Dresden 2017 – scientific programme

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BP: Fachverband Biologische Physik

BP 12: Microswimmers I (Joint Session DY/BP)

BP 12.3: Talk

Tuesday, March 21, 2017, 10:15–10:30, HÜL 186

Optimal decision making in sperm chemotaxis — •Justus A. Kromer and Benjamin M. Friedrich — cfaed, TU Dresden

Sperm cells follow dilute chemical gradients to find the egg in a process termed chemotaxis. To evaluate local concentrations of chemoattractant, sperm detect single attractant molecules, while moving along helical paths. This noisy chemical input signal regulates the flagellar beat to steer the cell up-gradient. Recent experiments showed that sperm cells can switch between two distinct steering modes in a situation-specific manner [1]. While swimming up-gradient, cells employ a mode of conservative steering, characterized by slow bending of the helical swimming path towards the direction of the concentration gradient. In contrast, if a cell accidentally swims down-gradient, it responds with a vigorous steering maneuver, characterized by fast helix bending.

Here, we present a theoretical description of this cellular decision making, formulated as a Markov decision process in the framework of a stochastic single-player game. We predict that decision making would provide no benefit in a hypothetical noise-free world, but substantially increases the chances to find the egg at physiological levels of sensing noise. Our work exemplifies the fundamental trade-off choice between responding accurately or responding fast for navigating cells.

[1] JF. Jikeli et al. Nature Communications 6, 7985 (2015)