Data from: Can plants evolve tolerance mechanisms to heterospecific pollen effects? An experimental test of the adaptive potential in Clarkia species

Flowering plants do not occur alone and often grow in mixed-species communities where pollinator sharing is high and interactions via pollinators can occur at pre- and post-pollination stages. While the causes and consequences of pre-pollination interactions have been well studied little is known about post-pollination interactions via heterospecific pollen (HP) receipt, and even less about the evolutionary implications of these interactions. In particular, the degree to which plants can evolve tolerance mechanisms to the negative effects of HP receipt has received little attention. Here, we aim to fill this gap in our understanding of post-pollination interactions by experimentally testing whether two co-flowering Clarkia species can evolve HP tolerance, and whether tolerance to specific HP ‘genotypes’ (fine-scale local adaptation to HP) occurs. We find that Clarkia species vary in their tolerance to HP effects. Furthermore, conspecific pollen performance and the magnitude of HP effects were related to the recipient’s history of exposure to HP in C. xantiana but not in C. speciosa. Specifically, better conspecific pollen performance and smaller HP effects were observed in populations of C. xantiana plants with previous exposure to HP compared to populations without such exposure. These results suggest that plants may have the potential to evolve tolerance mechanisms to HP effects but that these may occur not from the female (stigma, style) but from the male (pollen) perspective, a possibility that is often overlooked. We find no evidence for fine-scale local adaptation to HP receipt. Studies that evaluate the adaptive potential of plants to the negative effects of HP receipt are an important first step in understanding the evolutionary consequences of plant-plant post-pollination interactions. Such knowledge is in turn crucial for deciphering the role of plant–pollinator interactions in driving floral evolution and the composition of co-flowering communities.

显花植物极少单一生长，常共存于多物种群落中，此类群落传粉者共享现象普遍，且植物间可通过传粉者发生授粉前与授粉后互作。尽管授粉前互作的成因与后果已得到充分研究，但学界对异种花粉（heterospecific pollen, HP）接收介导的授粉后互作仍所知甚少，对这类互作的进化意义更是了解有限。尤其值得关注的是，植物演化出抵御异种花粉负面效应的耐受机制的程度，相关研究极少。本研究旨在填补这一认知空白，通过实验检验两种同花期克拉克属（Clarkia）植物能否演化出异种花粉耐受能力，以及对特定异种花粉“基因型”的耐受能力（即对异种花粉的精细尺度本地适应）是否存在。研究发现，不同克拉克属植物对异种花粉效应的耐受程度存在差异。此外，在黄花克拉克草（C. xantiana）中，同种花粉的发育表现与异种花粉效应的强度，与受体种群此前接触异种花粉的历史相关；而在艳克拉克草（C. speciosa）中则无此关联。具体而言，相较于未接触过异种花粉的种群，曾暴露于异种花粉的黄花克拉克草种群，其同种花粉发育表现更佳，异种花粉带来的负面效应也更弱。这些结果表明，植物或具备演化出抵御异种花粉负面效应的耐受机制的潜力，但这类耐受机制可能并非源自雌性生殖器官（柱头、花柱），而是从雄性（花粉）层面产生——这一可能性常被忽视。本研究未发现植物对异种花粉接收存在精细尺度本地适应的证据。评估植物应对异种花粉负面效应的适应潜力的研究，是理解植物间授粉后互作进化后果的重要第一步。这类认知反过来也对解析植物-传粉者互作在驱动花部演化及同花期群落组成中的作用至关重要。