Using pheromonal cues to control invasive cane toads (Rhinella marina) in Australia

Abstract

Cane toads, Rhinella marina, were brought to Australia in 1935. The toads spread rapidly, and currently are found over more than 1.2 million km2 of tropical and sub-tropical Australia. Cane toads have had devastating impacts on Australian wildlife, largely due to the vulnerability of predators to the toads’ toxins. As toads continue to spread, we urgently need to develop management strategies to reduce the impact of toads on native fauna. Two new aquatic-based methods of cane toad control show great promise. First, traps that exploit the chemical attraction of toad tadpoles to conspecific eggs (a cannibalistic response) can be used to remove toad tadpoles from waterbodies. Secondly, a ‘suppression cue’ involves the suppression of toad eggs and hatchlings by older conspecific tadpoles. Although both strategies work well under lab conditions, unanswered questions include how the mechanisms function under different environmental conditions, how chemical cues interact, and the feasibility of using these methodologies in the field. My thesis addresses these questions. I ran extensive lab-based tadpole trapping trials to investigate how the effectiveness of trapping is altered by factors such as temperature, tadpole developmental stage, and toxin and tadpole geographic origin. I investigated whether exposure to one chemical cue affects the response of tadpoles to other cues, and I ran mesocosm trials to determine whether removing some (but not all) of the cane toad tadpoles from a waterbody increases the viability of survivors. To determine whether ‘suppression’ can successfully be transferred to the field, I ran trials in field ponds. Finally, I investigated the way in which cane toads are able to invade areas that are theoretically considered ‘too cold’ for the species to persist. My thesis documents the ways in which the success of aquatic-based cane toad control methodologies can be maximised, and how lab-based trials might translate into effective field practices.