Fig. 6. Effects of fluid shear on sperm swim speed and direction. The mean direction of swimming is expressed in a circular coordinate system (see Table 2 and text for details). (A) Sperm swimming trajectory as evaluated with respect to the nearest egg surface. The unit vector length (r) is described as a function of log-shear, using least-squares regression to identify the best fits (live sperm, abalone eggs: y=–0.20log₁₀(x)+0.53, r²=0.91, F_1,5=30.5, P<0.01; live sperm, brine shrimp eggs: y=0.03log₁₀(x)+0.16, r²=0.53, F_1,5=4.63, P=0.10; dead sperm, abalone eggs: y=0.008log₁₀(x)+0.17, r²=0.09, F_1,5=0.40, P=0.55). (B) Sperm swimming trajectory is evaluated as in A, but with the origin facing directly into flow (live sperm, abalone eggs: y=0.15log₁₀(x)+0.47, r²=0.92, F_1,5=52.35, P<0.01; live sperm, brine shrimp eggs: y=0.19log₁₀(x)+0.52, r²=0.90, F_1,5=36.26, P<0.01; dead sperm, abalone eggs: y=0.001log₁₀(x)+0.95, r²=0.03, F_1,5=0.14, P=0.72). (C) Translational swimming speeds of sperm (live sperm, abalone eggs: y=47.6–7.8log₁₀(x), r²=0.44, F_1,199=48.4, P<0.001; live sperm, brine shrimp eggs: y=34.–0.6log₁₀(x), r²=0.04, F_1,119=0.44, P=0.49; dead sperm, abalone eggs: y=0.67–0.003log₁₀(x), r²<0.01, F_1,118=0.004, P=0.95). Each symbol is a mean ± s.e.m.; error bars are smaller than symbol sizes in some cases.