Evolution and caste plasticity of brain architecture in Neotropical army ants (Formicidae: Ecitoninae)

We used histology and neuroanatomical techniques to measure the volumes of brain regions in Neotropical army ant species. We sampled one to three species from each of the five known genera of Ecitoninae. Species ranged widely in body size distributions and in degree of above- versus below-ground activity. Brain size was weakly related to body size. Functionally distinct brain regions, particularly the mushroom body calyces and the optic lobes, were relatively large in the genus Eciton, likely related to the evolution of above-ground activity in this genus. This pattern gives evidence for potential re-expansion of brain regions following reduction in ancestral taxa. Eciton soldiers showed some evidence of reduced brain investment relative to body size, suggesting there is caste-related brain plasticity.