Life-history traits of Drosophila melanogaster populations exhibiting early and late eclosion chronotypes

Abstract

BackgroundThe hypothesis that circadian clocks confer adaptive advantage to organisms has been proposed based on its ubiquity across almost all levels of complexity and organization of life-forms. This thought has received considerable attention, and studies employing diverse strategies have attempted to investigate it. However, only a handful of them have examined how selection for circadian clock controlled rhythmic behaviors influences life-history traits which are known to influence Darwinian fitness. The ‘early’ and ‘late’ chronotypes are amongst the most widely studied circadian phenotypes; however, life-history traits associated with these chronotypes, and their consequences on Darwinian fitness remain largely unexplored, primarily due to the lack of a suitable model system. Here we studied several life-history traits of Drosophila melanogaster populations that were subjected to laboratory selection for morning (early) and evening (late) emergence.ResultsWe report that the late eclosion chronotypes evolved longer pre-adult duration as compared to the early eclosion chronotypes both under light/dark (LD) and constant dark (DD) conditions, and these differences appear to be mediated by both clock dependent and independent mechanisms. Furthermore, longer pre-adult duration in the late chronotypes does not lead to higher body-mass at pupariation or eclosion, but the late females were significantly more fecund and lived significantly shorter as compared to the early females.ConclusionsCoevolution of multiple life-history traits in response to selection on timing of eclosion highlights correlations of the genetic architecture governing timing of eclosion with that of fitness components which suggests that timing ecologically relevant behaviors at specific time of the day might confer adaptive advantage.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0622-3) contains supplementary material, which is available to authorized users.

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

“…Pigment dispersing factor (PDF) levels (a neuropeptide that orchestrates circadian rhythms; Helfrich‐Förster, ) were also assessed to test the hypothesis of weakly coupled oscillator network in ‘late’ populations. It was found that, in accordance with their emergence chronotypes, the phases of per , tim , clk , vri and PDF oscillation in ‘early’ and ‘late’ populations have diverged, with the mRNA and neuropeptide levels peaking earlier in ‘early’ populations relative to ‘late’ populations (Nikhil et al , ). Furthermore, amplitude and levels of mRNA and PDF oscillations have also diverged between these two populations (Nikhil et al , ).…”

“…As a correlated response to selection, ‘early’ and ‘late’ populations showed divergence in the τ of eclosion and activity/rest rhythms, exhibiting shorter and longer τ , respectively (Fig. b; Kumar et al , ; Nikhil et al , ). Furthermore, ‘early’ and ‘late’ populations evolved divergent PRCs (Kumar et al , ) and light requirement schedules for entrainment (Vaze et al , ) of the eclosion rhythm.…”

“…Consequently, the ψ of the eclosion rhythm of ‘early’ and ‘late’ populations has diverged by 4–5 h under laboratory LD cycles (Fig. c) (Kumar et al , ; Nikhil et al , ). Furthermore, it was observed that this divergence was enhanced greatly under semi‐natural conditions (Vaze et al , ) and this was eventually shown to be driven primarily by temperature cycles (Nikhil et al , ), thereby indicating the evolution of a more fundamental clock feature, common to both light and temperature entrainment, that drives the timing of behaviour.…”

“…(); (a, top) Vaze & Sharma (); (a, bottom; b) Yadav & Sharma (); (b, c) Nikhil et al . (); and (d) Nikhil et al . ().…”

“…Furthermore, amplitude and levels of mRNA and PDF oscillations have also diverged between these two populations (Nikhil et al , ). These results are taken to suggest that, because vri (apart from being an output molecule) also regulates per and tim mRNA expression (Hardin, ), selection on the timing of eclosion probably drove the divergence of vri oscillation, which in turn may have caused the divergence of the core molecular clockwork between ‘early’ and ‘late’ populations (Nikhil et al , ) thus highlighting the possible ways in which selection on ψ of a circadian behaviour might drive the evolution of underlying circadian clocks.…”