Animals tend to learn and make decisions inductively, and a number of such simple individual-level behavioral decisions can scale up to yield interesting, population-level emergent properties . A theoretical formulation based on inductive learning and decision-making is called the minority game (MG). In MGs, individuals are each faced with choosing between two equivalent choices, and the game results in a net positive payoff to individuals on the minority side. The system of individuals can self-organize to achieve a maximum coordination, and this coordination increases with individual memory length up to a certain threshold. 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. A total of 191 guppies, reared from a laboratory stock, were sorted into groups of 37-39 fish for five aquaria, in different ratios of male:female individuals. An MG trial consisted of an initial mechanical disturbance in the aquarium center, which led the fish to choose one of the two sides. Subsequently, a cardboard divider was added in the middle of the tank, fish were censused on both sides, and the volume of water on the majority side was reduced by 80% for 30s. Subsequently, the partition was removed, and water added back to the original level. For each of the 5 aquaria, the experimental process consisted of five cycles, with each cycle involving 170 MG trials .
Results/Conclusions
We found that the experimental results matched that of MGs. We could also predict the group size of decision-making using census data and the properties of MGs. At an intermediate number of trials, guppies self-organized into a globally efficient state featuring maximum co-ordination. After many trials, the guppies approached a steady-state where they behaved as if randomly choosing between two sides. This suggests that guppies can sense the nature of stress, use previously available information, and adapt to requisite conditions if the stress is periodically reinforced. Because MG theory is based on an inductive view of learning, these results indicate that guppies learn inductively.
We also found that the number of trials taken by the fish to reach the globally efficient state depended on the size of the groups that they form while making decisions, and group-size in turn has a sex-bias with female guppies grouping more than males under similar conditions.