Bars in each graphic represent mean values and standard errors. Statistical comparisons are indicated by the arrows; ns: non-significant; ∗p < 0.05; ∗∗p < 0.01; ∗∗∗p < 0.001; ∗∗∗∗p < 0.0001. Comparisons were done by the Mann-Whitney U test followed by correction for multiple comparisons.