Group size and decision making: experimental evidence for minority games in fish behaviour

• Published in: Animal behaviour Vol. 155; pp. 9 - 19
• Main Authors: Swain, Anshuman, Fagan, William F.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2019
• Subjects: animals; decision making; fish behavior; fish behaviour; fish communities; group size; guppies; inductive learning; memory; minority games; Poecilia reticulata; inductive learning; fish behaviour; minority games; guppies; decision making
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/j.anbehav.2019.05.017

Animals tend to learn and make decisions inductively, and simple, individual-level behavioural decisions can scale up to yield interesting emergent properties at the population level. The minority game is a theoretical formulation based on the principle of inductive learning, wherein a group of individuals, each facing two equivalent choices, self-organize to achieve maximum coordination. Coordination increases with memory length up to a certain threshold, and thereafter, at very high memory lengths, decisions resemble a random choice game. We invoked and observed minority games in guppies, Poecilia reticulata, by forcing them to choose between two symmetric chambers in a series of repeated trials. At an intermediate timescale, guppies self-organized into a globally efficient state featuring maximum coordination. After a large number of trials, the guppies approached a steady state in which they behaved as if they were randomly choosing between the two chambers. Intriguingly, both the time taken to reach this globally efficient state (i.e. learning time) and the grouping behaviour for decision making depended on the sexual composition of the fish populations. We identified a positive correlation between group size and learning time in the experiments, which we further explored using simulations to uncover the form of decision-making framework at play, testing between a leader-based framework and a consensus-based one. Our simulations supported the presence of a consensus-based decision-making process in the system. This work also provides an unexplored general framework to further investigate and understand simple decision-making dynamics and structure in animal groups. •We examined learning and group behaviour in guppies via minority game formulation.•Group size and learning time were positively correlated and sex dependent.•Females formed larger groups and took longer to learn than males.•Consensus-based decisions may explain observed group size–‘learning’ trends.