The central role of clock genes in orchestrating diverse timing behaviors in Drosophila: An integrative genetic and molecular review

Biological timing spans multiple scales, from second-to-minute behavioral decisions to daily rhythms and seasonally adjusted physiological states. Here, we use Drosophila clock genes as a model of gene co-option and functional modularity, asking how conserved circadian components are redeployed across diverse behavioral and physiological timescales. This review synthesizes current evidence on how core clock genes, including period (per), timeless (tim), Clock (Clk), and cycle (cyc), contribute not only to circadian rhythmicity but also to sleep regulation, developmental and reproductive timing, feeding and metabolic homeostasis, seasonal dormancy-related responses, and interval timing-like mating duration behaviors. Across these domains, clock-gene functions are shaped by cellular context, circuit architecture, transcriptional feedback, post-transcriptional and post-translational regulation, and environmental inputs such as light, temperature, nutrition, and social experience. Rather than treating these timing phenomena as isolated processes, we argue that they can be understood as examples of modular reuse of conserved molecular components. By centering the review on Drosophila and referring to mammalian studies only as comparative context where relevant, we highlight how clock-gene systems can be adapted to regulate behavior across biological timescales.