Back Pain in Poisonous Cane Toads
The Quick Growth of Invasive Toads in Australia
A bigger body and longer legs enable the cane toad to be a successful invader and coloniser, but success comes at a price - arthritis and back problems.
Researchers investigating the evolution of the poisonous cane toad, Bufo marinus, a rapidly spreading invasive pest in Australia, have discovered that rapid growth has a downside for the toads – spinal deformities and arthritis.
Poisonous and Successful Invader
Cane toads were introduced into the sugar cane growing state of Queensland in 1935, to combat the cane beetle, a pest of sugar cane crops.
However, as the toad is not native to Australia, it has no predators, and has since spread across most of Queensland and almost entirely across the Northern Territory, including the world-renowned wetlands of Kakadu.
Cane toads are highly poisonous at all stages of life, and as well as taking over the habitats of native reptiles, they generally poison any bird or mammal that eats them.
They are profuse in the dry southeast Queensland area and are spreading down the NSW coast. Quite a few have reached Sydney in vegetable trucks, and have established themselves at the 2000 Olympics site at Homebush Bay in Sydney's inner western suburbs, where they threaten the already-endangered Green and Golden Bell frog (litoria aurea).
Bigger Bodies Equals Bad Backs
While conducting research into the cane toad invasion front, scientists from the University of Sydney and the Department of Primary Industries found that the larger ‘invasion front’ toads were displaying a high incidence of spinal abnormalities.
“We found that around 10 per cent of toads had arthritis in their spine,” said Professor Rick Shine from the University’s School of Biological Sciences told me.
“Ironically, factors that have contributed to the toads’ rapid spread across the continent have also rendered it susceptible to arthritis.”
The researchers also observed that the process of invasion appears to have selected for larger toad body sizes on the invasion front.
“Bigger, longer legs increase their ability to seek out new territory but also puts pressure on the body with every hop,” he explained.
“Also, with much of their energy going towards movement, less is put into their immune system, which may predispose the toads towards infection with the soil bacteria that precipitate arthritis.
“Whilst the larger body size provides advantages to the coloniser, as they can move faster, eat a wider range of prey and are less vulnerable to predators, it also increase their susceptibility to arthritis,” he said.
“The major spinal deformations of these animals testify to the great stress that invading species place upon themselves, as well as upon the ecosystem they are overrunning.
"An important aspect of this research is that it highlights the importance of incorporating wildlife health perspectives in any analysis of the process of biological invasion," said Professor Shine.
The findings are published online in the Proceeding of the National Academy of Sciences, in a paper entitled ‘Invaders Under Stress: Spinal Arthritis in Invasive Cane Toads’.
