Cane toads are a hot topic in Australia, as well as other countries that grow sugar cane. Posing a threat that can be unpleasant – or even more – these large amphibians have been the subject of much research. Almost all studies look at how to get rid of the toads. Most attempts have been unsuccessful, but it seems that the invasion may have a natural limit.
Non-native cane toads (Bufo marinus) have had a serious impact on Australia’s unique ecosystem. The 1935 introduction of toads was a bold attempt to use biological control methods. Originally a South and Central American species, cane toads were exported to sugar cane plantations in Australia, as well as Barbados, Hawaii, Brazil, and other countries. The plan was to eradicate beetle pests by introducing an effective predator, but the consequences were much broader than expected. Cane toad populations have exploded after each initial introduction. The cane toad has many advantages over native species: it is a large and voracious predator, lays many eggs at a time, and is poisonous over all life stages.
Not only have the toads failed to control cane beetles, but they now pose a significant threat to native wildlife. Their success in new environments can be measured by the expansion of their range from the original introduction in northern Queensland down to New South Wales. Over parts of the range, cane toads are advancing at about 60 kilometres each year. Native predators – and pets – are poisoned when they attempt to eat cane toads, while the tadpoles outcompete other species. Controlling the cane toad population is no small task, and currently only small areas can be cleared of toads.
Many creative solutions have been proposed, from calling in the army to sticking toads in the freezer. Some shops offer novelty items like key chains and coin purses made from toads. In fact, it seems that a less aggressive solution might be in the future. Scientists at Sydney University point out that the cane toad’s reproductive behaviour might play a role. So far, larger and faster toads have done the bulk of the breeding as the population spreads. After generations of such selective mating, the resulting offspring have evolved some problems – arthritis and a back back.
In fact, in their native habitat, the large cane toad has no reason to move quickly. But in Australia, where groups move rapidly across the terrain – going 10 metres (30 feet) overnight – the leaders of the pack may move much faster – up to one kilometre over the same period. These faster individuals sport a modified body shape with bigger front legs and longer backs, as well as showing some physiological changes. Rapid adaptation over such a short timescale has had an unbalanced effect and about 10 percent of toads develop spinal arthritis. Immune function may also be compromised, as soil bacteria are associated with arthritis development in this species.
The hope is that the physical changes will have effects on both the population’s size and the speed with which the toads are invading new areas. If the advance could be slowed, other preventive measures might be more successful. At the very least, containing the cane toad problem would benefit Australia’s endemic and unique wildlife species.
Photo credit: antheap@Flickr.com
