MPIDS Colloquium: Navigation of biflagellate algae can be described accurately by an adaptive response of their flagella to light

Aquatic organisms change their direction of swimming in response to a light stimulus, in order to increase their fitness, and hence their chance of survival. This so-called “tactic” behaviour is known as phototaxis. In the laboratory we study single-cell algae which utilise this behaviour in order to satisfy their photosynthetic needs. Our understanding of phototaxis in biflagellate algae stems almost exclusively from the model species Chlamydomonas reinhardtii, via studies of its flagella, eyespot and steering. However, no comprehensive model linking all these aspects of its physiology and behaviour has been constructed and tested experimentally. In this talk, I will present a mathematical model that we have developed by coupling an adaptive flagellar photoresponse to rigid-body dynamics tailored to details of flagellar beating. We corroborate the model with experimental data -- at the flagellar and tactic levels -- to explain the accurate phototactic steering of this alga.