On the Origin and Implications of Circadian Timekeeping: An Evolutionary Perspective

Nikhil, K. L.; Sharma, Vijay Kumar

doi:10.1007/978-81-322-3688-7_5

Cited by 10 publications

(13 citation statements)

References 211 publications

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“…The majority of life forms on earth exhibit approximately 24-h (circadian) behavioral and physiological rhythms generated by endogenous timekeeping mechanisms-circadian clocks. In addition to driving such endogenous rhythms, circadian clocks facilitate synchronization of organisms' rhythms to daily and seasonal changes in the environment to enhance their survivability, thereby functioning as an adaptive mechanism [1]. The fundamental basis of circadian rhythm generation across all life forms are cell-autonomous molecular oscillators comprising evolutionarily conserved autoregulatory transcription-translation feedback loops [2].…”

Section: Introductionmentioning

confidence: 99%

Heritable gene expression variability and stochasticity govern clonal heterogeneity in circadian period

2020

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A ubiquitous feature of the circadian clock across life forms is its organization as a network of cellular oscillators, with individual cellular oscillators within the network often exhibiting considerable heterogeneity in their intrinsic periods. The interaction of coupling and heterogeneity in circadian clock networks is hypothesized to influence clock's entrainability, but our knowledge of mechanisms governing period heterogeneity within circadian clock networks remains largely elusive. In this study, we aimed to explore the principles that underlie intercellular period variation in circadian clock networks (clonal period heterogeneity). To this end, we employed a laboratory selection approach and derived a panel of 25 clonal cell populations exhibiting circadian periods ranging from 22 to 28 h. We report that a single parent clone can produce progeny clones with a wide distribution of circadian periods, and this heterogeneity, in addition to being stochastically driven, has a heritable component. By quantifying the expression of 20 circadian clock and clock-associated genes across our clone panel, we found that inheritance of expression patterns in at least three clock genes might govern clonal period heterogeneity in circadian clock networks. Furthermore, we provide evidence suggesting that heritable epigenetic variation in gene expression regulation might underlie period heterogeneity.

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Section: Introductionmentioning

confidence: 99%

Heritable gene expression variability and stochasticity govern clonal heterogeneity in circadian period

2020

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“…The adaptive value of circadian clocks for fitness has been demonstrated by diverse strategies that have been nicely reviewed by Vaze and Sharma (2013), Abhilash and Sharma (2016), and Nikhil and Sharma (2017). One of many possible strategies is to investigate whether a trait confers higher adaptive advantage in the context of species competition.…”

Section: Introductionmentioning

confidence: 99%

The Circadian Clock Improves Fitness in the Fruit Fly, Drosophila melanogaster

et al. 2019

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It is assumed that a properly timed circadian clock enhances fitness, but only few studies have truly demonstrated this in animals. We raised each of the three classical Drosophila period mutants for >50 generations in the laboratory in competition with wildtype flies. The populations were either kept under a conventional 24-h day or under cycles that matched the mutant’s natural cycle, i.e., a 19-h day in the case of pers mutants and a 29-h day for perl mutants. The arrhythmic per0 mutants were grown together with wildtype flies under constant light that renders wildtype flies similar arrhythmic as the mutants. In addition, the mutants had to compete with wildtype flies for two summers in two consecutive years under outdoor conditions. We found that wildtype flies quickly outcompeted the mutant flies under the 24-h laboratory day and under outdoor conditions, but perl mutants persisted and even outnumbered the wildtype flies under the 29-h day in the laboratory. In contrast, pers and per0 mutants did not win against wildtype flies under the 19-h day and constant light, respectively. Our results demonstrate that wildtype flies have a clear fitness advantage in terms of fertility and offspring survival over the period mutants and – as revealed for perl mutants – this advantage appears maximal when the endogenous period resonates with the period of the environment. However, the experiments indicate that perl and pers persist at low frequencies in the population even under the 24-h day. This may be a consequence of a certain mating preference of wildtype and heterozygous females for mutant males and time differences in activity patterns between wildtype and mutants.

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“…Moreover, the experimental design lacked any population level replication, a control on pre‐adult density and population size, and information on the maintenance of fly populations on either discrete or continuous generation cycles. This may limit the extent of our interpretations about the evolution of circadian clocks in these flies, as discussed in Nikhil & Sharma (). However, in light of the results reported by Izutsu et al (), one may hypothesize that the DD‐populations from our own laboratory may have also evolved differences in circadian photosensitivity.…”

Section: Evidence From Laboratory Selection Studiesmentioning

confidence: 99%

“…Mutants, as a result of their widely divergent phenotypes, have served as a crucial tool for the identification of molecular‐genetic and neural correlates of circadian clocks in insects (Helfrich‐Förster, ; Hardin, ) (Table ). However, mutants may not be ideal for studying the adaptive value of circadian clocks primarily because inbreeding is known to result in spurious correlations between different measures of fitness, perhaps via random genetic drift (Nikhil & Sharma, ). These challenges therefore restrict the possibility of generalizing the adaptive nature of circadian clocks based on studies on mutants (Table ).…”

Section: How Do We Test Such Hypotheses?mentioning

confidence: 99%

On the relevance of using laboratory selection to study the adaptive value of circadian clocks

Abhilash

Sharma

2016

Physiol. Entomol.

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Abstract. The phrase 'as sure as night comes after day' highlights the most conspicuous phenomenon on earth (i.e. the daily cycling of geophysical factors). It is hypothesized that life-forms on earth have evolved timekeeping mechanisms (circadian clocks) as adaptations to cope with such cyclic variations in their environment and, to test this hypothesis, diverse strategies have been employed. In this review, these different approaches, including comparative, clinal, ecology and/or trait manipulation and laboratory selection strategies are discussed, aiming to evaluate the adaptive value of circadian clocks. The limitations of each of these methods are assessed, and it is suggested that laboratory selection is an ideal, potent and suitable strategy for examining whether circadian clocks are indeed adaptations. In support of this, laboratory selection strategies are highlighted and critically reviewed in a discussion of studies that demonstrate the evolution of circadian clocks and life-history traits in response to selection for the timing of rhythmic behaviours, as well as those studies that demonstrate the evolution of circadian clocks in response to selection for life-history traits. Finally, newer approaches are proposed that involve the use of mutants, simultaneous manipulation of multiple environmental factors and genomic technologies in conjunction with laboratory selection to further explore the adaptive significance of circadian clocks.

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On the Origin and Implications of Circadian Timekeeping: An Evolutionary Perspective

Cited by 10 publications

References 211 publications

Heritable gene expression variability and stochasticity govern clonal heterogeneity in circadian period

Heritable gene expression variability and stochasticity govern clonal heterogeneity in circadian period

The Circadian Clock Improves Fitness in the Fruit Fly, Drosophila melanogaster

On the relevance of using laboratory selection to study the adaptive value of circadian clocks

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