Department of Ecology and Genetics, University of Oulu, Oulu, Finland.
Department of Biology, Duke University, Durham, North Carolina, USA.
J Biol Rhythms. 2020 Oct;35(5):452-464. doi: 10.1177/0748730420936408. Epub 2020 Jul 6.
Environmental variation along an elevational gradient can yield phenotypic differentiation resulting from varying selection pressures on plant traits related to seasonal responses. Thus, genetic clines can evolve in a suite of traits, including the circadian clock, that drives daily cycling in varied traits and that shares its genetic background with adaptation to seasonality. We used populations of annual from different elevations in the Sierra Nevada in California to explore among-population differentiation in the circadian clock, flowering responses to photoperiod, and phenological traits (days to cotyledon emergence, days to flowering, and days to seed ripening) in controlled common-garden conditions. Further, we examined correlations of these traits with environmental variables related to temperature and precipitation. We observed that the circadian period in leaf movement was differentiated among populations sampled within about 100 km, with population means varying by 1.6 h. Significant local genetic variation occurred within 2 populations in which circadian period among families varied by up to 1.8 h. Replicated treatments with variable ecologically relevant photoperiods revealed marked population differentiation in critical day length for flowering that ranged from 11.0 to 14.1 h, corresponding to the time period between late February and mid-May in the wild. Flowering time varied among populations in a 14-h photoperiod. Regardless of this substantial population-level diversity, obvious linear clinality in trait variability across elevations could not be determined based on our genotypic sample; it is possible that more complex spatial patterns of variation arise in complex terrains such as those in the Sierra Nevada. Moreover, we did not find statistically significant bivariate correlations between population means of different traits. Our research contributes to the understanding of genetic variation in the circadian clock and in seasonal responses in natural populations, highlighting the need for more comprehensive investigations on the association between the clock and other adaptive traits in plants.
沿海拔梯度的环境变化会导致表型分化，这是由于与季节性反应相关的植物性状受到不同选择压力的影响。因此，遗传梯度可以在一系列性状中进化，包括驱动各种性状日周期变化的生物钟，以及与季节性适应共享其遗传背景的性状。我们使用来自加利福尼亚内华达山脉不同海拔的一年生植物种群，在控制的普通花园条件下探索生物钟、对光周期的开花反应以及表型性状（子叶出现的天数、开花的天数和种子成熟的天数）的种群间分化。此外，我们还检查了这些性状与与温度和降水相关的环境变量的相关性。我们观察到，在大约 100 公里范围内采样的种群中，叶片运动的生物钟周期存在分化，种群平均值相差 1.6 小时。在 2 个种群中，存在显著的本地遗传变异，其中家族间的生物钟周期差异最大可达 1.8 小时。具有可变生态相关光周期的重复处理显示，开花的关键日长存在明显的种群分化，范围从 11.0 到 14.1 小时，对应于野外 2 月下旬到 5 月中旬的时间。在 14 小时光周期中，开花时间在种群之间存在差异。尽管存在这种明显的种群水平多样性，但根据我们的基因型样本，无法确定沿海拔高度的性状变异性的明显线性梯度；在像内华达山脉这样复杂的地形中，可能会出现更复杂的空间变化模式。此外，我们没有发现不同性状的种群平均值之间存在统计学上显著的二元相关性。我们的研究有助于理解自然种群中生物钟和季节性反应的遗传变异，突出了需要更全面地研究生物钟与植物其他适应性性状之间的关系。
