Survival benefits and divergence of predator-induced behavior between pumpkinseed sunfish ecomorphs

Abstract

Resource use is widely thought to influence adaptive phenotypic divergence, whereas other ecological factors, such as predation, are frequently overlooked, particularly in studies of polyphenism in fishes. Juvenile pumpkinseed sunfish (Lepomis gibbosus) reared with predatory walleye (Sander vitreus) increase body depth and dorsal spine length, indicating that developmental responses to predation can shape phenotype. Body form responses to the same predator cues though have also evolutionarily diverged between sunfish ecomorphs that coexist in single lake populations by inhabiting either littoral or pelagic habitats, suggesting that predation risk varies between habitats. Here, we test if prior exposure to predator cues influences the development of behavior in juvenile pumpkinseed sunfish, if behavioral responses to the same predator cues vary between ecomorphs, and if induced phenotypic variation affects survival under predation. Behavior depended strongly on prior exposure to predator cues, but this effect varied between sunfish ecomorphs, indicating that ecomorphs have different responses to the same predator cues. Predator-induced phenotypes had higher survival than control phenotypes under simulated littoral but not pelagic conditions. Predator-induced phenotypic responses are candidate-inducible defenses, and divergent responses between ecomorphs suggest that they can evolve in response to selection imposed by differences in habitat-specific predation risk.