Evidence for Co-Evolution of Masking With Circadian Phase in Drosophila melanogaster
Heritable variation in the timing of daily rhythms gives rise to distinct ‘chronotypes’ in populations. Among humans, the so called ‘lark’ or ‘early birds’ and ‘owl or late’ sleeping phenotypes are easily recognisable Despite its importance, our understanding of how chronotypes are determined is yet unclear. Our artificial laboratory-selection approach has resulted in populations of Drosophila melanogaster which are clearly distinguished as ‘early’ and ‘late’ chronotypes for their timing of eclosion – the act of adults emerging from pupal cases. Recently, we hypothesized that our selection protocol has inadvertently resulted in selection for masking, a non-clock phenomenon, specifically in the ‘early’ chronotype. Our experiments designed to discriminate between enhanced masking to light versus circadian clock mediated changes confirmed our hypothesis that early chronotypes have indeed evolved positive masking, and their apparent entrained phases are largely contributed by masking in addition to evolving advanced phase of circadian entrainment. We provide a systematic experimental approach to examine relative contributions of clock versus non-clock control of an entrained behavior. This is the first experimental demonstration of the evolution of masking as a means of phasing which complements clock control of an entrained behavior.
Ghosh, Arijit, Pragya Sharma, Shephali Dansana, and Vasu Sheeba. “Evidence for Co-Evolution of Masking With Circadian Phase in Drosophila melanogaster.” Journal of Biological Rhythms 36, no. 3 (June 2021): 254–70. https://doi.org/10.1177/0748730421997262.
Schematic of primary experimental design, hypotheses and results. (A) Culture vials were initially placed in 12:12 hr light:dark cycles. On the 11th day, vials with pupae were placed under a light schedule (extended photoperiod) where lights-on happened 3 hours earlier than the day before (left, extended photoperiod) or they went into complete darkness (LD-DD transition). (B) The schematic shows expected pattern of emergence in case of complete circadian clock control (green dashed curve) or masking (blue solid curve). Dark rectangular shades depict duration of darkness. (C-D) Experimentally observed eclosion profiles of the early chronotype populations (blue curves) along with the control unselected populations (dark green curves). (C) early flies show significantly higher emergence than that of control upon encountering an extended photoperiod on assay day 2 (lower panel) compared to previous day (assay day 1, upper panel), showing enhanced masking to lights-on is specific to early flies. (D) When subjected to continuous darkness (assay day 2, lower panel) early flies show significantly higher suppression of eclosion compared to controls suggesting that high emergence of early flies immediately after lights-on was a masking response rather than a clock mediated response. Note y-axis of bottom panel is half of the top panel. Abbreviations: LD = light-dark; DD = constant darkness.
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