Sperm chemotaxis in marine species is optimal at physiological flow rates according theory of filament surfing
Fig 2
Sperm-egg-encounter probability displays maximum as function of shear rate in simulations for sea urchin sperm at physiological flow rates.
Probability Psperm:egg(α) that a single sperm cell finds an egg as function of external shear rate α. Simulations account for flow-induced distortion of concentration fields into long filaments as well as convection and co-rotation of sperm cells by the flow (green triangles, mean ± SD). Without co-rotation results change only marginally (blue circles). Simulation results agree with predictions from our theory of filament surfing (red, presented below). Without sperm chemotaxis, the encounter probability is virtually zero (<10−5, black). Our theory has a single fit parameter, the flux of sperm cells arriving at the filament, jout = 0.063 m−2s−1. This value matches in magnitude the limit jout = ρegg vh/4 = 0.04 m−2s−1 for a ballistic swimmer with random initial conditions, see Sec E in S1 Text for details. Parameters as in Fig 1B.