Sensorimotor processing and navigation in confined microswimmers

All living organisms are environmentally intelligent. This is the fundamental distinction between life, and other forms of matter. Even unicellular organisms are capable of complex behaviours, for they can sense as well as respond to changes in the environment. Here, we study spontaneous and constrained motor actions in algal microswimmers, using motility as a dynamic read-out of behaviour and physiology. Previous studies have focussed on locomotion transients over short timescales ranging from milliseconds to minutes. We present a novel microfluidic platform which allowed us for the first time to monitor and analyse algal cell motility over hours, and even developmental timescales. We focus on two species, a biflagellate which exhibits a form of run-and-tumble, and an octoflagellate which exhibits a tripartite behavioural repertoire termed run-stop-shock. Excitability and stochastic transitions in swimming gait are projected onto a low-dimensional state space. We reveal how flagellar mechanosensitivity mediates repetitive boundary interactions, and discuss the discovery of a light-dependent quiescent regime. Finally, we conduct pharmacological perturbations within these microenvironments, to shed new light on the physiological origins of excitable flagellar dynamics.