Adjusting to a toxic invader: native Australian frogs learn not to prey on cane toads

Biological invasions provide opportunities to study novel behavioral interactions between predators and their prey. To withstand detrimental effects from a potentially lethal invader, a native taxon must somehow adjust to the invader's presence. Cane toads (Bufo marinus) are highly toxic to native Australian anurans and constitute a major threat if consumed. We recorded the responses of Australian marbled frogs (Limnodynastes convexiusculus) during their first encounters with edible-sized cane toads. The frogs exhibited rapid avoidance learning: toad-exposed frogs were less likely to attack subsequently encountered cane toads (and hence more likely to survive). Among-clutch variance in learning rates and in physiological tolerance to toad toxins was low, suggesting that genetically based adaptive changes to frog feeding responses will be slow (especially given that rapid learning reduces mortality and thus reduces the fitness decrement of initial willingness to attack a toad). Hence, rapid taste aversion learning is the primary mechanism enabling marbled frogs to persist in the presence of a potentially fatal invader. In combination with previous work, our study shows that some native predators adjust to the threat posed by cane toad invasion via taste aversion learning, whereas others show genetically based modification of feeding responses. More generally, both learning and adaptation enable vulnerable native taxa to survive the arrival of a toxic invasive species.