While cane toads are evolving with incredible
rapidity as they spread across Australia, they are
paying for increased speed with painful arthritis.
Image: Istockphoto

Survival of the ‘fittest’ is proving to be a double-edged sword for Australia's cane toad, according to University of Sydney professor of evolutionary biology Richard Shine, speaking at the recent annual Ecological Society of Australia conference in Sydney.

The Australian Research Council Federation Fellow said in the space of 70 years the introduced pest has evolved into a bigger and faster animal than the smaller, slower moving toads introduced to Queensland in the 1930s.
 
Those toads moved an average of 10m overnight. The ones at the leading edge of the advancing front, now at the WA-Northern Territory border crossing into WA, are now 10 times as fast and can move up to one kilometre on a wet night.

However, bigger and faster is not always better. Professor Shine said the evolutionary success of the pest was taking its toll, with arthritis identified in the spinal columns of toads at the front of the invasion wave.

"Toads that run at the front of the pack are becoming bigger and faster," Professor Shine said.

"They have different personalities, different shapes and are developing different physiologies."

Professor Shine said the bigger and faster toads at the ‘invasion front’ were producing faster moving babies with bigger front legs and longer back legs - what researchers call the ‘Olympic Village Effect’.

However there is a downside for Bufo marinus - skeletal deformity caused by its rapid evolution.

"We are seeing toads in the Northern Territory with spinal arthritis - big, bony lumps on their spine," he said.

"This is something that has never been seen before in other amphibians."

Surprisingly, the toads continue their advance despite the pain caused by the bone deformities.

Professor Shine said a better understanding of cane toad biology could help researchers lessen the impact on the flora and fauna of Australia.

"We used to focus our attention on controlling cane toads without understanding how they work.”

Professor Shine said researchers have discovered a chemical released by the cane toads when they are frightened or alarmed.

This ‘alarm pheromone’ is extremely useful for controlling tadpoles as the ones that do not die from the pheromone grow to be much smaller. They also have found a toad lungworm parasite particularly effective for killing baby toads.

"The great news is the pheromones and lungworm parasite do not affect Australian frogs," he said.

"We have one biological control that kills tadpoles and others that are useful against baby toads.

"Taken together, we have a powerful set of methods for controlling cane toads from an early stage."

Professor Shine's research group also is exploring how some Australian predators have adapted to surviving the cane toad's poison.