| Summary: | <p>Abstract</p> <p>Background</p> <p>Circadian clocks have been implicated in the regulation of pre-adult development of fruit flies <it>Drosophila melanogaster</it>. It is believed that faster clocks speed up development and slower clocks slow it down. We established three sets of <it>D. melanogaster </it>populations (<it>early</it>, <it>control </it>and <it>late</it>). The <it>early </it>and <it>late </it>populations were raised by selecting for flies that emerged either in the morning or in the evening under 12:12 hr light/dark (LD) cycles. After 75 generations of selection, the time course and waveform of the adult emergence and activity rhythms of the <it>early </it>and the <it>late </it>populations diverged from each other as well as from the <it>controls</it>. In this paper, we report the consequence of this selection on the rate of pre-adult development.</p> <p>Results</p> <p>We assayed the pre-adult development time of the selected and control populations under 12:12 hr LD cycles and constant darkness (DD). Under LD cycles, the <it>early </it>populations develop faster than the <it>controls</it>, while the <it>late </it>populations develop slower than the <it>controls</it>. Although flies take longer to develop under DD than in LD, the relative differences between the mean development times of the selected and control populations remain unaltered in DD. In a separate experiment designed to investigate the effect of time of egg collection and experimental conditions on the duration of pre-adult stage, we assayed the development time of the selected and control populations by collecting eggs at different times of the day (morning and evening) and by assaying their pre-adult development time under constant light (LL), LD, and DD conditions. Irrespective of the time of egg collection and assay light regime, the <it>late </it>flies continue to develop slower than the <it>early </it>flies.</p> <p>Conclusion</p> <p>The results of our study clearly indicate that selection on the timing of adult emergence alters the rate of pre-adult development in <it>D. melanogaster</it>. The timing of egg collection as well as assay light regime does not have any measurable effect on the relative differences between the developmental rates of the <it>early </it>and the <it>late </it>flies. Taken together these results appear to suggest that pleiotropic effects of clock genes mediate correlated changes in the timing of adult emergence and the rate of pre-adult development in <it>D. melanogaster</it>.</p>
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