Extent of mismatch between the period of circadian clocks and light/dark cycles determines time‐to‐emergence in fruit flies

Circadian clocks time developmental stages of fruit flies Drosophila melanogaster, while light/dark (LD) cycles delimit emergence of adults, conceding only during the “allowed gate.” Previous studies have revealed that time‐to‐emergence can be altered by mutations in the core clock gene period (per), or by altering the length of LD cycles. Since this evidence came from studies on genetically manipulated flies, or on flies maintained under LD cycles with limited range of periods, inferences that can be drawn are limited. Moreover, the extent of shortening or lengthening of time‐to‐emergence remains yet unknown. In order to pursue this further, we assayed time‐to‐emergence of D. melanogaster under 12 different LD cycles as well as in constant light (LL) and constant dark conditions (DD). Time‐to‐emergence in flies occurred earlier under LL than in LD cycles and DD. Among the LD cycles, time‐to‐emergence occurred earlier under T4–T8, followed by T36–T48, and then T12–T32, suggesting that egg‐to‐emergence duration in flies becomes shorter when the length of LD cycles deviates from 24 h, bearing a strong positive and a marginally negative correlation with day length, for values shorter and longer than 24 h, respectively. These results suggest that the extent of mismatch between the period of circadian clocks and environmental cycles determines the time‐to‐emergence in Drosophila.