Fitness consequences of cooperative colony founding in the desert leaf-cutter ant Acromyrmex versicolor

The evolution of cooperative colony foundation (pleometrosis) in ants has been attributed to conversion of extra resources into increased competitive ability. Most cooperative founding species provide these additional resources from internal fat stores; however, in those species that forage for resources, the extent and type of individual investment in multiqueen colonies is not well understood. We compared singly- and group-founded laboratory colonies of the desert leaf-cutter ant Acromyrmex versicolor to investigate how cooperation affects colony survival, foraging success, and worker production. Under laboratory conditions, single foundresses were significantly less likely to initiate a successful symbiotic fungus garden, which inevitably led to colony starvation and death. If gardens were initiated successfully, however, there was no difference in the growth trajectories and foraging patterns between colony types. Cooperation in this species may more likely be maintained by survival benefits than by growth rate differences, which may be constrained in groups by individual and colony-level costs.