Data from: Evolution of the selfing syndrome: anther orientation and herkogamy together determine reproductive assurance in a self-compatible plant

Capacity for autonomous self-fertilization provides reproductive assurance, has evolved repeatedly in the plant kingdom, and typically involves several changes in flower morphology and development (the selfing syndrome). Yet, the relative importance of different traits and trait combinations for efficient selfing and reproductive success in pollinator-poor environments is poorly known. In a series of experiments, we tested the importance of anther-stigma distance and the less studied trait anther orientation for efficiency of selfing in the perennial herb Arabis alpina. Variation in flower morphology among eight self-compatible European populations was correlated with efficiency of self-pollination and with pollen limitation in a common-garden experiment. To examine whether anther-stigma distance and anther orientation are subject to directional and/or correlational selection, and whether this is because these traits affect pollination success, we planted a segregating F2 population at two native field sites. Selection strongly favored a combination of introrse anthers and reduced anther-stigma distance at a site where pollinator activity was low, and supplemental hand-pollination demonstrated that this was largely because of their effect on securing self-pollination. The results suggest that concurrent shifts in more than one trait can be crucial for the evolution of efficient self-pollination and reproductive assurance in pollinator-poor habitats.

自主自交能力可为植物提供生殖保障，该性状在植物界中多次独立演化，且通常伴随花形态与发育模式的多项改变（即自交综合征（selfing syndrome））。然而，在传粉者匮乏的环境中，不同性状及其组合对高效自交与生殖成功的相对重要性仍鲜为人知。本研究通过一系列实验，针对多年生草本植物高山南芥（Arabis alpina），探究了花药-柱头距离（anther-stigma distance）与此前研究较少的花药朝向（anther orientation）这两个性状对自交效率的影响。在一项同质园实验中，8个欧洲自交亲和种群的花形态变异与自交授粉效率及花粉限制（pollen limitation）显著相关。为探究花药-柱头距离与花药朝向是否受到定向选择或相关选择，且这种选择是否源于这些性状对传粉成功的影响，我们在两个原生境野外站点种植了一个分离的F₂群体。在传粉者活动较低的站点，定向选择显著青睐内向花药与缩小的花药-柱头距离这一性状组合；补充人工授粉实验证实，这一现象主要源于该组合对保障自交授粉的作用。本研究结果表明，在传粉者匮乏的生境中，多个性状的协同演化偏移对高效自交授粉与生殖保障的演化至关重要。