FIGURE 4:

Strain energy applied by a tandem pair is quasiperiodic. (A) Quasiperiodic oscillations over 270 s of the total strain energy (U_s) imparted by a representative wild-type tandem pair. (B) Boxplots for eight pairs of the period of the oscillations of U_s, T_Us. Circles represent outliers, and the notched section of the boxplots shows the 95% confidence interval around the median (Wilcoxon–Mann–Whitney test). (C) Phase-average traction stress maps (nanonewtons/unit area) in the pair-based reference frame for Ax2 wild-type pairs (N = 14). The splitting into phases is performed using U_s(t). Each column corresponds to a different phase. First and second rows show the magnitude of the total and axial stresses, respectively, for each phase. Front (F) and back (B) of the pairs are indicated. Blue arrows indicate the mean net axial force generated by each cell of the pair, assuming the contact line between cells is in the middle of the pair. Purple and cyan arrows indicate the mean force exerted by the leading cell on the trailing cell and vice versa. Phase-average duration (T), speed (V), DOC between the pair’s cells, and pair length (L; see also Supplemental Figure S3).