Who rules the world? Toads.

Using organisms to control for pests is a type of biocontrol. While there have been many success stories, there are also cases gone wrong. An example of a biocontrol gone wrong is the introduction of Cane toads (Rhinella marina) to Australian farmlands.  Following its introduction the toad began spreading, and continues to do so, throughout Australia and other countries. When introduced to a new area animals face novel predators, which may alter the prey morphology, behavior, and physiology.  The cane toad has shown rule over the predators it faces, as it’s poison glands kill the native predators that are unfamiliar with it’s anti-predatory behavior. Can a toad really be on it’s way to a invading an entire continent?

Researchers at the University of Sydney sought out to determine if the same animals but in different places respond the same way to predators. Previously cane toads had been introduced to French Guiana and Hawai’i, and in 1935 to Australia.  Each place is very different in environment and variability of predators. They also investigated how size and morphology might impact anti-predator behavior.  Finally they assessed the role of developmental plasticity, for example the environment in which they were raised, on anti-predator tactics and whether these behaviors were heritable. To examine these scenarios the researchers collected toads from the different locations. A “common garden” breeding experiment was done on the toads collected from the two extremes of invaded Australian land. Common garden experiments place organisms from different environments into one, or a common environment. All captured toads underwent trials of predator responses. Toads were placed at the beginning of a race way, and poked in their urostyle to encourage hoping. Frogs from Australia were less reluctant to hop compared to French Guiana and Hawai’i. Across countries, frogs with longer legs were less reluctant to hop. Interestingly, the toads at the invasion front of Australia were more reluctant to hop, than those closer to the initial introduction. The similar results were seen in their offspring. The toads from the common garden experiment were more likely to exude toxin.

Overall, biological invasion of the cane toad has allowed scientists to investigate evolutionary shifts in anti-predator responses of the cane toad. Understanding the behavior, morphological and physiological changes that follow novel colonization is important for gaining insights on how to control invasive species . It can also lead to understanding future nature-human interactions as urbanization increases and more wild animals have to adapt to this new environment.  

Hudson, C. M., Brown, G. P., & Shine, R. (2017). Evolutionary shifts in anti-predator responses of invasive cane toads (Rhinella marina). Behavioral Ecology And Sociobiology, 71