Moving around without a brain: Evolution of basal cognition in single-celled organisms

ongoing

Even unicellular organisms have a sense of self -- that basal recognition of where their own membranous boundaries end, and where the extracellular environment in which they inhabit begins. Yet unlike the cells in your body, these primitive lifeforms can reproduce, and exist autonomously, most importantly, they can respond to stimuli, and change their behaviour accordingly. Responsive self-movement is a defining characteristic of life, which for simple organisms is essential to enable to them to explore and react to their surroundings, improve their circumstances, and outcompete other cells. In this proposal, I will determine the sensorimotor pathways of unicellular organisms and the physical mechanisms of early movement control, showing that a nervous system is not required for complex behaviour, particularly, 1) motility originating from cell shape changes by cilia and flagella, and 2) the as-yet unexplained surface gliding movement of diatoms which occurs in the complete absence of shape changes. I will develop novel interdisciplinary approaches, merging physiological experiments on diverse unicellular species with unique behavioural features, with theoretical modelling, mathematical/computational analysis of behaviour, as well as robotics-aided hypothesis testing. To highlight the importance of fast, nonequilibrium sensing in unicells and its significance for the evolution of nervous signalling, I will pioneer the integration of high-speed imaging and live-cell perturbations to resolve and understand previously unseen cellular processes and excitable phenomena. These investigations will culminate in novel designs for long-time behavioural assays which will probe the limits of aneural organisms and their capacity to perceive and interact with their surroundings.