Data from: Circadian rhythms vary over the growing season and correlate with fitness components

Circadian clocks have evolved independently in all three domains of life, suggesting that internal mechanisms of time-keeping are adaptive in contemporary populations. However, the performance consequences of either discrete or quantitative clock variation have rarely been tested in field settings. Clock sensitivity of diverse segregating lines to the environment remains uncharacterized as do the statistical genetic parameters that determine evolutionary potential. In field studies with Arabidopsis thaliana, we found that major perturbations to circadian cycle length (referred to as clock period) via mutation reduce both survival and fecundity. Subtler adjustments via genomic introgression of naturally occurring alleles indicated that clock periods slightly >24 hrs were adaptive, consistent with prior models describing how well the timing of biological processes is adjusted within a diurnal cycle (referred to as phase). In segregating recombinant inbred lines (RILs), circadian phase varied up to two hours across months of the growing season, and both period and phase expressed significant genetic variances. Performance metrics including developmental rate, size, and fruit set were described by principal components (PC) analyses and circadian parameters correlated with the first PC, such that period lengths slightly >24 hrs were associated with improved performance in multiple RIL sets. These experiments translate functional analyses of clock behavior performed in controlled settings to natural ones, demonstrating that quantitative variation in circadian phase is highly responsive to seasonally variable abiotic factors. The results expand upon prior studies in controlled settings, showing that discrete and quantitative variation in clock phenotypes correlate with performance in nature.

生物钟（circadian clock）在生命的三大域中均独立演化，表明内在的计时机制在当代种群中具有适应性。然而，离散或量化的生物钟表型变异所带来的性能效应，极少在野外环境中得到验证。不同分离株系对环境的生物钟敏感性尚未得到表征，决定演化潜力的统计遗传参数亦是如此。在针对拟南芥（Arabidopsis thaliana）的野外研究中，我们发现通过诱变手段对生物钟周期（clock period）进行大幅扰动，会同时降低其存活率与繁殖力。通过自然存在的等位基因进行基因组渐渗所实现的更细微的节律调整表明，略长于24小时的生物钟周期具有适应性，这与此前描述生物过程时序在昼夜周期内适配程度的模型（该适配程度被称为相位（phase））相符。在分离的重组自交系（recombinant inbred lines, RILs）中，生物钟相位在生长季的不同月份间差异可达两小时，且周期与相位均表现出显著的遗传方差。包括发育速率、个体大小与坐果量在内的性能指标可通过主成分（principal components, PC）分析进行描述，生物钟参数与第一主成分存在相关性，略长于24小时的生物钟周期在多组重组自交系中均与性能提升相关。本实验将受控环境下开展的生物钟行为功能分析拓展至自然环境，证实了生物钟相位的量化变异对季节性变化的非生物因素具有高度响应性。本研究结果拓展了此前受控环境下的相关研究，表明生物钟表型的离散与量化变异均与自然环境中的性能表现存在关联。