How Researchers Trained Australian Monitor Lizards To Avoid Toxic Toads

Australia is home to some of the world's deadliest animals. However, few are as dangerous as the cane toad. Native to Central and South America, the innocent looking amphibian is an invasive species that was imported to Australia in 1935 to control the native grey-backed cane beetles that were harming sugarcane crops. With very few natural predators their population began to grow rapidly. Experts estimate that there are currently over 200 million specimens spread across Northern Australia, and the numbers are only growing.

The increasing population is proving to be deadly for many native Australian animal species that prey on the toads. That's because when the amphibians sense danger, they release a milky substance called bufadienolides that is so toxic that it kills the predator almost instantly.

While some animals have learned to avoid the frogs altogether or attack its belly and eat only the mildly toxic internal organs, the Australian monitor lizards or goannas as they are called continue to be very susceptible. The primarily carnivorous lizards that prey upon small animals are notorious for snaring these toxic amphibians. Unfortunately, in most cases, it turns out to be their last meal since it takes the cane toad less than 30 seconds to release enough poison to kill the reptile. Not surprisingly, the population of goannas that not only feature prominently in the Aboriginal culture but also, play an important ecological role, has dwindled drastically.

After extensive efforts to curb the toad's population growth failed, a team of researchers led by Georgia Ward-Fear, a Ph.D. student at the University of Sydney came up with an innovative plan. They decided to train the reptiles to avoid the cane toads! To implement the idea they went to a remote floodplain in the Kimberley region of northwestern Australia, that had not yet been invaded by the amphibians and fed the wild lizards, juvenile cane toads. Though the smaller animals release the same toxin as the adults, they do so in smaller doses. Hence, while the poison does make the reptiles sick, it does not kill them. The researchers say it took just one or two trials to teach the smart lizards to avoid cane toads altogether.

What was encouraging is that they continued to avoid the animals even when the larger cane toads arrived. The scientists say that eighteen months after the study started most of the trained lizards are still alive, while those that had not been exposed to the small toads continue to succumb to their poison.

The researchers who published their study in the Biology Letters journal on January 6, say releasing small frogs in areas that have still not been invaded by the dangerous amphibians can help curb the alarming decrease in the population of the wild lizards. They also believe that the success of the study will lead to "a new and safer way to conserve wildlife population by giving the predators a chance to learn rather than to die."

Resources: phys.org,royalsocietypublishing.org, popsci.com,sydney.edu.au, Department of Environment and Conservation, Western Australia