Game played by tandem-running ants: Hint of procedural rationality.

Navigation during colony relocation by the tandem-running ants, Diacamma indicum, is a tour de force of biological traffic coordination, as this directly impact the survival and fitness of the whole colony. Even on one-lane paths, the ants tactfully manage a bidirectional flow: An informed individual (termed leader) guides one nest mate (termed follower) to a new optimal nest, and then returns to recruit additional followers (one follower at a time). We propose that encounters between the ants moving in opposite directions can be modeled within the framework of game theory, leading to an understanding of the mechanism behind observed behaviors. Our experiments reveal that, upon encountering a tandem pair (a leader and its follower) on a narrow path, the returning leader reverses her direction and proceeds toward the new nest again. This observed behavior is consistent with game-theoretic predictions, provided the assumption of perfect rationality is relaxed in favor of bounded rationality-specifically, procedural rationality, i.e., an agent explores all her actions independently before adopting a particular action. In other words, the experimental outcomes are consistent with sampling equilibrium-the game theoretic equilibrium realized when procedural rational players are pitted against one another-but not with Nash equilibrium. Our work, which strives to bring the essence of behavioral game theory into the world of ants, demonstrates sampling equilibrium in a scenario without human players, extending the concept beyond its traditional application to human decision-making.