Behavior of period-altered circadian rhythm mutants ofDrosophila in light: Dark cycles (Diptera: Drosophilidae)

Adults of Drosophila melanogasterhad their locomotor activity monitored under conditions of cycling light and dark (12 h each per cycle). The elementary behavior of wild-type flies under these “LD” conditions fluctuated between levels of high and levels of low activity. Two high-activity peaks occurred within a given cycle: one at about dawn; the other, at around dusk. Such accentuated activity levels gradually subsided to troughs in the middle of the day and of the night, after which the flies anticipated the next environmental transition by gradually becoming more active. Descriptions of these activity profiles were augmented by newly developed formal analyses of the “diel rhythm” phases (based in part on digital filterings of the raw behavioral data). The applications of these analyses led to objective, automated determination of when in the morning and the evening the flies' activity peaks occur. This normal diel behavior was compared to the locomotor activity and phase determinations for a series of rhythm variants. Most of these involved mutations at the period (per)locus and germ-line transformants bearing normal or altered forms of DNA cloned from this “clock gene.” Such genetic variants have been shown previously to exhibit, in constant darkness, strain-specific circadian periods ranging from about 19 to about 29 h. We now show that the phases of the evening peaks of activity under LD conditions were correspondingly earlier than normal for the short-period mutants and later than normal for those with long circadian cycle durations. The morning peaks, however, moved (in comparison to the normal phase position) minimally under the influence of a given pervariant.