Breakdown of selection-mediated correlation between development time and clock period

- Selection for faster development shortened circadian clock period (τ) by ~ 0.5-h.
- Exposure to LD and WC cycles elicits after-effect.
- Exposure to LD and WC cycles breaks-down correlation between development time and circadian clocks.

Previously we have reported that selection for faster pre-adult development in fruit flies speeded-up development by ~ 29-h and shortened the clock period (τ) by ~ 0.5 h, which suggests that development time and τ are correlated. Since it is known that τ is altered following exposure to light/dark (LD) cycles, we asked whether this correlation persists in the faster developing (FD) and control (BD) flies by examining the τ of the activity/rest rhythm and its difference between the two stocks following exposure to a variety of cyclic conditions. We assayed the activity/rest behavior of FD and BD flies under DD, following a week-long exposure to (a) LD cycles of 10:10 h, 12:12 h and 14:14 h, or (b) LD12:12 h with different light intensities (10, 100 and 1000 lx), or (c) 12:12 h warm/cold (WC) cycles of 25:18 °C (WC1) and 29:25 °C (WC2), or (d) WC1 or WC2, in-phase or out-of-phase with LD. The results revealed that both LD and WC altered the τ of FD and BD flies, and considerably reduced the selection-mediated difference between the two stocks. LD10:10 caused more severe after-effects on τ compared to LD12:12 and LD14:14. Among the WC cycles, WC1 which had a higher contrast caused period shortening. Irrespective of the phase relationship, imposition of LD cycles on WC cycles made no difference to the extent of after-effects; however, interestingly there was a reversal in the trend, in that, now WC2 with LD caused most drastic reduction in τ. These results suggest that cyclic environments modulate the circadian organization of Drosophila melanogaster altering the selection-mediated correlation between pre-adult development time and clock period.