Data from: Speciation and introgression between Mimulus nasutus and Mimulus guttatus

Mimulus guttatus and M. nasutus are an evolutionary and ecological model sister species pair differentiated by ecology, mating system, and partial reproductive isolation. Despite extensive research on this system, the history of divergence and differentiation in this sister pair is unclear. We present and analyze a population genomic data set which shows that M. nasutus budded from a central Californian M. guttatus population within the last 200 to 500 thousand years. In this time, the M. nasutus genome has accrued genomic signatures of the transition to predominant selfing, including an elevated proportion of nonsynonymous variants, an accumulation of premature stop codons, and extended levels of linkage disequilibrium. Despite clear biological differentiation, we document genomic signatures of ongoing, bidirectional introgression. We observe a negative relationship between the recombination rate and divergence between M. nasutus and sympatric M. guttatus samples, suggesting that selection acts against M. nasutus ancestry in M. guttatus.

沟酸浆（Mimulus guttatus）与鼻花沟酸浆（Mimulus nasutus）是进化与生态学领域的经典模式姊妹物种类群，二者在生态适应性、交配系统（mating system）上存在显著分化，并存在部分生殖隔离（partial reproductive isolation）。尽管该类群已被广泛研究，但其分化历史以及姊妹种间的遗传分化机制仍不明确。本研究报道并分析了一套群体基因组数据集，结果显示：鼻花沟酸浆是在距今20至50万年前，从加州中部的沟酸浆种群中分支演化而来的。在此期间，鼻花沟酸浆的基因组积累了向优势自交转变的标志性基因组特征，包括非同义变异（nonsynonymous variant）比例升高、提前终止密码子（premature stop codon）富集，以及连锁不平衡（Linkage Disequilibrium）水平显著扩展。尽管二者已出现明确的生物学分化，我们仍检测到双向持续进行的基因渐渗（introgression）的基因组信号。我们观察到，重组率（recombination rate）与鼻花沟酸浆和同域分布的沟酸浆样本之间的遗传分化呈负相关关系，这表明在沟酸浆基因组中，源自鼻花沟酸浆的遗传渐渗片段会受到自然选择的排斥。