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 <i>Arabidopsis thaliana</i>, 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，这表明内在计时机制在当代种群中具备适应性意义。然而，离散或定量的生物钟变异所带来的性能后果，极少在野外环境中得到验证；不同分离群体对环境的生物钟敏感性尚未被解析，决定演化潜力的统计遗传参数同样未被研究。本研究以拟南芥（Arabidopsis thaliana）为对象开展野外实验，发现通过诱变引发的生物钟周期长度（circadian cycle length，下称生物钟周期（clock period））的显著扰动，会同时降低植株的存活率与繁殖力。通过自然存在的等位基因进行基因组导入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在昼夜周期内时序调控优劣的模型相符，该时序调控亦称为节律相位（phase）。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可相差多达2小时，且周期与相位均表现出显著的遗传方差。通过主成分（principal components, PC）分析对发育速率、植株大小与坐果量等性能指标进行描述后发现，生物钟参数与第一主成分显著相关：略长于24小时的周期与多个RIL群体中更优的性能表现相关联。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中，证实生物钟相位的定量变异对季节变化的非生物因子具有高度响应性；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定量变异均与野外环境中的性能表现相关。