Correction: Division of labor and brain evolution in insect societies: Neurobiology of extreme specialization in the turtle ant Cephalotes varians.

[This corrects the article DOI: 10.1371/journal.pone.0213618.].

Division of labor and brain evolution in insect societies: Neurobiology of extreme specialization in the turtle ant Cephalotes varians.

Strongly polyphenic social insects provide excellent models to examine the neurobiological basis of division of labor. Turtle ants, Cephalotes varians, have distinct minor worker, soldier, and reproductive (gyne/queen) morphologies associated with their behavioral profiles: small-bodied task-generalist minors lack the phragmotic shield-shaped heads of soldiers, which are specialized to block and guard the nest entrance. Gynes found new colonies and during early stages of colony growth overlap behaviorally with soldiers. Here we describe patterns of brain structure and synaptic organization associated with division of labor in C. varians minor workers, soldiers, and gynes. We quantified brain volumes, determined scaling relationships among brain regions, and quantified the density and size of microglomeruli, synaptic complexes in the mushroom body calyxes important to higher-order processing abilities that may underpin behavioral performance. We found that brain volume was significantly larger in gynes; minor workers and soldiers had similar brain sizes. Consistent with their larger behavioral repertoire, minors had disproportionately larger mushroom bodies than soldiers and gynes. Soldiers and gynes had larger optic lobes, which may be important for flight and navigation in gynes, but serve different functions in soldiers. Microglomeruli were larger and less dense in minor workers; soldiers and gynes did not differ. Correspondence in brain structure despite differences in soldiers and gyne behavior may reflect developmental integration, suggesting that neurobiological metrics not only advance our understanding of brain evolution in social insects, but may also help resolve questions of the origin of novel castes.

Interspecific comparison of mushroom body synaptic complexes of dimorphic workers in the ant genus Pheidole.

Social insects may have morphologically and behaviorally specialized workers that vary in requirements for sensory information processing, making them excellent systems to examine the relationship between brain structure and behavior. The density and size of synaptic complexes (microglomeruli, MG) in the mushroom bodies (MB) have served as proxies for processing ability and synaptic plasticity, and have been shown to vary among insect species that differ in behavioral complexity. To understand the relationship between behavioral specialization and synaptic structure, we examined age-related changes in MG density and size between minor worker and soldier subcastes in two species of Pheidole ants, P. dentata and P. morrisi, that differ in behavior. We hypothesized that task-diverse minor workers would have more densely packed MG than soldiers, and that species-specific differences in soldier repertories would be reflected in MG structure. We also examined MG variation in young and mature minor workers and soldiers, predicting that as workers age and develop behaviorally, MG would decrease in density in both subcastes due to synaptic pruning. Results support the hypothesis that MG density in the lip (olfactory) and collar (visual) regions of the MBs decrease with age in association with increases in bouton size in the lip. However, minors had significantly lower densities of MG in the lip than soldiers, suggesting MG may not show structural variation according to subcaste-related differences in cognitive demands in either species.