A goal of speciation genetics is to understand how the genetic components underlying interspecific reproductive barriers originate within species. Unilateral incompatibility (UI) is a postmating prezygotic barrier in which pollen rejection in the female reproductive tract (style) occurs in only one direction of an interspecific cross. Natural variation in the strength of UI has been observed among populations within species in the wild tomato clade. In some cases, molecular loci underlying self-incompatibility (SI) are associated with this variation in UI, but the mechanistic connection between these intra- and inter-specific pollen rejection behaviors is poorly understood in most instances. We generated an F2 population between SI and SC genotypes of a single species, Solanum pennellii, to examine the genetic basis of intraspecific variation in UI against other species, and to determine whether loci underlying SI are genetically associated with this variation. We found that F2 individuals vary in the rate at which UI rejection occurs. One large effect QTL detected for this trait co-localized with the SI-determining S-locus. Moreover, individuals that expressed S-RNase-the S-locus protein involved in SI pollen rejection-in their styles had much more rapid UI responses compared to those without S-RNase protein. Our analysis shows that intraspecific variation at mate choice loci-in this case at loci that prevent self-fertilization-can contribute to variation in the expression of interspecific isolation, including postmating prezygotic barriers. Understanding the nature of such intraspecific variation can provide insight into the accumulation of these barriers between diverging lineages.

中文翻译：

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野生番茄进化枝（Sol​​anum sect. Lycopersicon）中种间交配后生殖障碍的种内遗传变异

物种形成遗传学的一个目标是了解种间生殖障碍背后的遗传成分如何起源于物种内部。单侧不相容性 (UI) 是一种后交配前屏障，其中雌性生殖道（样式）中的花粉排斥仅发生在种间杂交的一个方向上。在野生番茄进化枝的物种内的种群中观察到 UI 强度的自然变化。在某些情况下，自身不相容性 (SI) 的分子位点与 UI 的这种变化有关，但在大多数情况下，人们对这些种内和种间花粉排斥行为之间的机制联系知之甚少。我们在单一物种 Solanum pennellii 的 SI 和 SC 基因型之间生成了 F2 种群，检查 UI 与其他物种的种内变异的遗传基础，并确定 SI 潜在的位点是否与这种变异在遗传上相关。我们发现 F2 个体发生 UI 拒绝的速度各不相同。针对该性状检测到的一个大效应 QTL 与 SI 确定 S 基因座共定位。此外，与那些没有 S-RNase 蛋白的人相比，在他们的风格中表达 S-RNase（参与 SI 花粉排斥的 S 位点蛋白）的个体具有更快的 UI 反应。我们的分析表明，配偶选择基因座的种内变异 - 在这种情况下是阻止自我受精的基因座 - 可以导致种间隔离表达的变异，包括交配后的前屏障。