Limited size-related variation in behavioral performance among workers of the exceptionally polymorphic ant Pheidole rhea

Abstract

Colony fitness is thought to be enhanced through task specialization by physical castes in social insect species that have evolved polymorphic workers. Using the exceptionally polymorphic ant Pheidole rhea as a model, we explored the relationship of worker size and behavior with respect to division of labor by morphologically variable subcastes, hypothesizing that the behavior of minor workers, soldiers, and supersoldiers would align with their social roles. We assayed the ability of different-size workers to detect trail pheromone, generate nest-search locomotion patterns, and recognize non-nestmates and respond with aggressive defense. Our analyses revealed that the largest size class of workers, supersoldiers, can detect trail pheromone at concentrations lower than those eliciting responses from either minors or soldiers. However, there were no size-related differences in locomotion patterns associated with nest-search behavior in a featureless arena, nor was there worker variation in responses to a non-nestmate conspecific. Although the striking polymorphism and allometry of workers suggest role divergence and division of labor in P. rhea, similarity in responses to stimuli associated with extranidal task performance may reflect the conservation of behavioral programs across strongly polymorphic workers.