Behavioral flexibility, as a facet of cognition, occurs when an animal switches from a previously successful behavior to a new behavior when the environment changes. For example, an animal might start using a new foraging site when an old food site is no longer profitable. Behavioral flexibility might be especially important for animals in rapidly changing environments as it allows individuals to identify new successful behavior patterns under novel conditions. In my dissertation, I focused on questions related to the mechanisms that drive and maintain intraspecific variation in cognition, with a focus on behavioral flexibility. Using the threespined stickleback as a model, I studied intraspecific variation in cognition from four different angles. First, I tested the hypothesis that sticklebacks from populations inhabiting different environments may be primed to use different cues within novel learning conditions. When individuals from two populations were trained on a color vs. spatial discrimination task, the two populations excelled on different tasks, and I discuss how ecological factors might be tied to this variation. Second, I tested the hypothesis that individual differences in behavioral flexibility is part of an overall suite of traits related to reactivity to changes in the environment. I found that individuals that showed a higher cortisol stress response and that were more reactive to a predatory threat were slower to learn a novel discrimination task, but not necessarily faster to respond when learning conditions changed. Third, I explored the underlying causes of variation in behavioral flexibility by asking whether individual differences in reversal learning performance were more strongly associated with variation in neophobia or inhibitory control. I found that early performance on reversal learning trials was associated with behaviors across contexts, while time to criterion during reversal learning was independent of other behaviors. Finally, I took advantage of the adaptive radiation of sticklebacks to ask how cognition-related behaviors might evolve as populations colonize new environments. Using a common garden design, I found extensive population-level variation in behaviors related to behavioral flexibility suggesting that these behaviors have evolved as populations invaded freshwater environments. Altogether these studies contribute to our growing understanding of behavioral flexibility by highlighting the wide range of both intra- and inter-population variation and further elucidating the mechanisms that may drive the maintenance of this variation.
