Fig. 3.

Photoresponse frequency dependence and colony rotation. (A) The normalized flagellar photoresponse for different frequencies of sinusoidal stimulation, with minimal and maximal light intensities of 1 and 20 μmol PAR photons m^-2 s^-1 (Blue Circles). The theoretical response function (Eq. 5, Red Line) shows quantitative agreement, using τ_r and τ_a from Fig. 2B for 16 μmol PAR photons m^-2 s^-1. (B) The rotation frequency ω_r of V. carteri as a function of colony radius R. The highly phototactic organisms for which photoresponses were measured fall within the range of R indicated by the purple box, and the distribution of R can be transformed into an approximate probability distribution function (PDF) of ω_r (Inset), by using the noisy curve of ω_r(R). The purple box in A marks the range of ω_r in this PDF (green line indicates the mean), showing that the response time scales and colony rotation frequency are mutually optimized to maximize the photoresponse.