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

Intraspecific 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, Boechera stricta, typically displays white flowers, but some individuals produce purple flowers. We quantified environmental correlates of flower color in natural populations. To disentangle plasticity from genotypic variation, we performed a multiyear field experiment in five gardens. In controlled conditions, we evaluated herbivore preferences and the effects of drought stress and soil pH on flower color expression.
In natural populations, purple-flowered individuals experienced lower foliar herbivory than did their white-flowered counterparts. This pattern also held in the common gardens. Additionally, low-elevation environments induced pigmented flowers (plasticity), and the likelihood of floral pigmentation 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 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.

花颜色的种内变异（intraspecific variation）通常被归因于传粉者介导的选择（pollinator-mediated selection），但这一机制无法解释自交物种中的花颜色多态性（flower color polymorphisms）。由生物胁迫（biotic stresses）与非生物胁迫（abiotic stresses）介导的间接选择，或可维持此类系统中的花颜色变异。

自交草本植物硬毛博克芥（Boechera stricta）通常开白色花，但部分个体可开出紫色花。本研究对自然种群中花颜色的环境关联因子进行了定量分析。为区分表型可塑性（plasticity）与遗传变异（genotypic variation），我们在5个试验园开展了多年野外试验。在可控条件下，我们评估了植食性昆虫的取食偏好，以及干旱胁迫（drought stress）与土壤pH对花颜色表达（flower color expression）的影响。

在自然种群中，开紫色花的个体较开白色花的个体受到的叶片植食性损伤（foliar herbivory）更低。这一规律在同质种植园（common gardens）试验中同样成立。此外，低海拔环境会诱导产生有色花（pigmented flowers），且母本家系（maternal families）的来源海拔越高，其花色素沉着的概率越低，该趋势符合遗传梯度（genetic cline）特征。存活力选择（viability selection）倾向于保留带有花色色素的家系。在实验室条件下，植食性昆虫对开白色花个体的组织造成的损伤显著高于开紫色花的个体。进一步研究发现，干旱会诱导开白色花的谱系（lineages）产生花色色素，而在正常浇水的对照组中，开白色花的植株具有繁殖优势（fecundity advantage）。

自交物种的花颜色变异，可能由植食性压力、干旱胁迫以及其他存在空间异质性的非生物因子共同维持。