DEVELOPMENTAL STATE AND THE CIRCADIAN CLOCK INTERACT TO INFLUENCE THETIMING OF ECLOSION IN DROSOPHILA-MELANOGASTER

In Drosophila melanogaster, the emergence of adults from their pupal c ases (eclosion) is gated by the circadian clock such that it occurs du ring a window of similar to 8-10 h starting 1-2 h before Lights-on in 12-h Light:12-h dark cycles (LD). This gate is shifted several hours e arlier by the clock mutant per(s), indicating that the clock controls the phase of eclosion under these conditions. Both the day and the tim e of eclosion are determined by the interplay between developmental st ate and the circadian clock. At a certain phase of the circadian cycle , the circadian clock, either directly or through some circadian clock -controlled mechanism, measures developmental state, and those pharate adults that have reached a certain developmental state by this phase eclose during the first available gate, while those that have not wait until a subsequent gate. Using wing pigmentation as a late developmen tal state marker, an early boundary for when the circadian clock asses ses developmental state occurs roughly at the time when lights go out during LD cycles. This event is shifted several hours earlier in per(s ), showing that it is under circadian control. A fly's developmental s tate at the time of developmental assessment also influences when eclo sion will occur (during the gate) in that flies whose wings have becom e pigmented early (12-24 h before assessment) will eclose earlier in t he gate than those whose wings become pigmented late (0-12 h before as sessment). These data suggest that the circadian clock (or some clock- controlled mechanism) measures developmental state (wing pigmentation) in wild-type flies between lights-off and expression of the first clo ck-regulated marker similar to 4-5 h before eclosion and that the deve lopmental state of the fly determines both which gate is chosen for ec losion and when eclosion occurs during that gate.