By D. S. Saunders (Auth.)
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Development. This procedure showed that the rhythm could not be initiated until after the midpoint of embryogenesis (132 hours from deposition) (Fig. 6). Similar data for systematic transfers from LD 12: 12 to DD, or systematic exposures to 15 minutes of light, were also obtained. These results suggested that either the oscillator controlling egg hatching was not "differentiated" until 132 hours, or that it was present from the outset but was not coupled to the light cycle. The second of these alternatives was considered possible because a pinkish pigment appeared in the egg at about the time when initiation could first be achieved.
The pupal eclosion rhythm of D. pseudoobscura and D. melanogaster can be initiated by a light pulse or by the transfer of the population from LL to DD at any stage of larval or intra-puparial development (Bünning, 1935; Pittendrigh, 1954; Brett, 1955; Zimmerman and Ives, 1971). The oscillation governing eclosion is thus observed to operate continuously throughout post-embryonic development and to be unaffected by the extensive morphological reorganization that occurs during metamorphosis. Larval and pupal sensitivity is also the rule for the Mediterranean flour moth Anagasta kühniella (Moriarty, 1959), but in Dacus tryoni (Bateman, 1955) and Sarcophaga argyrostoma (Saunders, 1976, 1978a) entrainment and phase control can only be achieved with the larval stages, sensitivity to light coming to an end at puparium-formation.
With PPS 12: 12 simulation is less good in the sense that the phase relationship (ψ) of the rhythm to the pulse acting as dawn is no longer the same as that under a complete photoperiod of 12 hours. With skeletons longer than 14 hours (PPS14 : 10 and over), however, the light fails completely to simulate a 14-hour photoperiod and the oscillator "leaps" to the second "interpretation", namely that of PPS 10 : 14. In D. 7 hours, the rhythm always assumes a phase-relation which is characteristic of the shorter duration (Pittendrigh, 1966).