Invasive species are one of the key drivers behind the global loss of biodiversity. The cane toad (Rhinella marina) is on the 100 World's Worst Invasive Alien Species list maintained by the International Union for the Conservation of Nature (www.issg.org). This large, Neotropical toad has invaded over 40 countries worldwide and has detrimentally impacted native ecosystems in many ways. The largest, and arguably most damaging, cane toad invasion site is in Australia. There, cane toads have imperiled numerous native wildlife species through their effects as novel toxic prey items, predators of invertebrates and small vertebrates, and competitors with native frogs. This study will reveal which environmental factors and evolutionary processes are contributing to the cane toad's extraordinarily successful invasion of Australia. This knowledge will help land managers implement control measures to protect native species from cane toads, as well as potentially limit the overall extent of the invasion. Moreover, species' invasions also provide unique, albeit unfortunate, natural experiments for elucidating the processes that control species' geographic range limits. Understanding the mechanisms underlying species' range limits is a longstanding goal in the fields of ecology and evolution. It has become urgent in light of the fact that global climate change may necessitate geographic range shifts for many of the world?s species.
Cane toads are ideally-suited to investigate species' range limits because have an extraordinarily well-documented history of invasion since their deliberate introduction to Australia in 1935. In turn, this allows predictive models of their future invasion based on landscape-dispersal relationships to be validated with historical data from the actual invasion. Cane toads also have both stable and actively-expanding range edges across Australia, providing a unique opportunity to compare range limits versus expansion in geographically-replicated areas. The cane toad's invasion of Australia will be investigated using a combination of landscape genetic and genomic analyses with controlled laboratory rearing experiments. Cane toad dispersal patterns will be correlated with key landscape factors to determine which habitats restrict and/or enhance cane toad movement throughout Australia. A genomic study will also reveal putatively adaptive regions of the genome that may be contributing to the cane toad's invasion success. In combination with laboratory rearing experiments, this work will provide genotypic and phenotypic tests of the role of adaptation in a major geographic range expansion. Overall this work will provide a rare empirical test of the leading ecological and evolutionary theories for species' range limits, in addition to useful information to help control a notorious worldwide invader.
