Organisms use mode-switching to solve the explore-vs-exploit problem

Abstract

Movement and sensing are linked in organisms as their sensors are embedded in their bodies. This inescapable link results in a behavioral conflict between producing costly movements for gathering information ("explore") [1-3] versus using previously acquired information to achieve a goal ("exploit") [4]. Optimally trading-off exploration and exploitation is an intractable problem [6-8], and the strategies that animals utilize to resolve this conflict are poorly understood [5]. Here we show that weakly electric fish (\textit{Eigenmannia virescens}) [2, 3, 9] use a mode-switching strategy that solves the explore-exploit conflict [5] during a refuge tracking task [10-13] and show that this strategy is modulated by sensory salience. Fish produced distinctive non-Gaussian (i.e., non-normal) distributions of movement velocities characterized by sharp peaks for slower, task-oriented "exploit" movements and broad shoulders for faster, "explore" movements. Surprisingly, measures of non-normality increased (rather than decreased) in relation to increased sensory salience. Reanalysis of published data revealed that this distinctive distribution of movement velocities is produced by phylogenetically diverse organisms, from amoeba to humans. Further, other species exhibited the same counter-intuitive modulation of mode-switching in relation to sensory salience. We propose a parsimonious, state-uncertainty based mode-switching heuristic that reproduces the distinctive velocity distribution and explains its relationship to sensory salience. This mode-switching strategy likely manifests in diverse biological mechanisms, from cellular processes for single-cell motility to network-level processes for the control of movement in animals.

Noisy circumnutations facilitate self-organized shade avoidance in sunflowers

“…We therefore interpret circumnutations as functional noise. Indeed, in motile animal systems such wide distributions of movement velocities are frequently identified with enhancement of behavioral processes, for example truncated power laws yielding Lévy flights, associated with animal search and foraging [44], and broad shouldered distributions related to sensory salience [17, 16]. We note that while we find here that circumnutations are beneficial, they also pose a cost to the plant, both due to the continuous change in leaf orientation (which by definition will not always be in the direction of light), as well as the mechanical cost of drooping sideways compared to growing straight.…”

“…In biological systems, noise is often identified as being functional , exhibiting a wide spectrum of manifestations. For example, organisms use noise in order to increase sensory salience, ultimately enabling them to balance the behavioral conflict between producing costly movements for gathering information (“explore”) versus using previously acquired information to achieve a goal (“exploit”) [15, 16, 17]. Additionally, the navigation paths of bacteria [18], insects [19], and mammals [20, 21] exemplify the intricate trajectories adopted to counterbalance uncertain surroundings [22].…”