Maintaining robust size across environmental conditions through plastic brain growth dynamics

Organ growth is tightly regulated across environmental conditions to generate an appropriate final size. While the size of some organs is free to vary, others need to maintain constant size to function properly. This poses a unique problem: how is robust final size achieved when environmental conditions alter key processes that regulate organ size throughout the body, such as growth rate and growth duration? While we know that brain growth is ‘spared’ from the effects of the environment from humans to fruit flies, we do not understand how this process alters growth dynamics across brain compartments. Here, we explore how this robustness in brain size is achieved by examining differences in growth patterns between the larval body, the brain and a brain compartment—the mushroom bodies—in Drosophila melanogaster across both thermal and nutritional conditions. We identify key differences in patterns of growth between the whole brain and mushroom bodies that are likely to underlie robustness of final organ shape. Further, we show that these differences produce distinct brain shapes across environments.