Mitochondrial respiration rate (VO
) of mouse and zebra finch erythrocytes normalized by the protein content of the cell suspension. White bars represent baseline respiration rate (on glutamate-malate). Grey bars represent respiration rate after the inhibition of complex I (amytal), which is reversed by the addition of succinate (black bars) in zebra finch. Letters indicate significant differences between groups according to GEE Bonferroni post-hoc (N = 7 per species for each treatment).