(Image via australiangeographic.com)
Staff Writer: Emma Bowser
Email: ebowser@umassd.edu
Cane toads (Rhinella marina) are considered by conservationists to be one of the worst invasive species in the world. Because a large portion of their diet consists of insects, this species has been introduced to countries like Australia in hopes that they would be able to reduce insect populations.
In 1935, sugarcane plantation owners convinced the Australian government to import 2,400 cane toads specifically to combat cane beetles, which eat the roots of sugarcane plants.
However, this plan was not successful because the toads were unable to meet expectations and ended up rapidly reproducing throughout the local environment instead. The current estimate of the Australian cane toad population is approximately 200 million.
National Geographic reports that in addition to Australia, “cane toads have spread in Florida, Hawaii, Guam, the Philippines, the Caribbean islands, the western Pacific islands, Papua New Guinea, and elsewhere.”
Even though their diet is primarily insects, cane toads will also eat “small birds, other reptiles and amphibians, and small mammals” and some vegetation. When other food is not available, they will eat food intended for pets and humans, so people who live in urban areas that are known to have cane toads are advised to keep food inside and sealed away from any toads.
Most programs that aim to reduce the cane toad population involve humane euthanasia because the toads secrete a toxin called bufotoxin that affects the cardiovascular system and causes hallucinations.
Tadpoles can be caught in traps specifically designed to lure them in with pheromones. This works because, according to Watergum, “cane toad tadpoles are instinctively drawn to and consume other cane toad eggs, as a means to reduce competition and seek nutrients.”
You can watch a video explaining this process here.
Dr. Rick Shine has helped establish programs to reduce cane toad populations in Australia by involving groups like the Australian Research Council and local communities. Because of this, many places in Australia now hold toad-busting events where people capture and euthanize toads and tadpoles. It’s estimated that several million toads and tadpoles have been euthanized because of these events.
The main problem with toad-busting is that it requires people’s time and energy. The toads and tadpoles have to be caught or captured and then properly euthanized and disposed of so that native predators don’t eat the remains and die.
Australian Geographic also points out that “a single clutch can contain more than 30,000 eggs, so even if you catch and kill 99 percent of the offspring, there will always be some that make it to adulthood.”
To address this issue, Shine has taken advantage of the same thing that the tadpole traps do—the natural cannibalistic instincts of the species. One of the biggest reasons why this works is because cane toad tadpoles don’t eat other species of tadpoles, and they don’t produce toxins in this stage of life.
It’s the perfect time for them to be eaten.
The issue that Shine ran into is the fact that tadpoles, like all babies, eventually mature and become adults. His solution to that is to use CRISPR to block the metamorphic process, locking the tadpoles into a state of eternal youth like Peter Pan.
Shine and his team started small by using CRISPR to block out the part of cane toads’ DNA that causes pigmentation to occur. This resulted in tadpoles that had albinism that remained through the metamorphic process, proving that this method would be permanent.