Back to the roots: the importance of using simple insect societies to understand the molecular basis of complex social life.

The evolutionary trajectories toward insect eusociality come in two broad forms. In species like wasps, bees, and ants, the first helpers remained at the nest primarily to help with brood care. In species like aphids and termites, on the other hand, nest defense was initially the primary ecological driving force. To better understand the molecular basis of these two alternative evolutionary trajectories, it is therefore important to study the mechanistic basis of brood care and nest defense behavior. So far, most studies have compared morphologically distinct castes in advanced eusocial species of ants, bees, wasps, and termites. However, the interpretation of such comparisons is limited by multiple confounding factors and the fact that castes are typically fixed and cannot be manipulated at the adult stage. In this review, we argue that conducting molecular studies of brood care and nest defense in simpler, more flexible insect societies may complement studies of advanced eusocial insects and provide avenues toward more functional analyses. We review the available literature and propose candidate study systems for future molecular investigations of brood care and nest defense in social insects.