Summary
Cultures of Drosophila pseudoobscura pupae raised in 12∶12 hours L/D cycles were subjected to brief light pulses and light steps during early and late subjective night phases.
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1.
A light pulse and a light step during early subjective night evoke dissimilar responses, the pulse effecting a delay phase-shift and the step an advance phaseshift. But a pulse and a step in the latter part of the subjective night evoke a similar response from the system and advance the phase.
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2.
The results are explained by assuming a differential light sensitivity of the underlying system during the subjective night phase itself, with a phase-point of maximum light sensitivity.
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3.
It is postulated that the light “off” fraction of a pulse acts as a new “dusk” in the early subjective night and that the “on” fraction acts as a new-“dawn” in the late subjective night.
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4.
The results of an experiment where a light pulse and a light step combined to form the light treatment bear out the assumptions made above and indicate that the photoinducible phase itself is not phase-locked to environmental time.
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The work reported here was carried out during the tenure of a Research Scholarship of the Alexander von Humboldt-Stiftung. I am grateful to Professor E. Bünning for provision of working facilities in his laboratory, constant encouragement and for suggesting improvements in the manuscript. My thanks are also due to Dr. (Miss) I. Moser for her help in the preparation of the figures.
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Chandrashekaran, M.K. Studies on phase-shifts in endogenous rhythms. Zeitschrift für vergleichende Physiologie 56, 163–170 (1967). https://doi.org/10.1007/BF00340508
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DOI: https://doi.org/10.1007/BF00340508