Parameter tuning facilitates the evolution of diverse tunneling patterns in termites
The nest structures built by social insects are complex group-level patterns that emerge from interactions among individuals following simple behavioral rules. The theory of complex systems predicts that there is no simple one-to-one relationship between variations in collective patterns and variation in individual behaviors; therefore, it is essential to know how actual behavior evolves to change pattern formation. Here we demonstrate that the evolutionary divergence of termite tunneling patterns is achieved by quantitative tuning of shared behavioral rules, rather than the acquisition of novel behaviors. We compared tunnel formation between two closely related species, Reticulitermes tibialis and Heterotermes aureus, and found that H. aureus builds more highly branched tunnels than R. tibialis. Our behavioral analysis and data-based modeling revealed that these species share the same behavioral repertoire, but a quantitative difference in the probability of sidewall excavation leads to diverse tunneling patterns. In contrast, we also found that Paraneotermes simplicicornis, which evolved tunneling independently, possesses a distinct behavioral repertoire, but shows convergence of branching patterns with R. tibialis. These results elucidate the complex relationship between individual behavior and group-level patterns; in some cases, distinct behavioral rules can produce similar group-level patterns, but in others, a common rule set can yield distinct patterns via parameter tuning. The evolutionary process of collective behavior is flexible and much more complex than we can infer from group-level patterns alone.