Evolution of chemical-cue-mediated antipredator behavior in threespine stickleback populations experiencing northern pike predation

Human-mediated environmental challenges are severely impacting local and global levels of biodiversity. Phenotypic plasticity can play a major role in aiding population persistence because plasticity can buffer populations from novel challenges. Given this role, it is possible for the degree of plasticity to evolve rapidly as it may place phenotypes near, but not exactly on, an adaptive peak for the new environment. Here, we asked if behavioral plasticity evolves following the introduction of a novel predator. We measured behavioral responses of threespine stickleback (Gasterosteus aculeatus) populations, with and without the introduced apex predator northern pike (Esox lucius), to three different chemical odors, (1) conspecific alarm odors, (2) digested odors, and (3) pheromones of northern pike (pike odor). We demonstrated that stickleback from pike-invaded populations do not respond to any of the treatments in our study, while stickleback from pike-free populations behaviorally respond to the presence of alarm odors but not digested or pike-specific pheromones. Our results provide evidence that the behavioral plasticity of stickleback populations can rapidly evolve to the presence of northern pike, and more importantly, that this response is consistent across multiple populations.