Local scale population risk determines the adaptive responses of larval salamanders to predator kairomones

Organisms can exhibit plasticity in phenotypic responses to environmental stimuli but the response can vary based on the evolutionary history of a population. Numerous studies have found that prey will express adaptive responses when subjected to various predators in experimental settings. For species with a large distribution, such as Ambystoma maculatum (spotted salamander), it is not surprising that phenotypic variance can be high across their range. This variance has been hypothesized to be because of different predator regimes of populations. While A. maculatum preferentially oviposit eggs in low-risk ponds (temporary fishless) to decrease egg and larval mortality, Missouri populations still use high-risk ponds (permanent with fish) for reproduction. Using a series of experiments, we investigated how A. maculatum population risk influenced adaptive responses to both native and novel predator kairomones. For natural predators, we used larval A. opacum (marbled salamanders) and Lepomis macrochirus (bluegill) and for novel predators we used Siren intermedia (lesser siren). We found that larval salamanders generally responded with no differences in morphological traits to all three predators. However, head width was larger for low-risk populations. One hypothesized benefit of larger heads (increased foraging efficiency) was not fully supported. All larval salamanders also increased refuge use with predators but this decreased over time. Our results suggest that predation risk of a population may influence the degree of phenotypic expression in response to larval predators. Overall, local adaptation may dictate the ability of prey to respond to environmental conditions within a life stage.