Division of labor in workers of the leafcutter ant Atta sexdens (Hymenoptera: Formicidae) is correlated with brain structure

Brain size in ant workers may vary according to behavioral demands of performing tasks. In Atta sexdens, worker polymorphism is linked to division of labor based on body size. This study quantified the volumes of the antennal lobe, optic lobe, and mushroom body calyx across workers with different body size. We hypothesize that task specialization in A. sexdens is associated with variation in the volumes of brain compartments, primarily those related to visual and olfactory processing and information integration, such as the optical and antennal lobes and mushroom body, similarly to what is observed in closely related species. Soldiers possess spherical glomeruli in the antennal lobes, including two macroglomeruli. The soldiers have larger head capsules and whole brain volume than the other subcastes but the foragers with larger head than gardeners and waste removers have similar brain size, likely reflecting the task diversity. The optic and antennal lobes volumes were similar among the subcastes, whereas the mushroom body calyx was larger in soldiers. The relative sizes of the three brain compartments evaluated were similar among the subcastes. Synapse density was similar across subcastes. Despite the differences in the brain and calyx volume in soldiers, the similar sizes among foragers, gardeners, and waste removers, which has different head capsule sizes support the hypothesis that brain structure reflects behavioral specialization in A. sexdens.