Endocrine fine-tuning of daily locomotor activity patterns under non-starving conditions in Drosophila

Animals need to balance competitive behaviours to maintain internal homeostasis and to reproduce. The underlying mechanisms are complex, but typically involve neuroendocrine signalling. Using Drosophila, we systematically manipulated signalling between energy-mobilising endocrine cells producing adipokinetic hormone (AKH), octopaminergic neurons and the energy-storing fat body to assess whether this neuroendocrine axis involved in starvation-induced hyperactivity also balances activity levels under ad libitum access to food. Our results suggest that AKH signals via two divergent pathways that are mutually competitive in terms of activity and rest. AKH increases activity via the octopaminergic system during the day, while it prevents high activity levels during the night by signalling to the fat body. This regulation involves feedback signalling from octopaminergic neurons to AKH-producing cells. AKH-producing cells are known to integrate a multitude of metabolic and endocrine signals. Our results add a new facet to the versatile regulatory functions of AKH-producing cells by showing that their output contributes to shape the daily activity pattern under ad libitum access to food.