Evolution of circadian rhythms in Drosophila melanogaster populations reared in constant light and dark regimes for over 330 generations

Feb 4, 2017Chronobiology international

Changes in daily activity patterns of fruit flies raised in constant light or darkness for over 330 generations

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Abstract

Drosophila melanogaster populations evolving under constant darkness for over 19 years exhibit significantly higher robustness in circadian rhythms compared to those evolving under constant light.

Circadian rhythms persist in D. melanogaster populations maintained in both constant light and constant darkness without differences in circadian period.
Entrained rhythms in constant light and constant darkness differ from those in rhythmic environments.
Constant darkness is associated with the evolution of more robust free-running activity-rest and adult emergence rhythms.
This robustness may suggest an adaptive advantage of circadian clocks or related functions of clock genes in other traits.

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Organisms are believed to have evolved circadian clocks as adaptations to deal with cyclic environmental changes, and therefore it has been hypothesized that evolution in constant environments would lead to regression of such clocks. However, previous studies have yielded mixed results, and evolution of circadian clocks under constant conditions has remained an unsettled topic of debate in circadian biology. In continuation of our previous studies, which reported persistence of circadian rhythms in Drosophila melanogaster populations evolving under constant light, here we intended to examine whether circadian clocks and the associated properties evolve differently under constant light and constant darkness. In this regard, we assayed activity-rest, adult emergence and oviposition rhythms of D. melanogaster populations which have been maintained for over 19 years (~330 generations) under three different light regimes - constant light (LL), light-dark cycles of 12:12 h (LD) and constant darkness (DD). We observed that while circadian rhythms in all the three behaviors persist in both LL and DD stocks with no differences in circadian period, they differed in certain aspects of the entrained rhythms when compared to controls reared in rhythmic environment (LD). Interestingly, we also observed that DD stocks have evolved significantly higher robustness or power of free-running activity-rest and adult emergence rhythms compared to LL stocks. Thus, our study, in addition to corroborating previous results of circadian clock evolution in constant light, also highlights that, contrary to the expected regression of circadian clocks, rearing in constant darkness leads to the evolution of more robust circadian clocks which may be attributed to an intrinsic adaptive advantage of circadian clocks and/or pleiotropic functions of clock genes in other traits.

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Evolution of circadian rhythms in Drosophila melanogaster populations reared in constant light and dark regimes for over 330 generations

Abstract

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