Evolution of strong reproductive isolation in plants: broad- scale patterns and lessons from a perennial model group

Many recent studies have addressed the mechanisms operating during the early stages of speciation, but surprisingly few studies have tested theoretical predictions on the evolution of strong reproductive isolation. To help address this gap, we first undertook a quantitative review of the hybrid zone literature for flowering plants in relation to reproductive barriers. Then, using Populus as an exemplary model group, we analysed genome wide variation for phylogenetic tree topologies in both early and late stage speciation taxa to determine how these patterns may be related to the genomic architecture of reproductive isolation. Our plant literature survey revealed variation in barrier complexity and an association between barrier number and introgressive gene flow. Focussing on Populus, our genome wide analysis of tree topologies in speciating poplar taxa points to unusually complex genomic architectures of reproductive isolation, consistent with earlier genome wide association studies. These architectures appear to facilitate the escape of introgressed genome segments from polygenic barriers even with strong reproductive isolation, thus affecting their relationships with recombination rates. Placed within the context of the broader literature, our data illustrate how phylogenomic approaches hold great promise for addressing the evolution and temporary breakdown of reproductive isolation during late stages of speciation.

近年来诸多研究聚焦于物种形成（speciation）早期阶段的作用机制，但鲜少有研究对强烈生殖隔离（reproductive isolation）演化的理论预测开展实证检验。为填补这一研究空白，我们首先针对开花植物的杂交带（hybrid zone）相关文献开展定量综述，聚焦生殖障碍（reproductive barriers）相关内容。随后，我们以杨属（Populus）作为典型模式类群，对物种形成早、晚期类群的全基因组变异开展系统发育树拓扑结构分析，以探究这些演化模式与生殖隔离的基因组架构存在何种关联。本次植物文献综述结果显示，生殖障碍的复杂度存在差异，且生殖障碍数量与渐渗基因流（introgressive gene flow）之间存在关联。聚焦杨属的研究中，我们针对正在发生物种形成的杨类群的树拓扑结构开展的全基因组分析显示，其生殖隔离的基因组架构异常复杂，这与此前的全基因组关联研究结果一致。即便存在强烈的生殖隔离，这类基因组架构仍能促进渐渗的基因组片段从多基因障碍中逃逸，进而影响其与重组率之间的关联。结合更广范围的文献背景来看，我们的数据阐明了系统发育基因组学方法在探究物种形成晚期阶段生殖隔离的演化与暂时瓦解方面具有巨大应用前景。