Fig. 2
A Principal component analysis (PCA) score plot. Three groups are distinguished: high altitude, blue boxes; low altitude, red circles; and quality control (QC) samples, purple diamond. B Orthogonal projection to latent structures discriminant analysis (OPLS-DA) scores plot, showing two groups: high altitude (blue) and low altitude (red). R2 examines the goodness of fit whereas Q2 evaluates the predictive ability of the model. C Permutation tests for the corresponding OPLS-DA model. D Volcano plot showing relative changes in liver metabolites between high and low altitudes. Red circles represent metabolites that are in higher concentrations in liver of high-altitude lizards, as compared with low-altitude animals, whereas blue circles represent metabolites that are present in lower amounts in high-altitude lizards