Figure 3

Both productive and non-productive rolling generate optical signals. (A) Tracking the centroid of the head of a resting sperm in Ca²⁺-deficient medium HS0Ca. Heavy lines indicate orientation during the t = 1 to 2 s (frames 300 to 600) and 2 to 3 s (frames 600 to 900) segments that are analyzed in panels B and C. (B, C) Sinusoidal variation of intensity of centroid region-of-interest (ROI; green) regularly peaks near transitions between right cheek (RCh) and left cheek (LCh) orientation. In C, the centroid intensity peak at approximately t = 2.4 s (around frame 720) occurs without a transition in orientation. (D) ROI intensities during the indicated segment (frames 701 to 811, dashed lines in C, circled in panel A). The left bar of each pair is from frames 701 to 751, the right bar from frames 761 to 811. Blue, red, and gray indicate LCh, RCh, and indeterminate cell orientations. (E) Stop-motion images of the same cell at the indicated frames, occurring without (abortive, above) or with (productive, below) changes in cell orientation. The cartoon indicates how an observer facing the oncoming sperm would see the plane of the head roll in a counter-clockwise direction as indicated by the green hour-hand.