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First published online February 12, 2007
Journal of Experimental Biology 210, 906-918 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.001354

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Selection on the timing of adult emergence results in altered circadian clocks in fruit flies Drosophila melanogaster

Shailesh Kumar, Dhanya Kumar, Dhanashree A. Paranjpe, Akarsh C. R. and Vijay Kumar Sharma^*

Chronobiology Laboratory, Evolutionary and Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, PO Box 6436, Jakkur, Bangalore 560064, Karnataka, India

View larger version (20K): [in this window] [in a new window]   Fig. 1. Schematic representation of the selection protocol. The selection experiments were carried out under 12:12 h light:dark (LD) cycles [`lights-on' at 08:00 h and `lights-off' at 20:00 h, where Zeitgeber Time 0 (ZT0) denotes lights-on]. Four baseline populations (baseline1..4) maintained for over 75 generations under 12:12 h LD cycles were used to derive four early (early1..4) and four late (late1..4) populations of flies by imposing selection for early and late adult emergence. Four control populations (control1..4) were also raised in a similar manner, except that they did not experience any conscious selection pressure. Flies emerging between 05:00–09:00 h formed the early populations, while those emerging between 17:00–21:00 h made it to the late populations. Flies emerging through out the day were used to raise the control populations. The morning (M) and evening (E) selection windows are shown in the grey boxes in the early and late panels.

View larger version (16K): [in this window] [in a new window]   Fig. 2. Percentage of flies emerging during (A) the morning (M) window (05:00–09:00 h) and (B) the evening (E) window (17:00–21:00 h) in selected and control populations during the 5th, 10th, 25th, 40th and 55th generations. Error bars represent 95% confidence intervals (95%CI) around the mean across four replicate populations (10 vials per populations) for visual hypothesis testing.

View larger version (15K): [in this window] [in a new window]   Fig. 3. The average `difference waveform' of emergence rhythm of the early and late populations [(early–control)/control] and [(late–control)/control] were assayed under a 12:12 h LD cycle at the 5th, 10th, 25th, 40th and 55th generations (Gen.). The `difference waveforms' were estimated by first subtracting the average emergence waveforms of the early and late populations from the controls and then scaling it by the average waveform of the controls. The filled and empty bars denote the dark (20:00–08:00 h) and the light (08:00–20:00 h) phases of the LD cycle and Zeitgeber Time 0 (ZT0) denotes the time at which lights came on.

View larger version (14K): [in this window] [in a new window]   Fig. 4. (A) The phase-relationship between the emergence rhythm and the LD cycle of the selection and control populations at the 5th, 10th, 25th, 40th and 55th generations. The phase-relationship was estimated as the time interval between the primary peak of the emergence and `lights-on' in the LD cycle, averaged over 10 consecutive cycles. Error bars represent 95% confidence intervals (95%CI) around the mean across four replicate populations (10 vials per populations) for visual hypothesis testing. (B) The frequency distribution of phase-relationship of the early, control and late populations under 12:12 h LD cycles. Time (h) is plotted along the x-axis and percentage frequency along the y-axis.

View larger version (9K): [in this window] [in a new window]   Fig. 5. (A) The mean circadian periodicities () of emergence rhythm of the selected and control populations at the 55th generation. Error bars represent 95% confidence intervals (95%CI) around the mean across four replicate populations (10 vials per populations) for visual hypothesis testing. (B) The frequency distribution of the of emergence rhythm of the early, control and late populations. Time (h) is plotted along the x-axis and percentage frequency along the y-axis.

View larger version (5K): [in this window] [in a new window]   Fig. 6. Light pulse-induced phase shift (h) of the emergence rhythm at four phases (CT2, 8, 14 and 20) of the selected and control populations. Circadian Time 0 (CT0) indicates the onset of locomotor activity. Error bars indicate 95% confidence intervals (95%CI) around the mean for visual hypothesis testing. A total of 40 vials were used, of which 10 were used for each replicate population at each phase.

View larger version (42K): [in this window] [in a new window]   Fig. 7. Activity levels of the selected and control flies during the morning (05:00–09:00 h) and evening (17:00–21:00 h) windows of selection. (A) Percentage activity during the morning (M) window in the selected and control populations. (B) Percentage activity during the evening (E) window in the selected and control populations. Error bars represent 95% confidence intervals (95%CI) around the mean for visual hypothesis testing. The average locomotor activity plots of the (C) early (N=161), (D) control (N=171) and (E) late (N=156) flies, monitored under a 12:12 h LD cycle after 55 generations of selection. Locomotor activity profiles are plotted as the mean activity during 1 h bins, averaged over 10 consecutive cycles. The percentage of activity, averaged over 10 successive cycles, is plotted along the ordinate and time of the day (h) along the abscissa. Values are means ± s.e.m., constructed using the variations among the replicate populations within each selection regime. The white and grey vertical bars denote activity levels during the day and night, respectively. Additionally, one representative locomotor activity pattern each of flies from the (F) early, (G) control and (H) late populations are shown. The horizontal black bars denote the dark phase (20:00 h–08:00 h) and white bars represent the light phase of the LD cycle. Zeitgeber time 0 (ZT0) denotes the time at which lights come on under the LD cycle. The average locomotor activity plots of the (I) early (N=32), (J) control (N=27) and (K) late (N=37) flies, during the first cycle of DD following a LD/DD transfer. Horizontal dark grey bars denote the subjective night and light grey bars the subjective day under DD conditions. Vertical dark and light grey bars denote activity during the subjective night and subjective day, respectively, under DD.

View larger version (17K): [in this window] [in a new window]   Fig. 8. (A) Mean phase of the morning activity peak of the selected and control flies under 12:12 h LD cycle. The mean phase of the morning activity peak was estimated as the time interval between the morning peaks and lights-on, averaged over 10 consecutive cycles. (B) Mean phase of the evening activity peak was estimated as the average time interval between the evening peaks and light-off, averaged over 10 consecutive cycles. Error bars represent 95% confidence intervals (95%CI) around the mean for visual hypothesis testing. A total of early (N=161), control (N=171), and late (N=156) flies were used to estimate the mean phase of the morning and evening activity peaks. (C) The frequency distribution of mean phase of morning, and (d) evening activity peak of the early, control and late populations under 12:12 h LD cycles. Time (h) is plotted along the x-axis and percentage frequency along the y-axis.

View larger version (30K): [in this window] [in a new window]   Fig. 9. Representative locomotor activity plots of individual (A) early, (B) control, and (C) late flies under constant darkness (DD). The vertical dark bars denote activity and their absence indicate rest. Activity for 10 consecutive cycles is plotted along the ordinate and time of the day in hours along the abscissa. (D) Mean circadian period () (h) of the locomotor activity rhythm of the selected and control populations under constant darkness (DD). Error bars represent 95% confidence interval (95%CI) around the mean for visual hypothesis testing. A total of (N=32) early, (N=27) control and (N=37) late flies were used for the estimation of . (E) Frequency distribution of of the locomotor activity rhythm of the early, control and late populations. Time (h) is plotted along the x-axis and percentage frequency along the y-axis.

View larger version (4K): [in this window] [in a new window]   Fig. 10. Correlation between the circadian periods of the locomotor activity and emergence rhythms. The mean values of the locomotor activity and emergence rhythm are plotted along the x and y-axes, respectively.