Endocrine Influences on Insect Societies

Insect societies are defined by an intricate division of labor among individuals. There is a reproductive division of labor between queens and workers, and a division of labor among workers for all activities related to colony growth and development. The different castes in an insect society and the diverse roles they play are extreme manifestations of phenotypic plasticity. This chapter reviews the roles that various hormones play in governing different forms of division of labor in the insect societies, including juvenile hormone (JH), the ecdysteroids, insulin, biogenic amines, and neuropeptides. We discuss how these endocrine systems regulate diverse physiological and molecular processes during development and adulthood by serving as key signal transducers to combine information about internal and external state. We also draw on the results of a burgeoning literature on transcriptomic studies to propose a theoretical framework for how hormones modulate brain transcriptomic architecture underlying social behavior to generate phenotypic plasticity. A key feature of this framework is the notion that there has been neofunctionalization of certain endocrine systems via the rewiring of ancestral transcriptional regulatory networks. We end this chapter by presenting a mechanistic model for the evolution of insect sociality based on the co-option of endocrine pathways to respond to and regulate social behavior, using JH as a model system. In particular, we explore the relationship between the degree of neofunctionalization in JH-related pathways, the life stage at which JH modulates social stimuli, and the degree of phenotypic plasticity exhibited by various species.