A comparative approach to cooperative transport in ants: individual persistence correlates with group coordination

Abstract

When groups of ants work together to carry large objects—called cooperative transport—they must form consensus on a travel direction. In many species, groups are unsuccessful at this decision, and deadlock. In other collective decisions, including nest-site selection in honeybees, individuals’ enthusiasm or recruitment intensity for a given option affects the selection process. A similar mechanism may be important during cooperative transport in ants and may account for coordination differences among species. Results from theoretical models suggest that individuals’ persistence—their reluctance to give up or change their preferred direction—may promote coordination. More persistent individuals formed more successful groups in a theoretical context. As an empirical test of this hypothesis, I examined cooperative transport in four ant species that differ substantially in their group-level coordination, from exceedingly coordinated to rarely successful. I focused on the beginning of transport, evaluating groups’ transitions from uncoordinated to successful. I measured two types of persistence at the individual level—total engagement effort and local engagement time—and I measured group coordination for each species. In one species, I also manipulated persistence by adding a force equivalent to infinitely persistent ants to the existing transport groups. Species with more persistent individuals succeeded more often and formed more coordinated transport groups, with more direct paths. Furthermore, adding two infinitely persistent ants to the existing groups seemed to moderately increase their path directness. These results support the hypothesis that high individual persistence promotes group coordination during cooperative transport, and this study informs the mechanisms of emergent coordination.