Introduced to Australia, the cane toad evolved to eat its own kind

Exposure to the cane toad's own toxin causes the tadpoles to eat eggs or smaller fellows.

According to the NYT, cane toads are native to Central and South America. Here, people have never been discovered that they cannibalize their own kind. However, this behavior changed when the toad was introduced to Australia.

For decades, scientists have witnessed cane tadpoles eat eggs or smaller tadpoles. The cause of this cannibalism is still a mystery.

Cane toad, native to South America and Central America.

A new study, published this month in the journal Ecology and Evolution, shows that Australian cane toad tadpoles experience heightened appetite stimulation when they are exposed to a toxin found in cane toad eggs. This is also the toxin that makes this toad venomous in its body.

Cane toads, native to South and Central America, were introduced to Australia by scientists in 1935 in the hope that they would reduce the number of cane beetles, which were causing problems for sugarcane farmers in Australia. Australia. With their prey in abundance and no predator able to withstand their poison, the toads quickly proliferated into the tens of millions. From there, they became invasive, causing native amphibians to be excluded from their Australian habitat.

However, the cane toad itself also had some changes when it was migrated to Australia. These phylogenetic behaviors were not seen in the cane toads of South and Central America. It has only begun to be observed across Australia in recent decades. These behaviors have developed throughout the cane toad community in Australia.

Jayna DeVore, a postdoctoral researcher at the University of Sydney and the study's author, said: 'This is a unique case where evolution is incredibly rapid and we can see it. it happens in real time'.

More than a decade ago, scientists in Australia, including Michael Crossland, a researcher at the University of Sydney and the study's author, studied the effects of cane toads on native frogs. land. They accidentally discovered that these tadpoles love to eat cane toad eggs, they still flock to find cane toad eggs even though they provide them with eggs of other amphibians.

 The hatching process causes tadpoles to show a craving for cannibalism.

It prompted Dr. Crossland to conduct a series of experiments to better understand the phenomenon. Last year, he and his colleague Richard Shine, a biologist at Macquarie University, demonstrated that the tadpoles of the cane toad are attracted to chemical compounds associated with the eggs and young of the cane toad.

These eggs are chemically similar to the eggs of other amphibians, but with one important difference: They contain bufadienolide, the same chemical that makes cane toads poisonous and protects them from predators. The researchers suspect that it is this chemical that triggers the tadpoles to eat younger members of their species.

In their latest study, the scientists bred wild cane toads, put the tadpoles in tanks with varying amounts of the toxin bufadienolide in the water, and fed them eggs of cane toads and Australian frogs. Tadpoles not exposed to bufadienolide toxin barely eat toad and frog eggs. However, the tadpoles that were exposed to bufadienolide toxin ate both native frog eggs and those of their own kind with gusto.

Scientists also study tadpoles while they are hatching. They found that hatching caused tadpoles to exhibit cannibalistic cravings similar to when bufadienolide was added to their water. That suggests that the toxins in the eggs are released into the water when the tadpoles hatch.

May have evolved this response to their own poison.

Matthew Greenlees, a cane toad expert and postdoctoral researcher at Monash University, who was not involved in the study, said: 'We've known for a long time that they cannibals, but the new discovery helps. explain the mechanism of this problem'.

The study's authors suggest that Australian cane toads may have evolved this response to their own toxins to reduce the number of cane toads that breed in the environment.

Dr Crossland said: 'It is well known that toad tadpoles in Australia are very competitive with each other. Cane toad densities are much greater in Australia than in their native areas and under high densities, cannibalism is likely to develop. They're basically figuring out how to get rid of future competitors."

Dr Crossland said the fact that cane toads were able to develop cannibalism in such a short time was 'incredible'. He said: 'Toads only came to Australia in 1935. It was a very fast evolution'.

Invasive species tend to evolve more rapidly than native species, partly because they reproduce rapidly. This allows scientists to track evolution over decades, as opposed to centuries or millennia in native species.

In their next study, they plan to test how cane toads are evolving to defend themselves against their cannibals. Dr DeVore said: 'It's really an arms race between the cannibal tadpoles and the young.