Statistics of C. elegans turning behavior reveals optimality under biasing constraints

TL;DR

This study investigates how C. elegans' turning behaviors are shaped by physiological constraints, revealing that their locomotion patterns are optimized for different environmental contexts through a combination of continuous and discrete reorientation strategies.

Contribution

The paper demonstrates that C. elegans' turning behaviors are adapted to constraints, showing optimized orientation fluctuations during exploration and discrete turn selection during escape, highlighting evolved locomotion strategies.

Findings

Orientation fluctuations compensate for turn bias during exploration.

Discrete turn selection enables symmetric escape despite asymmetries.

Turning behaviors are optimized for environmental context.

Abstract

Animal locomotion is often subject to constraints arising from anatomical/physiological asymmetries. We use the nematode C.~elegans as a minimal model system to ask whether such constraints might shape locomotion patterns optimized during evolution. We focus on turning behaviours in two contrasting environmental contexts: (i) random exploration in the absence of strong stimuli and (ii) acute avoidance (escape) navigation upon encountering a strong aversive stimulus. We characterise the full repertoire of reorientation behaviours, including gradual reorientations and various posturally distinct sharp turns. During exploration, our measurements and theoretical modelling indicate that orientation fluctuations on short timescales are, on average, optimized to compensate the constraining gradual turn bias on long timescales. During escape, our data suggests that the reorientation is controlled not by an analog logic of continuous turn-amplitude modulations, but rather through the digital logic of selecting discrete turn types, leading to a symmetric escape performance despite strongly asymmetric turning biases.