Prothoracicotropic hormone modulates environmental adaptive plasticity through the control of developmental timing

Adult size and fitness are controlled by a combination of genetics and environmental cues. In Drosophila, growth is confined to the larval phase and final body size is impacted by the duration of this phase, which is under neuroendocrine control. The neuropeptide prothoracicotropic hormone (PTTH) has been proposed to play a central role in controlling the length of the larval phase through regulation of ecdysone production, a steroid hormone that initiates larval molting and metamorphosis. Here, we test this issue by examining the consequences of null mutations in the ptth gene on Drosophila development. Loss of ptth causes several developmental defects including a delay in developmental timing, increase in critical weight, loss of coordination between body and imaginal disc growth, and reduced adult survival in sub-optimal environmental conditions like nutrition deprivation or high population density. We show that these defects are caused by a decrease in ecdysone production associated with altered transcription of ecdysone biosynthetic genes. Therefore, the PTTH signal contributes to proper coordination between various environmental cues and the developmental program to ensure individual fitness and survival.