Sophisticated early life lessons: threat-sensitive generalization of predator recognition by embryonic amphibians

The ability to develop effective antipredator responses early in life should be strongly promoted by natural selection. Recent work has shown that embryonic amphibians can learn to recognize predators even before they hatch. Here, we showed that embryonic woodfrogs, Rana sylvatica, learned the danger level associated with a predator prior to hatching and generalized their learned recognition to other similar predators with which the woodfrogs lacked experience. Embryos exposed to salamander odor (SO) paired with injured tadpole cues learned to recognize the salamander Ambystoma tigrinum, but those exposed to SO paired with well water did not. When we increased the concentration of alarm cues to which embryos were exposed, tadpoles showed stronger response to salamander cues. In addition, the tadpoles generalize their learned response to the odor of closely related newts Cynops pyrrhogaster but not Xenopus frogs. In accordance with the Predator Recognition Continuum Hypothesis, the ability to generalize was dependent on the threat level of the predator. Our results highlight the sophistication of learned responses to predators by embryonic amphibians and stress the need for studies in other taxa.