Fig. 9. Correlation coefficients between the independent contrasts in hovering flight mass-specific metabolic rate and the activity of (A) hexokinase (HK), (B) cytochrome c oxidase (COX) and (C) glycogen phosphorylase (GP). The distribution of correlation coefficients results from analyses performed with 10 000 different trees (see Materials and methods). The correlation coefficient obtained from cyt b sequence information using a gradual (solid lines) and speciational (broken lines) model of evolution are presented for HK (gradual: r=0.77, P=0.004; speciational: r=0.71, P=0.010), COX (gradual: r=0.35, P=0.27; speciational: r=0.43, P=0.16) and GP (gradual: r=0.53, P=0.07; speciational: r=0.67, P=0.02). The shaded areas represent non-significant relationships, given that the critical values of the correlation coefficient r for significance at the P=0.05 level (two-tailed) is 0.576 (d.f.=10).