Social interactions drive the evolution of emergent collective behavior among ant species.

Most animal collective behaviors are emergent phenotypes that arise from interactions between multiple individuals. Little is known about the factors that lead to the evolution of differences in emergent phenotypes across species. Acorn ants (genera Temnothorax and Leptothorax) are a useful model clade to quantitatively study how emergent collective behavior evolves because acorn ants possess a collective behavior that differs significantly between species; the ants inside each colony synchronize their rest/activity rhythms with each other, but the rhythmicity and typical cycle period of these collective oscillations varies between species. Using behavioral tracking data from experimentally size-controlled colonies across eight different acorn ant species, we estimated species-specific parameter values for a mathematical model of ant synchronization. We then mapped these parameter values onto a molecular phylogeny to determine what factors are most important for the diversification of the collective-level traits of species’ synchronized activity cycles. Our results suggest that the effects of social interactions among individuals may be more important in driving the diversification of behavioral synchronization than the properties of animals’ intrinsic biological clocks.