Keeping an Eye on Plasticity Genes: Insulin/TOR Pathway Components Mediating Nutritional Plasticity of Eyes Within and Between Sex

The eyes of insects exhibit extreme morphological variation through changes in size and shape. While the model organism Drosophila melanogaster has been used to elucidate the underlying gene networks and cell-signalling pathways that regulate the patterning and growth of the eye, insight into the regulators of nutrient-dependent sizing and allometry within and between the sexes remains poorly understood. Using a screen approach of the well characterized and ancient Insulin/TOR pathway, we show that perturbations of different nodes of this pathway modulate the impact of nutritional variation on the sizing and scaling of the eye to varying degrees, and that this is further influenced by sex. When starved, wild-type flies decrease in eye size and body size proportionately in females, yet males change eye-to-body size disproportionately. Subsequently we used previously validated RNAi lines to knockdown each component of the Insulin/TOR pathway in an eye-specific manner to characterize their individual influence in modulating nutritional plasticity of eye sizing. Surprisingly, this resulted in a range of size and scaling variation, components modulating the plastic response on eye size mean, eye-to-body slope, intercept, as well as eye size variance, some effects ranging in magnitude from shutting off plasticity to amplifying, and some which were sex-limited. More generally, the morphospace of a trait can evolve within and across the sexes through modifications of plasticity genes.