Antipredator behavior of American bullfrogs (Lithobates catesbeianus) in a novel environment

Background/Question/Methods

Invasive species must recognize potential predators to be successful in novel communities.  Individuals may retain historical predator recognition and invoke innate responses in the presence of taxonomically or ecologically similar predators, generalize antipredator responses, or learn to avoid risky species in novel environments.  Invasive amphibians in aquatic environments often use chemical cues to assess predation risk and learn to avoid novel predators via direct experience and/or associated chemical cues.  Ontogeny may also influence recognition; experience with predators may need to occur at certain developmental stages for individuals to respond correctly. We tested predator recognition in invasive American bullfrog (Lithobates catesbeianus) tadpoles that varied in experience with fish predators at the population and individual scale. 

Results/Conclusions

We found that lab-reared and wild-caught bullfrog tadpoles responded to a historical predator, Largemouth bass (Micropterus salmoides), only if the population was locally sympatric with Largemouth bass (p=0.007).  Individuals from a population that did not co-occur with Largemouth bass did not increase refuge use in response to either Largemouth bass chemical cues alone, or chemical cues with diet cues (Largemouth bass fed bullfrog tadpoles).  To test if this behavioral response was generalized across fish predators, we exposed tadpoles to Rainbow trout (Oncorhynchus mykiss) and found that tadpoles could not recognize this novel predator regardless of co-occurrence with other fish species (Friedman’s Test, X_3,4=6, p=0.1).  These results suggest that environment may be more important for predator recognition than evolutionary history for this invasive species, and individuals do not retain predator recognition or generalize across fish predators.