The Tale of the Cane Toad
This week Karen Samis, Assistant Professor in the Biology Department at UPEI, shares a fascinating story that shows the plasticity of invasives and the organisms that are affected by their introduction.
This is not a new story (nor a PEI one), but I think it serves as a good lesson for how careful we must be when making attempts to manage habitats and species. It is also a great example of the power of species to adapt to new environments – and, in some ways shows how invasive species can be rather fascinating creatures.
Cane toads (Bufo marinus) were purposely introduced to Australia in the early 1900s as a (failed) attempt to control a beetle problem. With the opportunity to establish new territory ahead of them, the race was on to colonize a larger area than the toads were originally introduced to. How best to colonize new lands rapidly when you’re a toad? Yes – make lots of eggs, which cane toads do very well in comparison to native Australian toads, but another answer is to grow longer legs. Leg measurement on toads across generations have shown that toads with longer legs than their first introduced ancestors lived a great life beyond the reach of human managers and succeeded in expanding the species’ range. In other words, toads with longer legs hopped further and faster than toads with shorter legs, and now the entire population has longer legs, on average, then their ancestors in their North American home range.
But there is more to this story. Cane toads are also highly toxic and have few predators. Many potential Australian predators have learned not to prey on these toads, including snakes. But, some species of snake have changed their physique and their eating habits in response to living with these toxic toads. Because snakes can only eat what their mouth can engulf, snakes with large mouths (large headed relative to their body size) are more likely to consume more toxins than their body can handle and die after eating a cane toad. What’s the answer? – eat smaller toads! Researchers have found that some species of Australian snakes have evolved to have smaller heads (smaller gapes and larger bodies than the same species had when the cane toads were introduced) thereby making it less likely they will consume more toxin than they can handle, and more likely to survive their toad lunch. Now if only those snakes could eat a few more toads…