Fig. 5.

Environmental adaptability of the Ray sperm in viscous solutions. Images (A–D), trajectories (E), and velocities (F) of the Ray sperm swimming in four types of solutions (normal solution, viscous solution i, viscous solution ii, and viscous solution iii) observed through the bright-field microscope. Box: 25th to 75th percentiles, whisker: 10th to 90th percentiles, and horizontal line: median value. Since highly viscous solutions hindered the helical motion of soft material, the tail twined as a circle and almost made no contribution to the propulsive force. The forward velocity in viscous solution i was 28% slower than that in normal solution. (G) Rotational speed and propulsive force in four solutions (n > 34). Bar = mean; error bar = SD. The high viscosity of solutions reduced the rotation of the head and abolished the helical rotation of the tail. (H) Fitting relationships between the rotational speed of the head and forward speed (mean ± SD) in different solutions, showing the rotational speed of the head was correlated with the forward speed positively.