Burghardt Liana T, Metcalf C Jessica E, Donohue Kathleen
Department of Biology, Duke University, Box 90338 Durham, North Carolina 27708 USA
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544 USA.
Am J Bot. 2016 Jan;103(1):47-59. doi: 10.3732/ajb.1500286. Epub 2016 Jan 7.
Understanding the factors shaping range limits is critical given current changes in climate as well as human-mediated introduction of species into novel environments. Phenological responses to climate influence range limits by allowing plants to avoid conditions that decrease population growth rates. Studying these processes is a challenge due to the joint contributions of both genetic and environmental variation to phenology.
Using a previously developed model that predicts phenology of three dormancy "genotypes" in four locations spanning the European range of Arabidopsis thaliana, we examined how variation in seed dormancy influences the environmental conditions experienced by reproductive individuals and how those conditions influence reproductive potential. We calculated two metrics: temperature experienced during reproduction and the length of thermal window available for reproduction.
Seed dormancy levels determine whether a spring-flowering life cycle is expressed and thus determine the reproductive environment. A genetic cline in seed dormancy across the range reduces differences in reproductive environment and increases the thermal opportunity for reproduction before conditions become unfavorable for survival. Counter-intuitively, these putatively local genotypes are predicted to reproduce in slightly cooler conditions in the south than in the north, suggesting that maternal environmental effects on average could induce deeper dormancy in southern seeds reinforcing the observed genetic cline. However, within a location, we found large individual level differences.
Phenological adjustments of early life stages can contribute to the maintenance of consistent reproductive environments experienced by individual plants across ranges despite variable environmental conditions over time and space.
鉴于当前的气候变化以及人类将物种引入新环境的行为，了解影响分布范围界限的因素至关重要。植物对气候的物候响应通过使植物避开降低种群增长率的条件来影响分布范围界限。由于遗传和环境变异对物候的共同作用，研究这些过程具有挑战性。
利用先前开发的一个模型，该模型预测了拟南芥在欧洲分布范围内四个地点的三种休眠“基因型”的物候，我们研究了种子休眠的变异如何影响生殖个体所经历的环境条件，以及这些条件如何影响生殖潜力。我们计算了两个指标：生殖期间经历的温度和可用于生殖的热窗口长度。
种子休眠水平决定了是否表现出春季开花的生命周期，从而决定了生殖环境。分布范围内种子休眠的遗传渐变减少了生殖环境的差异，并在条件变得不利于生存之前增加了生殖的热机会。与直觉相反，这些假定的本地基因型预计在南方比在北方稍凉的条件下繁殖，这表明母体环境平均效应可能会使南方种子的休眠更深，从而加强观察到的遗传渐变。然而，在一个地点内，我们发现个体水平存在很大差异。
尽管随着时间和空间环境条件变化，但早期生命阶段的物候调整有助于维持个体植物在整个分布范围内所经历的一致生殖环境。
