Age, size, brain and subcaste evolution in the ant genus Pheidole

To understand subcaste evolution and division of labor in the ant genus Pheidole, we examined major worker morphological specialization and task flexibility in a diverse Amazonian community, and determined the neural underpinnings of age- and subcaste-related behavior in ecologically different North American species. In tropical Pheidole, brood nursed by majors had lower survival but similar growth rates to brood tended by minors; there was no significant association between degree of major worker morphometric specialization and nursing efficacy. Subcastes and age classes of focal species differed significantly in brain anatomy and chemistry, and age-related task performance was causally linked to amine levels.