Reproductive isolation and the maintenance of species boundaries 1 in two serpentine endemic Jewelflowers

Speciation occurs when reproductive barriers substantially reduce gene flow between lineages. Understanding how specific barriers contribute to reproductive isolation offers insight into the initial forces driving divergence, and the evolutionary and ecological processes responsible for maintaining diversity. Here we quantified multiple pre- and post-pollination isolating barriers in a pair of closely related California Jewelflowers (Streptanthus, Brassicaceae) living in an area of sympatry. S. breweri and S. hesperidis are restricted to similar serpentine habitats, however populations are spatially isolated at fine-scales and rarely co-occur in intermixed stands. Several intrinsic postzygotic barriers were among the strongest we quantified, however postzygotic barriers currently contribute little to overall reproductive isolation due to the cumulative strength of earlier-acting extrinsic barriers, including spatial isolation, and flowering time and pollinator differences. Data fro...物种形成（Speciation）指当生殖屏障显著降低不同谱系间的基因流时所发生的演化过程。阐明特定生殖屏障如何促成生殖隔离，可为解析驱动物种分化的初始动力以及维持生物多样性的演化与生态过程提供重要理论视角。本研究针对一对同域分布（sympatry）的近缘加州链珠花（链珠花属*Streptanthus*，十字花科Brassicaceae），对其多种授粉前（pre-pollination）与授粉后（post-pollination）生殖隔离屏障开展了定量分析。S. breweri与S. hesperidis均局限于相似的蛇纹岩生境（serpentine habitats），但其种群在精细尺度上存在空间隔离，极少在混生群落中共存。本研究定量得到的最强隔离屏障中包含若干内在合子后（postzygotic）隔离屏障，但由于空间隔离、开花物候差异以及传粉者分化等早期作用的外在隔离屏障的累积效应，当前合子后屏障对整体生殖隔离的贡献微乎其微。本研究的相关数据取自……