Australia Versus the Cane Toad: An Evolutionary Conflict.

During the year of 1935, the northern regions of Australia were facing a major pest problem: the sugar beetle also know as the Dermolepida albohirtum. The beetles were feeding on the leaves of the sugarcane plantations but the greater problem was done by the beetles larvae that hatched underground and ate the sugarcane roots resulting in either the death of most of the plants or stunting their growth. These bothered the natives of the area and they had so solve the problem. The question, however, was how?
the Greyback cane beetle Source@

After a while, they figured it out. Introduce a species that enjoyed the taste of beetles and can eat almost a truckload of them again and again. After much deliberation, the perfect predator was chosen.

The cane Toad!

That year, about three thousand (3000) young cane toads were introduced at north Queensland from Hawaii. However things did not go as planned, and the toads did not prove to be as effective a predator as the natives had hoped they would be. Why? The beetles couldn't jump as high as was needed to eat the beetles which lived at the top of the sugarcane stalks. And this then gave rise to another problem, and a war was waged between the natives of Australia, the introduced predators, and all the other predators that occupied the wild Australian north, a war that has protracted itself even to this time and from the looks of things, it seems like the natives and other predators are losing this battle . but before we delve into this battleground, let us first take a look at its prime proponent.

The Cane Toad.

a mature cane toad source @

The cane toad also knows as Rhinella Marinus is a large amphibian indigenous to South America with males ranging from 15cm to 17cm in length and females ranging up to 23cm, with a leather-like skin and lumps at the legs and back of this amphibian.
They are a very voracious species, eating anything that can fit into their small mouth, from insects to small reptiles, birds and even frogs. The cane toad is poisonous and can be lethal when eaten or threatened. It has a conspicuous gland which located at the back of its eyes which are called parotoid glands, these help the toad in secreting its venom know as bufotoxins from its wart covered leathery-like skin. These toxins are dangerous when ingested, and effectively attack the circulatory system, causing hallucinations, harsh skin reactions and are capable of causing death even in humans. They are neotropical in nature, but prefers areas mostly modified by humans such as ponds, pools and ditches. What is most distinguishing about this amphibians is their fecundity. They are capable of laying up to thirty thousand (30,000) eggs per year, and all of their offspring might survive due to a deficiency in predators of this particular species and the high toxicity of the cane tadpole which results to death of any fish or predator that eats them.

Life cycle of a Cane Toad.

Its journey begins as an egg and the rate of its growth into a tadpole is dependent on ambient temperature, as temperature increases, it chances of growing into a tadpole is over 80 percent. Within 14 hours to a week, the eggs hatch into tadpoles and the tadpoles take about four weeks to reach maturity. Because their parotoid glands do not develop until adulthood, only about 0.5 percent Of this amphibians reach adulthood.

Source @

Predators.

In their native habitat, the cane toad is preyed upon by many species such as eels, banded cat-eyed snake, the killifish, some species of catfish, and also the bullet ants.
Even oppossums prey on the toads, but with a little bit of caution.

Now we have a little insight on the cane toad, back to our war, shall we?

After the failed attempt to eliminate the sugarcane beetles using the cane toads, there originated a new problem, the cane toads themselves. Capable of giving birth to a large number of offspring within a short period of time, the cane toads began to populate Queensland at an incredible rate. But this did not bother the natives at first because they thought the natives predators such as crocodiles, quills, faunas, and snakes.

So why was this a problem?

Because the predators in Australia had not evolved to be able to resist the lethal poison of the toad, this in turn resulted in a rapid decline in animal species and the body counts begun to rise. Here and there, dead bodies of crocodiles and faunas and even snakes were uncovered and the cause of their deaths traced to the ingestion of the cane toad. An example was the northern quoll whose population reduced by 71% after the introduction of the cane toad.
a dying crocodile after trying to ingest the cane toad source@

Snake eating frogs such as the Mulga Snake, the western brown snakes, the Red-belied black snake, and even the northern death adder, a predator know its aggression and hunting skills was affected by the ecological invasion.
a dead northern death adder after ingesting the cane toad bufotoxin source@

As if it wasn't enough, the problem exacerbated to another level, and the natives began to find themselves at the other end of the battle line. The population of the cane toad was increasing geometrically, and with that increase came the deaths of the animal species that were native to the area. But, the toads were not satisfied, they needed more land, and more territory. Soon they begun to migrate into human abodes, eating pet foods and disposed refuse, taking shelter in the coolest areas of the houses which meant intrusion for the humans. The human pets were not excluded as over fifty(50) dogs died after ingesting or even biting the cane toad. A survey conducted by Surtherst in 1995 showed that by 1960, the cane toad had invaded the whole of Queensland with population increasing at the rate of over 30km per year and the northern part of the New South wales at a rate of 5km per year and even extending to the southern coast of the area and presently, cane toad have been recorded at the well inlands extending as far as the northern territory. Experts predict that of not controlled, the cane toad northern territory of new south wales, extending as far as the north west at about 60km per year. This is considered not only as an ecological invasion but a danger to other native species.

A mapped view of the cane toad population in Australia source@

Over time, predators such as the death adder and other fishes such as the catfish have evolved to avoid the cane toad, even passing the traits to their offsprings thereby contributing to the increase in population of this amphibians.

What can be done?

As a result of this ecological invasion, even the natives are slowly losing their territory to the cane toad, and their native animals as well. But all hope is not lost, Evolution has always will always come into play and it seems it will perhaps favor the natives of the Australian regions in a few years to come. New predators such as the Australian meat ants have begun to come into play, since its venom, bufotoxin primarily attacks the hearts, it is harmless against ants because ants are heartless. Yes they are. These makes them the best bet against the cane toads and experts have suggested building meat ants mould and colonies near the cane toad's breeding ponds may be an effective way to control the incursion of this species. Also, the Australian crows have evolved into using new found strategies to turn the toads to theirs belies and consume them without ingesting the toxin.

an Australian meat ant source@

So what do you think? Do the natives have a chance of winning this battle without causing more damage than they already face or will nature do what she does best and evolution might go in the favour of the toads. Nonetheless, this is currently a problem in the Australian region and even up till now, the battle line is getting longer and longer. Thank you all for reading, and once again this is aseneca reminding you to stay scientific, always.

References

Freeland, W.J. (1986). Populations of cane toad, Bufo marinus , in relation to time since colonization.
Australian Wildlife Research 13 , 321-329.

Freeland, W.J. (2004). A review of the cane toad's ( Bufo marinus Lineaus) impacts on the native Australian fauna.

Burnett, S. (1997). Colonising cane toads cause population declines in native predators: reliable anecdotal information and management implications.
Pacific Conservation Biology 3 :65-72.

Rachel cernansky (2009). Finally, a Predator to Control the Notorious Cane Toad: Meat Ants?