Assessing the potential for an evolutionary response to rapid environmental change: Invasive toads and an Australian snake

Extinctions are ultimately caused by a change in an organism's environment. Species that can adapt are more likely to persist indefinitely in the face of such changes. We argue that an understanding of the factors encouraging and/or limiting the potential for adaptation is an important consideration in assessing the long-term outcomes of environmental change. Such an approach suggests a cohesive way of assessing the potential for an impact and the long-term consequences of a particular environmental change. We illustrate this approach with a case study of a native Australian snake (the keelback, Tropidonophis mairii) faced with the invasion of an extremely toxic prey item (the cane toad, Bufo marinus). We examine the likely strength of selection, the heritability of toxin resistance and the likelihood of trade-offs or pre-adaptation. We assess an internal trade-off (between toxin resistance and locomotor performance) and an external trade-off (between resistance to the toxin of toads and a native prey species, Litoria dahlii). Our analysis reveals weak selection, high heritability and no trade-offs in resistance to toad toxin, suggesting that keelbacks are capable of mounting a rapid adaptive response to invasion by the cane toad.