Ecological causes and consequences of flower color polymorphism in a self-pollinating plant (Boechera stricta)

Intraspecific (种内的) variation in flower color is often attributed to pollinator-mediated selection, yet this mechanism cannot explain flower color polymorphisms in self-pollinating species. Indirect selection mediated via biotic and abiotic stresses could maintain flower color variation in these systems. The selfing forb (草本植物), Boechera stricta, typically displays white flowers, but some individuals produce purple flowers. We quantified environmental correlates of flower color in natural populations. To disentangle (解开) plasticity from genotypic variation, we performed a multiyear field experiment in five gardens. In controlled conditions, we evaluated herbivore (食草动物) preferences and the effects of drought stress and soil pH on flower color expression. In natural populations, purple-flowered individuals experienced lower foliar (叶的) herbivory than did their white-flowered counterparts (对应的事物). This pattern also held in the common gardens. Additionally, low-elevation (低海拔) environments induced pigmented flowers (plasticity), and the likelihood (可能性) of floral pigmentation (花色素) decreased with source elevation of maternal families (genetic cline). Viability selection favored families with pigmented flowers. In the laboratory, herbivores exerted greater damage on tissue derived from white- vs purple-flowered individuals. Furthermore, drought induced pigmentation in white-flowered lineages, and white-flowered plants had a fecundity (繁殖力) advantage in the well-watered control. Flower color variation in selfing species is probably maintained by herbivory, drought stress, and other abiotic factors that vary spatially.

植物花色的种内变异大多是由授粉者介导的选择所引起的，而这种机理不能用来解释自交授粉物种的花色形态多样性。通过生物和非生物胁迫的间接选择可以维持这些自交授粉物种中的花色变异。十字花科的草本Boechera stricta是自交植物的典型代表，其大部分的个体是开白色花，而有少部分的个体是开紫色花。本文对自然群体中花色变异中的环境相关进行了定量分析。为了区分开遗传变异对于花色可塑性的影响，作者在5个实验苗圃中进行了多年的田间试验。在控制的环境条件下，作者评估了食草动物的喜好性，以及干旱胁迫和土壤PH值对于花色的影响。在自然群体中，相比于开白花的个体，开紫花的个体遭受了更低的叶面啃食。这个模式同样适用于实验苗圃中。另外，低海拔的环境会诱导有颜色的花（表型可塑），而花有颜色的可能性随着其母本来源海拔高度的降低逐渐减小（遗传因素）。生活力试验显示带有颜色的花的生长发育更加具有优势。在实验室条件下，相比于开紫花的个体，食草动物对来自于白花个体的组织会造成更大的伤害。此外，干旱会诱导白花品系中色素的积累，并且白花的个体在水分充足的情况下繁殖力具有优势。自交植物中的花色变异可能会受到食草动物、干旱胁迫以及其它的一些空间上存在变异的非生物因子的影响。

通讯：Jill T. Anderson (https://www.genetics.uga.edu/directory/jill-anderson)

研究方向：演化遗传学：环境对于植物性状表达、自然选择及区域适应的影响；植物种子传播等。

doi: 10.1111/nph.14998