Department of Plant and Environmental Sciences, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
Mol Ecol. 2011 Mar;20(6):1155-65. doi: 10.1111/j.1365-294X.2010.04962.x. Epub 2011 Jan 14.
Endogenous circadian rhythms are almost ubiquitous among organisms from cyanobacteria to mammals and regulate diverse physiological processes. It has been suggested that having an endogenous circadian system enables an organism to anticipate periodic environmental changes and adapt its physiological and developmental states accordingly, thus conferring a fitness advantage. However, it is hard to measure fitness directly and there is, to date, only limited evidence supporting the assumption that having a circadian system can increase fitness and therefore be adaptive. In this article, we report an evolutionary approach to examine the adaptive significance of a circadian system. By crossing Arabidopsis thaliana plants containing mutations that cause changes in circadian rhythms, we have created heterozygous 'Mother' (F1) plants with genetic variance for circadian rhythmicity. The segregating F2 offspring present a range of circadian rhythm periods. We have applied a selection to the F2 plants of short and long T-cycles under different competition strengths and found that the average phenotype of circadian period of the resulting F3 plants show a strong positive correlation with the T-cycle growth conditions for the competing F2 plants. Consistent with their circadian phenotypes, the frequency of long-period alleles was altered in the F3 plants. Our results show that F2 plants with endogenous rhythms that more closely match the environmental T-cycle are fitter, producing relatively more viable offspring in the F3 population. Thus, having a circadian clock that matches with the environment is adaptive in Arabidopsis.
内源性昼夜节律几乎存在于从蓝藻到哺乳动物等生物体中,并调节着各种生理过程。有人认为,拥有内源性昼夜节律系统使生物体能够预测周期性的环境变化,并相应地调整其生理和发育状态,从而赋予其适应性优势。然而,很难直接衡量适应性,而且迄今为止,只有有限的证据支持这样的假设,即拥有昼夜节律系统可以提高适应性,从而具有适应性。在本文中,我们报告了一种进化方法来检验昼夜节律系统的适应性意义。通过杂交含有导致昼夜节律变化的突变的拟南芥植物,我们创建了具有遗传变异性的杂合“母亲”(F1)植物,这些植物具有昼夜节律性。分离的 F2 后代呈现出一系列的昼夜节律周期。我们对短和长 T 周期的 F2 植物进行了选择,在不同的竞争强度下,我们发现产生的 F3 植物的平均昼夜节律周期表型与竞争 F2 植物的 T 周期生长条件之间存在强烈的正相关。与它们的昼夜节律表型一致,F3 植物中长周期等位基因的频率发生了改变。我们的研究结果表明,具有更接近环境 T 周期的内源性节律的 F2 植物更具适应性,在 F3 群体中产生相对更多的存活后代。因此,在拟南芥中,具有与环境相匹配的生物钟是适应性的。