ON THE ABSENCE OF CIRCADIAN RHYTHMICITY IN DROSOPHILA PSEUDOOBSCURA PUPAE

¹ Department of Biology, Amherst College, Amherst, Massachusetts, 01002

1. Although circadian rhythms are systematically and physiologically ubiquitous in eucaryotic organisms, they are not evident under certain experimental conditions. For example, there is no circadian rhythm in adult emergence in populations of Drosophila pseudoobscura if the organism is raised in constant dark and temperature.

2. In general, such overt arhythmicity could be interpreted as due to asynchrony or true arhythmicity of constituent parts (organelles in cells; cells and organs in individuals; individuals in populations).

3. In the case of the circadian rhythm of adult emergence in Drosophila pseudoobscura, a distinction between these two interpretations of arhythmicity is made possible by comparing the rhythm-phase shifting and rhythm-inducing effect of the same temperature signal. It was concluded that arhythmicity of Drosophila populations was due to a true arhythmicity of constituent parts (individual flies).

4. Other experiments are mentioned in which the arhythmicity of populations and individuals is attributable to a true arhythmicity of constituent parts.

5. This finding presents difficulties for hypotheses asserting the importance of circadian rhythmicities in the physiology of eucaryotic organisms.

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