for quick adaptation and blitzkrieg-like range expansion.

The toad family originated in the tropics of South America before colonizing the rest of the globe. That initial colonization was set off, according to this new analysis, by the development of this set of traits, which has subsequently allowed most conquests of new territories, such as the expansion of toads from tropical niches in India to more diverse, drier habitats. In fact, this may explain why toads that are only distantly related genetically often share so many of the same traits: Conditions cause the various species to converge back on the traits of the same ancestral range-extending type of toad.

Those toads that do not share these traits, such as the harlequin, are not doing as well. Climate change is making life more difficult for specialized amphibians of all kinds, and amphibian chytrid fungus, an infection that is helping to wipe out populations around the globe, afflicts as much as 50 percent of extant amphibians.

That said, the cane toad may just be living up to its genetic legacy. "The origin of this range-expansion ability," Bocxlaer wrote, "appears to be rooted deep in the evolutionary tree of toads and may be a remnant of when toads colonized the world."

Slide Show: How Toads Conquered the World

5 Comments

1. 1. wildeerman 10:44 AM 2/7/10

   I'm interested in biological writings, astronomy, history an arts. I hope that your page deals wit those aspects.

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2. 2. wildeerman 10:47 AM 2/7/10

   I'm interested in biology, history, astronomy, art and culture, but I'm not a scientis, only an amateur.

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3. 3. Paul First 08:18 PM 2/8/10

   from cane toad I think of pollar bear, what will happen if pollar bear were introduccd to Antarctic area?

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4. 4. luvmemo 11:32 AM 2/10/10

   I find this article intersting because the case of these cane toads was discussed in my biology class. This extra bit of information made it clear why those toads were able to handle the hot and dry climates of Australia even though their prior habitat differed from that of the new one.

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5. 5. Jenny lopej 12:34 AM 12/24/10

   The cane toad is native to the Americas and its range stretches from the Rio Grande Valley in the southern Texas to the central Amazon and the south eastern Peru. This area encompasses both the tropical and the semi arid environments. The density of the cane toad is significantly lower within its native distribution than in the places where it has been introduced. In the South America, the density was recorded to be 20 adults per 109 yards of shoreline, 50 to 100 times lower than the density in the Australia.
   http://www.wildlifeworld360.com/venomous-cane-toads.html

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