Evidence for Co-Evolution of Masking With Circadian Phase inDrosophila Melanogaster

Abstract

Heritable variation in the timing of rhythmic events with respect to daily time cues gives rise to chronotypes. Despite its importance, the mechanisms (clock or non-clock) regulating chronotypes remain elusive. Using artificial laboratory selection for divergent phasing of emergence of adults from pupae, our group has derived populations of Drosophila melanogaster which are early and late chronotypes for eclosion rhythm. Several circadian rhythm characteristics of these populations have since been described. We hypothesized that our selection protocol has inadvertently resulted in selection for masking, a non-clock phenomenon, in the early chronotype due to the placement of our selection window (which includes the lights-ON transition). We designed experiments to discriminate between enhanced masking to light versus circadian clock mediated changes in determining enhanced emergence in the morning window in our early chronotypes. Using a series of phase-shift protocols, LD-DD transition, and T-cycle experiments, we find that our early chronotypes have evolved positive masking, and their apparent entrained phases are largely contributed by masking. Through skeleton T-cycle experiments, we find that in addition to the evolution of greater masking, our early chronotypes have also evolved advanced phase of entrainment. Furthermore, our study systematically outlines experimental approaches to examine relative contributions of clock versus non-clock control of an entrained behavior. Although it has previously been suggested that masking may confer an adaptive advantage to organisms, here we provide experimental evidence for the evolution of masking as a means of phasing that can complement clock control of an entrained behavior.

Keep Your Mask On: The Benefits of Masking for Behavior and the Contributions of Aging and Disease on Dysfunctional Masking Pathways

“…In this way, the masking system is capable of overriding the internal circadian rhythm so that the organism can escape danger. In fact, masking behavior has recently been shown to be evolutionarily conserved in Drosophila melanogaster ( Ghosh et al, 2021 ), providing further evidence that masking provides an adaptive advantage for the organism. Importantly, masking can also be complementary to entrainment when the environmental changes are predictable.…”

“…The ability to respond immediately to changes in exogenous stimuli is adaptive to the organism, as it allows the organism to behave in appropriate ways, depending on the organism’s temporal niche ( Lu et al, 2010 ; Bloch et al, 2013 ; Ghosh et al, 2021 ). For example, nocturnal (i.e., night-active) organisms mask negatively to powerful exogenous stimuli, such as light, by decreasing activity, and they mask positively to darkness by increasing activity ( Aschoff and von Goetz, 1988a ; Aschoff, 1999 ; Shuboni et al, 2012 ).…”