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.