Statistical analysis
All analyses were conducted in R v.4.0.2 (R Core Team 2020). We tested the effect of habitat on overall brain volume using a linear model with habitat (categorical variable: lake, stream, hatchery), fork length, and their interaction. Effect of habitat on brain regions was tested by linear models with habitat and total brain volume minus the volume of the region of interest (Pike et al. 2018), and their interaction. Variables in all models were log-transformed. Non-significant interaction terms were removed from models. Significance of the explanatory variables was evaluated using ANOVA tables using Type II and III sums of squares for models without and with the interaction term, respectively. Model fit was diagnosed by control of distribution of model residuals and association of fitted and residual values. Differences between categories of habitat were analyzed using Tukey’s HSD post-hoc test.