Abstract
BackgroundPrevious studies have implicated a role for circadian clocks in regulating pre-adult development of organisms. Among them two approaches are most notable: 1) use of insects whose clocks have different free-running periods and 2) imposition of artificial selection on either rate of development, timing of emergence or circadian period in laboratory populations. Using these two approaches, influence of clock on rate of development has been elucidated. However, the contribution of circadian clocks in determining time taken for pre-adult development has remained unclear. Here we present results of our studies aimed to understand this influence by examining populations of fruit flies carrying three different alleles of the period gene and hence having different free-running periods. We tried to achieve similarity of genetic background among the three strains while also ensuring that they harbored sufficient variation on loci other than period gene.ResultsWe find that under constant conditions, flies with long period have slower development whereas in presence of light-dark cycles (LD) of various lengths, the speed of development for each genotype is influenced by whether their eclosion rhythms can entrain to them. Under LD 12:12 (T24), where all three strains entrain, they do not show any difference in time taken for emergence, whereas under LD 10:10 (T20) where long period flies do not entrain and LD 14:14 (T28) where short period flies do not entrain, they have slower and faster pre-adult development, respectively, compared to the controls. We also show that a prior stage in development namely pupation is not rhythmic though time taken for pupation is determined by both the environmental cycle and period allele.ConclusionWe discuss how in presence of daily time cues, interaction of the cyclic environmental factors with the clock determines the position and width of the gate available for a fly to emerge (duration of time within a cycle when adult emergence can occur) resulting in an altered developmental duration from that observed under constant conditions. We also discuss the relevance of genetic background influencing this regulation.
Highlights
Previous studies have implicated a role for circadian clocks in regulating pre-adult development of organisms
We show an association between intrinsic period and time to emergence, and further demonstrate that even under the influence of external cycles the variation in time to emergence is dependent on the intrinsic period of the clock as flies which do not entrain are not bound by the eclosion gate imposed by the light-dark cycle and overall development time is different from those that are entrained
The trend observed was similar to that under Constant darkness (DD) i.e., significantly larger time to emergence for perl flies when compared to pers and per+ (p < 0.05; Fig. 1b) while there was no statistically significant difference seen between pers and per+
Summary
Previous studies have implicated a role for circadian clocks in regulating pre-adult development of organisms. Among them two approaches are most notable: 1) use of insects whose clocks have different freerunning periods and 2) imposition of artificial selection on either rate of development, timing of emergence or circadian period in laboratory populations Using these two approaches, influence of clock on rate of development has been elucidated. Oscillations of clock proteins observed in prothoracic gland under light-dark cycles have been found to require inputs from clock neurons in the brain in order to persist under constant conditions [8] Such input from the circadian clock to the prothoracic gland maybe via Prothoracicotrophic Hormone (PTTH) which sets the duration of feeding interval as demonstrated by delayed larval development and increased size of adults that emerge in absence of PTTH [10]. There are multiple, intricate connections between circadian clock, steroidal hormones and developmental processes which interact to regulate timing of adult emergence
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