Data from: Strong premating reproductive isolation drives incipient speciation in Mimulus aurantiacus

Determining which forms of reproductive isolation have the biggest impact on the process of divergence is a major goal of speciation research. These barriers are often divided into those that affect the potential for hybridization (premating isolation), and those that occur after mating (postmating isolation), and much debate has surrounded the relative importance of these categories. Within the species Mimulus aurantiacus, red- and yellow-flowered ecotypes occur in the southwest corner of California, and a hybrid zone occurs where their ranges overlap. We show that premating barriers are exclusively responsible for isolation in this system, with both ecogeographic and pollinator isolation contributing significantly to total isolation. Postmating forms of reproductive isolation have little or no impact on gene flow, indicating that hybrids likely contribute to introgression at neutral loci. Analysis of molecular variation across thousands of RAD-seq markers reveals that the genomes of these taxa are largely undifferentiated. However, structure analysis shows that these taxa are distinguishable genetically, likely due to the impact of loci underlying differentiated adaptive phenotypes. These data exhibit the power of divergent natural selection to maintain highly differentiated phenotypes in the face of gene flow during the early stages of speciation.

明确何种生殖隔离形式对物种分化进程的影响最为显著，是物种形成研究的核心目标之一。生殖隔离屏障通常可划分为两类：一类是影响杂交发生潜力的交配前隔离（premating isolation），另一类是发生于交配后的交配后隔离（postmating isolation），二者的相对重要性长期以来存在诸多学术争议。在橙黄猴面花（*Mimulus aurantiacus*）这一物种中，红花与黄花两种生态型分布于美国加利福尼亚州西南部，二者分布区的重叠区域形成了杂交带。本研究表明，该系统中的生殖隔离完全由交配前隔离介导，生态地理隔离与传粉者隔离均对总隔离度做出了显著贡献。交配后生殖隔离对基因流几乎无影响，这意味着杂种可能会在中性位点发生基因渐渗。对数千个RAD-seq（限制性位点关联DNA测序）标记的分子变异分析显示，这两个类群的基因组整体上未出现明显分化。不过，群体结构分析显示，二者在遗传层面仍可被区分，这可能源于控制适应性分化表型的位点所带来的影响。这些数据证实了在物种形成的早期阶段，即便存在基因流，趋异自然选择仍可维持高度分化的表型。