Data from: Sibling competition arena: selfing and a competition arena can combine to constitute a barrier to gene flow in sympatry

Closely-related species coexisting in sympatry provide critical insight into the mechanisms underlying speciation and the maintenance of genetic divergence. Selfing may promote reproductive isolation by facilitating local adaptation, causing reduced hybrid fitness in parental environments. Here, we propose a novel mechanism by which selfing can further impair interspecific gene flow: selfing may act to ensure that non-hybrid progeny systematically co-occur whenever hybrid genotypes are produced. Under a competition arena, the fitness differentials between non-hybrid and hybrid progeny are then magnified, preventing development of interspecific hybrids. We investigate whether this “sibling competition arena” can explain the coexistence in sympatry of closely-related species of the plant fungal pathogens (Microbotryum) causing anther-smut disease. The probabilities of intra-promycelial mating (automixis), outcrossing, and sibling competition were manipulated in artificial inoculations to evaluate their contribution to reproductive isolation. We report that both intra-promycelial selfing and sibling competition significantly reduced rates of hybrid infection beyond that expected based solely upon selfing rates and non-competitive fitness differentials between hybrid and non-hybrid progeny. Our results thus suggest that selfing and a sibling competition arena can combine to constitute a barrier to gene flow and diminish selection for additional barriers to gene flow in sympatry.同域共存的近缘物种，可为物种形成与遗传分化维持的内在机制提供关键研究视角。自交可通过促进本地适应，在亲本环境中降低杂交后代的适合度，从而推动生殖隔离的形成。本研究提出一种可进一步削弱种间基因流的全新自交作用机制：当杂交基因型产生时，自交可确保非杂交后代始终与其共存。在竞争场景下，非杂交与杂交后代间的适合度差异会被放大，从而阻碍种间杂交后代的发育。本研究针对该“同胞竞争场景”展开探究，验证其能否解释引发花药黑粉病的植物病原真菌——微球黑粉菌属（Microbotryum）近缘物种在同域环境下的共存现象。本研究通过人工接种实验，对菌丝内交配（自体受精，automixis）、异交以及同胞竞争的发生概率进行调控，以此评估它们对生殖隔离的贡献程度。研究结果表明，相较于仅基于自交率以及杂交与非杂交后代间非竞争性适合度差异所预测的结果，菌丝内自交与同胞竞争均可显著降低杂交感染率。综上，本研究结果显示，自交与同胞竞争场景可共同构成基因流的阻隔屏障，并削弱同域环境下对额外基因流阻隔机制的选择压力。