Fig. 7.

The phototactic ability decreases dramatically as ω_r is reduced by increasing the viscosity. Results from three representative populations are shown with distinct colors. Each data point represents the average phototactic ability of the population at a given viscosity. Horizontal error bars are standard deviations, whereas vertical error bars indicate the range of population mean values, when it is computed from 100 random selections of 0.1% of the data. A blue continuous line indicates the prediction of the full hydrodynamic model; the red line is obtained from the reduced model. (Inset) α(t) from the full and reduced model at the lowest viscosity.