The Role of Light in the Initiation of Circadian Activity Rhythms of AdultDrosophila Melanogaster

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Abstract
Rearing Drosophila melanogaster in constant darkness (DD) for multiple generations disrupts the circadian activity rhythm of adults. In order to determine under what conditions normal rhythms can be initiated, DD-reared Drosophila (either the wild type or the periodshort [pers] mutant) were exposed to light either as embryos, third-instar larvae, or adults. Exposing DD-reared flies to light as embryos or larvae had no effect, while exposing them as adults fully restored normal rhythms in pers and partially restored normal rhythms in the wild type. The percentage of adults with normal rhythms was not significantly different between animals given a 1-h pulse of light as adults and animals given two LD cycles as adults. LD-reared and DD-reared animals given 2 LD cycles were synchronous. In the latter, offset of activity followed the LD transition (CT 12) by 2-6 subjective hours in pers and 2-3 subjective hours in per+. Circadian rhythms did not exhibit phase coherence in the other treatments.