Dorn L A, Pyle E H, Schmitt J
Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912, USA.
Evolution. 2000 Dec;54(6):1982-94. doi: 10.1111/j.0014-3820.2000.tb01242.x.
Plants shaded by neighbors or overhead foliage experience both a reduction in the ratio of red to far red light (R:FR), a specific cue perceived by phytochrome, and reduced photosynthetically active radiation (PAR), an essential resource. We tested the adaptive value of plasticity to crowding and to the cue and resource components of foliage shade in the annual plant Arabidopsis thaliana by exposing 36 inbred families from four natural populations to four experimental treatments: (1) high density, full sun; (2) low density, full sun; (3) low density, neutral shade; and (4) low density, low R:FR-simulated foliage shade. Genotypic selection analysis within each treatment revealed strong environmental differences in selection on plastic life-history traits. We used specific contrasts to measure plasticity to density and foliage shade, to partition responses to foliage shade into phytochrome-mediated responses to the R:FR cue and responses to PAR, and to test whether plasticity was adaptive (i.e., in the same direction as selection in each environment). Contrary to expectation, we found no evidence for adaptive plasticity to density. However, we observed both adaptive and maladaptive responses to foliage shade. In general, phytochrome-mediated plasticity to the R:FR cue of foliage shade was adaptive and counteracted maladaptive growth responses to reduced PAR. These results support the prediction that active developmental responses to environmental cues are more likely to be adaptive than are passive resource-mediated responses. Multiple regression analysis detected a few costs of adaptive plasticity and adaptive homeostasis, but such costs were infrequent and their expression depended on the environment. Thus, costs of plasticity may occasionally constrain the evolution of adaptive responses to foliage shade in Arabidopsis, but this constraint may differ among environments and is far from ubiquitous.
被邻居或上层叶片遮荫的植物，会经历红光与远红光比例（R:FR）的降低，这是一种由光敏色素感知的特定信号，同时还会经历光合有效辐射（PAR）的减少，而光合有效辐射是一种必需资源。我们通过将来自四个自然种群的36个自交系家族暴露于四种实验处理下，测试了一年生植物拟南芥对拥挤以及对叶片遮荫的信号和资源成分的可塑性的适应性价值：（1）高密度，全光照；（2）低密度，全光照；（3）低密度，中性遮荫；（4）低密度，低R:FR - 模拟叶片遮荫。每个处理内的基因型选择分析揭示了在对可塑性生活史性状的选择上存在强烈的环境差异。我们使用特定的对比来测量对密度和叶片遮荫的可塑性，将对叶片遮荫的反应分为对R:FR信号的光敏色素介导反应和对PAR的反应，并测试可塑性是否具有适应性（即，与每个环境中的选择方向相同）。与预期相反，我们没有发现对密度具有适应性可塑性的证据。然而，我们观察到了对叶片遮荫的适应性和非适应性反应。一般来说，光敏色素介导的对叶片遮荫的R:FR信号的可塑性是适应性的，并抵消了对PAR减少的非适应性生长反应。这些结果支持了这样的预测，即对环境信号的主动发育反应比被动的资源介导反应更有可能是适应性的。多元回归分析检测到了一些适应性可塑性和适应性稳态的代价，但这些代价并不常见，并且它们的表达取决于环境。因此，可塑性的代价可能偶尔会限制拟南芥对叶片遮荫的适应性反应的进化，但这种限制在不同环境中可能不同，而且远非普遍存在。
