Data from: Polymorphism and division of labour in a socially complex ant: neuromodulation of aggression in the Australian weaver ant, Oecophylla smaragdina

Complex social structure in eusocial insects can involve worker morphological differentiation accompanied by behavioral specialization. Neuroanatomical variation may underscore worker division of labor, but the regulatory mechanisms of size-based task specialization in polymorphic species are unknown. The Australian weaver ant, Oecophylla smaragdina, is an ecologically dominant and socially complex species exhibiting a striking worker polyphenism: larger major workers aggressively defend arboreal territories, whereas smaller minors specialize on nursing within nests. Here we demonstrate that the neuromodulator octopamine regulates worker size-related aggression in O. smaragdina. By quantifying the monoamine content of individual brains, we found that majors had significantly higher titers of octopamine than minors. Furthermore, octopamine was positively and specifically correlated with the frequency of aggressive responses to non-nestmates, a key component of territorial defense. Pharmacological manipulations that effectively switched octopamine action in major and minor worker brains reversed levels of aggression characteristic of each worker size class. Results suggest that altering octopamine action is sufficient to produce differences in aggression characteristic of size-related social roles in this species. Neuromodulators therefore may generate variation in responsiveness to task-related stimuli associated with worker size differentiation and collateral behavioral specializations, a significant component of division of labor in complex social systems.