Professor Rick Shine of Sydney University recently won the Prime Minister's Science Prize for research into helping northern Australia's peak predators to survive the cane toad invasion.
Cane toads were introduced to the north Queensland sugar cane area in
the 1930s in the mistaken belief that they would eradicate the cane
beetle. Since then they have been steadily spreading south and west. To
the west they have moved across the Queensland savanna into top end of the
Northern Territory ( including into Kakadu National Park) and further
west into the Kimberley region in the north of Western Australia.
Cane toads (Rhinella marina) are poisonous through their life cycle.
As these introduced pests advanced, they brought devastation to native wildlife
which sought to prey on them in the areas they have colonised. Goannas,
snakes, freshwater crocodiles, quolls and dingoes are some of the native
species which have died as a result of the toad's poison. It has
been estimated that up to 95% of native predators have been killed as this
introduced pest moves westward.
Professor Shine became an expert on cane toads while he was researching
snakes on the Adelaide River floodplain south of Darwin in the Northern
Territory. The frontline of the cane toad invasion consists of large, highly
toxic adult males. They are so toxic
that a meal of one toad is sufficient to kill a Yellow-spotted Monitor, a goanna.
In his research Professor Shine has been dropping juvenile toads ahead of
the invasion line. When the native
predators eat these they get sick but do not die as the juveniles are less
toxic. As a result they are less likely
to prey on the larger toads when they arrive.
Initial studies have shown mortality rates dropping below 50% among goannas after the toads arrive.
The professor has further developed his theories working with Dr Ben
Phillips at the University of Melbourne. They have discovered a genetic
variation in toads that governs how quickly they spread.
“Genes that make a toad go faster move to the front,” Professor Shine
said. “The genes that say ‘take a night
off’ stay at the back.”
By dropping slower dispersal juveniles ahead of the fast moving frontline,
the professor is not only training predators not to eat the larger, deadly
toads but is creating a “genetic backburn” to slow down the advance.