Being a successful invader is a double-edged sword if you are a cane toad, say researchers. They have found that the front-line infantry of the invading waves of amphibian pests are showing signs of stress associated with their success: roughly one in ten suffers severe arthritis.
Cane toads originate from South and Central America and were introduced to Australia in 1935. They owe their name to having been exported to over 40 countries to control crop pests, particularly 鈥� as was the case in Australia 鈥� sugar cane pests. But their rapid dispersal across Australia meant they soon became a problem in their own right.
While studying the front line of a cane toad invasion in the Northern Territory of Australia, of the University of Sydney and his team noticed that about 10% of large adult toads had big bony lumps on their backbones.
Advertisement
Dissections revealed that the toads suffered from fused spinal joints, symptomatic of arthritis. Smaller toads did not suffer from the condition, however.
Shine explains that larger cane toads have longer legs and are able to travel further, which is why these individuals make up the front line of invasions. 鈥淭he only animals you get at the invasion front are the ones that are the descendants of the ones that went fastest, who are in turn the descendants of the ones that went fastest,鈥� he says.
Achilles鈥� heel
Ironically, this apparent advantage may put the animals at greater risk of arthritis. Larger body size and longer legs, which mean longer hops and greater impact at landing, place more stress on the toad鈥檚 skeleton. The researchers believe that the toads鈥� spines are being worn down.
Their immune systems seem to be suffering as well. Shine and his colleagues found that the toad鈥檚 arthritis was caused by a common soil bacteria called Ochrobactrum anthropi.
鈥淚t looks like the toads鈥� immune system is under such pressure that they鈥檙e actually now vulnerable to attack by these otherwise very benign bacteria. That gives us a hint that maybe the toads鈥� immune systems are a real Achilles鈥� heel that we might be able to exploit in looking for ways to control cane toads.鈥�
But sadly for Australian farmers, who fear the toads鈥� deadly toxins, they do not look about to stop their infernal progression across the country.
When the researchers raced infected toads against non-infected ones they found the former did tire more quickly. But when they then attached radio-transmitters to 22 front-line cane toads 鈥� half of which had arthritis 鈥� and released them into the wild, the infected toads travelled at least as fast as the others. On average, they advanced by 154 metres a day.
Journal reference:
