Rampaging cane toads Down Under falling prey to arthritis

November 14th, 2007 - 2:20 am ICT by admin  
According to the study, the faster they travel, the more likely their joints hurt.

Cane toads (Bufo marinus) were introduced into northeastern Australia in 1935 to control crop-eating insects.

But they spread quickly, and have been blamed for declines in native animals in colonized areas.

Today, ecologists and farmers are doing their best to keep the invading hoards from expanding any further.

Now, lead author Rick Shine and his colleagues have found that toads at the front of the invading population are suffering from arthritis as a result of their fast-hopping travels.

Shine had previously shown that toads at the invasion front seemed to have longer legs than those trailing behind, allowing them to conquer more territory more quickly.

While conducting this research, Shine noticed a high number of spinal abnormalities in the advancing cane toads.

By examining preserved specimens taken from invading and established toad populations, Shine and his co-researchers found that about 10 percent of large invading adults had severe spinal arthritis - which in toads manifests as bony growths fusing the joints between vertebrae.

By looking at live populations, Shine and his colleagues further determined that the faster, larger toads were more likely to have arthritis.

“Basically, the body plan of frogs [and hence toads] has evolved to support a fairly sedentary lifestyle: sit beside the swamp, catch bugs, et cetera. The invasion process has put very different pressures onto cane toads, and has resulted in the evolution of an animal that, based on radiotracking, moves long distances and does so every night. This gives the toads access to more food, but isn’t doing their joints any favours,” said Shine.

Surprisingly, arthritis didn’t seem to hinder the toads’ invasion, the study found.

Shine raced arthritic toads against healthy ones. He found that on a 10-metre runway, the arthritic toads quickly slowed down compared with their healthy brethren. However, when toads were fitted with radio transmitters and released into the wild, the arthritic toads seemed to move just as far as the healthy critters.

“Toads are incredibly stoic animals. We confidently expected that the arthritic toads would travel less far under field conditions than same-sized non-afflicted toads. Instead, the arthritic toads simply keep on going. They can’t keep moving rapidly for long distances, and are forced to take shorter hops. But they keep going nonetheless,” Shine said.

Shine said the idea that an introduced animal capable of establishing itself and decimating local wildlife was under severe stress, was a novel one.

“In my experience this is a totally unprecedented observation. Thinking about the costs of invasions is something that deserves our attention. This is going to change how researchers in the field think about their systems,” said Dave Skelly, an amphibian expert at Yale University in Connecticut.

Shine and his colleagues report their study in the Proceedings of the National Academy of Sciences, reports Nature. (ANI)

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