Seasonal cycles of reproduction and development are very common in a wide variety of animals that utlize the length of the day as a cue to asses the time of year. The research proposed is directed toward understanding the mechanism by which daylength (or photoperiod) is measured. Previous studies have led to the hypothesis regulates the biological clock that regulates daily (i.e., circadian) rhythms of behavior and metabolism is involved in photoperiodic time measurement. We plan to directly test that hypothesis utilizing and insect, the cricket, Gryllus firmus, as a model system. There are two specific goals of the research program. The first is to confirm that the "circadian clock" is in fact a component of the "photoperiodic clock" that regulates seasonal rhythms. The second is to initiate studies to determine the precise role of the circadian clock in carrying otu the measurement of daylength. Gryllus Firmus females lay eggs that either develop immediately or enter a state of developmental arrest. If the adult female is maintained in long, summer-like days (e.g., 14 h of light per day) then the egge develop, but if the females ismaintained in short, winter-like days the eggs undergo developmentyal arrest for over-wintering. We plan to characterize the anatomical and physiological organization of the circadian system thaty regualtes daily rhythms of locomototr activity, and examine the specific role played by the circadian system in photoperiodic time measurement.
