Figure 1

Rhythms of Drosophila melanogaster. The fruitfly generates behavioral, molecular, and physiological rhythms on several different time scales. Examples (a) through (d) depict circadian rhythms, while (e) and (f) involve ultradian (high-frequency) cycles. The eclosion rhythm, plotted in (a) as numbers of emerging flies over time, is a population rhythm associated with metamorphosis from the pupal to the adult stage. In constant darkness (DD) emergence of adults from the pupal stage typically occurs in the early part of the subjective day, corresponding to literal daytime in light-dark (LD) cycles (alternating white and shaded blocks, left side of plot). (b) Adult behavioral rhythms are usually assayed by monitoring daily locomotor activity. The behavioral record shown is that of an adult wild-type male. The temporal distribution of activity was measured by the number of times he tripped an optical switch with the counts typically collected every half hour for several days. The photic conditions are depicted as in (a). (c) Activity of a firefly luciferase transgene driven by the timeless promoter. A transgenic male ingested luciferin substrate; and a rhythmic signal of bioluminescense was registered each hour, leading in this case to plotting of bioluminescent counts over a six-day timespan. (d) An isolated wing pair, dissected from the same type of transgenic fly as in (c), also displayed rhythmicity when bathed in a luciferin-containing medium. In this example the data are normalized as described in the text. (e) A one-second bout of male courtship song, the beginning of which (between 0 and 0.2 seconds) consisted of "sine" singing (generation of humming sounds by male wing vibrations). The sine-song episode proceeded into a train of tone pulses, which are produced at a rate of ca. 30 per second (by D. melanogaster males) such that the interpulse interval (I PI) is ca. 35 msec. An IPI rhythm is defined by systematic increases then decreases, etc., in the rates of pulse production; the duration of one such cycle is ca. one minute (in songs of this species). The ordinate for this song-bout plot is in arbitrary units, because this record reflects changes in voltage that have more to do with the monitoring equipment than the changes in pressure corresponding to varying sound levels per se. (f) A pupal cardiogram. The rhythmic heartbeat moves blood (hemolymph) throughout the open circulatory system of the animal. The motion of the heart muscle is plotted in arbitary units because the relative changes in voltage reflect changes in illumination (with respect to a non-invasive optical recording technique) produced by the muscle as it moves.