The distinct roles of insulin signaling in polyphenic development

Many insects have the ability to develop alternative morphologies in response to specific environmental signals such as photoperiod, temperature, nutrition and crowding. These signals are integrated by the brain and result in alternative patterns of secretion of developmental hormones like ecdysone, juvenile hormone and insulin-like growth factors, which, in turn, direct alternative developmental trajectories. Insulin signaling appears to be particularly important when the polyphenism involves differences in the sizes of the body, appendages and other structures, such as wings, mandibles and horns. Here we review recent advances in understanding the role of insulin signaling, and its interaction with other hormones, in the development of polyphenisms.