A simple model and strategies for orientation in phototactic microorganisms

A simple mathematical model for the signal received by the photoreceptors of microorganisms such as <i>Chlamydomonas</i> and <i>Euglena</i> is described and used to test hypotheses for the control strategies employed by the microorganisms during phototaxis. When a suspension of <i>Euglena gracilis</i> is irradiated by two perpendicular and unpolarized beams of light, the distribution of swimming directions is bidisperse. An alternative to the Jennings-Mast shading hypothesis is proposed and shown to be consistent with this behaviour