A game played by tandem-running ants: Hint of procedural rationality

Navigation through narrow passages during colony relocation by the tandem-running ants, $\textit{Diacamma}$ $\textit{indicum}$, is a tour de force of biological traffic coordination. Even on one-lane paths, the ants tactfully manage a bidirectional flow: Informed individuals (termed leaders) guide nest-mates (termed followers) from a suboptimal nest to a new optimal nest, and then return to recruit additional followers. We propose that encounters between the ants moving in opposite directions can be modelled within the framework of game theory leading to an understanding of the mechanism behind observed behaviours. 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 as if she becomes the leader guiding a follower. This observed behaviour is consistent with game-theoretic predictions, provided the assumption of perfect rationality is relaxed in favour of bounded rationality -- specifically, procedural rationality. In other words, the experimental outcomes are consistent with sampling equilibrium but not with Nash equilibrium. Our work, which strives to induct the essence of behavioural game theory into the world of ants, is first ever report of realizing sampling equilibrium in scenarios not involving human players.