Abstract
Here we report the results of a study aimed at examining stability of adult emergence and activity/rest rhythms under semi-natural conditions (henceforth SN), in four large outbred fruit fly Drosophila melanogaster populations, selected for emergence in a narrow window of time under laboratory (henceforth LAB) light/dark (LD) cycles. When assessed under LAB, selected flies display enhanced stability in terms of higher amplitude, synchrony and accuracy in emergence and activity rhythms compared to controls. The present study was conducted to assess whether such differences in stability between selected and control populations, persist under SN where several gradually changing time-cues are present in their strongest form. The study revealed that under SN, emergence waveform of selected flies was modified, with even more enhanced peak and narrower gate-width compared to those observed in the LAB and compared to control populations in SN. Furthermore, flies from selected populations continued to exhibit enhanced synchrony and accuracy in their emergence and activity rhythms under SN compared to controls. Further analysis of zeitgeber effects revealed that enhanced stability in the rhythmicity of selected flies under SN was primarily due to increased sensitivity to light because emergence and activity rhythms of selected flies were as stable as controls under temperature cycles. These results thus suggest that stability of circadian rhythms in fruit flies D. melanogaster, which evolved as a consequence of selection for emergence in a narrow window of time under weak zeitgeber condition of LAB, persists robustly in the face of day-to-day variations in cycling environmental factors of nature.
Highlights
Circadian rhythms are manifestation of an organism’s temporal adaptation to daily changes in cyclic environmental conditions
We elucidated effect of semi-natural conditions on the stability of daily rhythms in D. melanogaster populations selected for emergence in a narrow window of time
In a previous study we had shown that such selection eliminated flies from both ends of the emergence waveform and favoured those that emerged during the selection window, and this eventually resulted in the evolution of increased stability in emergence and activity rhythms [21]
Summary
Circadian rhythms are manifestation of an organism’s temporal adaptation to daily changes in cyclic environmental conditions. The major differences in emergence rhythm between semi-natural (SN) and laboratory (LAB) conditions include much narrower emergence gate-width and reduced nighttime emergence in SN along with the finding that rhythmicity in emergence is rescued in genetically arrhythmic period null (per0) flies [14] From these studies it is clear that several aspects of daily rhythms differ between natural and laboratory conditions. Early-late chronotypes persisted in these populations, under semi-natural conditions the phenotypes became even more striking, and showed no correlation with natural morning and evening transitions, unlike that observed under laboratory conditions Such differential effect of LAB versus SN on the phase of emergence makes it relevant to ask how stability of circadian rhythms is influenced by the presence of multiple gradually changing zeitgebers of nature
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