Abstract
Many organisms use free running circadian clocks to anticipate the day night cycle. However, others organisms use simple stimulus-response strategies ('hourglass clocks') and it is not clear when such strategies are sufficient or even preferable to free running clocks. Here, we find that free running clocks, such as those found in the cyanobacterium Synechococcus elongatus and humans, can efficiently project out light intensity fluctuations due to weather patterns ('external noise') by exploiting their limit cycle attractor. However, such limit cycles are necessarily vulnerable to 'internal noise'. Hence, at sufficiently high internal noise, point attractor-based 'hourglass' clocks, such as those found in a smaller cyanobacterium with low protein copy number, Prochlorococcus marinus, can outperform free running clocks. By interpolating between these two regimes in a diverse range of oscillators drawn from across biology, we demonstrate biochemical clock architectures that are best suited to different relative strengths of external and internal noise.
Highlights
Extracting information from a noisy external signal is fundamental to the survival of organisms in dynamic environments (Bowsher and Swain, 2014)
A simple and well-characterized free running clock is that found in S. elongatus where the clock dynamics can be reproduced by the posttranslational dynamics of Kai ABC in vivo as well
We showed that the limit cycle attractor underlying such a clock is able to effectively project out weather-related amplitude changes that are perpendicular to the flat direction of the attractor
Summary
Extracting information from a noisy external signal is fundamental to the survival of organisms in dynamic environments (Bowsher and Swain, 2014). The most remarkable and well-studied examples of clocks are free running circadian clocks, found in organisms ranging from the cyanobacterium S. elongatus to insects, plants and humans Such clocks use non-linear dynamics to generate self-sustained 24-hr rhythms of a preferred amplitude even in the absence of external driving. Some organisms, including humans, have a so-called ‘free-running’ clock that generates a 24-hour rhythm, and keeps ticking even in the absence of any time triggers Others, such as certain cyanobacteria, have an ‘hourglass’ clock that is not self-sustained – rather, these clocks show a simple response to the sunrise (or sunset) that would gradually perish without another sunset (or sunrise). Our work highlights the need to experimentally probe regulatory strategies by varying different kinds of noise independently when possible, since the strategies to deal with different kinds of noise are not equivalent and can be in conflict
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