Abstract
Cooperative transport of large food loads by Paratrechina longicornis ants demands repeated decision-making. Inspired by the Evidence Accumulation (EA) model classically used to describe decision-making in the brain, we conducted a binary choice experiment where carrying ants rely on social information to choose between two paths. We found that the carried load performs a biased random walk that continuously alternates between the two options. We show that this motion constitutes a physical realization of the abstract EA model and exhibits an emergent version of the psychophysical Weber’s law. In contrast to the EA model, we found that the load’s random step size is not fixed but, rather, varies with both evidence and circumstances. Using theoretical modeling we show that variable step size expands the scope of the EA model from isolated to sequential decisions. We hypothesize that this phenomenon may also be relevant in neuronal circuits that perform sequential decisions.
Highlights
The capacity to decide between multiple options is key to the survival of any organism
We further show how this correction emerges from an established microscopic model of the decisions taken by individual ants while engaged in cooperative transport [33] and hypothesize that similar corrections may be apparent in neuronal circuits involved in sequential decision making
Experiments were initiated after a short recruitment stage in which we made sure that ants reach the load through all available exits
Summary
The capacity to decide between multiple options is key to the survival of any organism. There are many analogies between the decision-making mechanisms in animal groups and in the neuronal ensembles within the relevant decision-making areas in a single brain [24,25,26,27] Among these analogies, the EA model has been shown to apply to consensus single-shot decisions taken by ants [28]. We confronted the ants with a binary choice within an environment that constitutes a physical realization of the abstract EA model This was achieved by placing the load within a one-dimensional track with two decoy exits, one at each end. We further show how this correction emerges from an established microscopic model of the decisions taken by individual ants while engaged in cooperative transport [33] and hypothesize that similar corrections may be apparent in neuronal circuits involved in sequential decision making. We show how the ants’ behavior can occupy different regimes of decisionmaking space and theoretically argue that these correspond to differences in risk management
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