Mating system variation in hybrid zones: facilitation, barriers and asymmetries to gene flow

Plant mating systems play a key role in structuring genetic variation both within and between species. In hybrid zones, the outcomes and dynamics of hybridization are usually interpreted as the balance between gene flow and selection against hybrids. Yet, mating systems can introduce selective forces that alter these expectations; with diverse outcomes for the level and direction of gene flow depending on variation in outcrossing and whether the mating systems of the species pair are the same or divergent. We present a survey of hybridization in 133 species pairs from 41 plant families and examine how patterns of hybridization vary with mating system. We examine if hybrid zone mode, level of gene flow, asymmetries in gene flow and the frequency of reproductive isolating barriers vary in relation to mating system/s of the species pair. We combine these results with a simulation model and examples from the literature to address two general themes: (i) the two-way interaction between introgression and the evolution of reproductive systems, and (ii) how mating system can facilitate or restrict interspecific gene flow. We conclude that examining mating system with hybridization provides unique opportunities to understand divergence and the processes underlying reproductive isolation.

植物交配系统（plant mating systems）在塑造物种种内与种间的遗传变异结构中发挥关键作用。在杂交带（hybrid zones）中，杂交的结果与动态通常被解读为基因流（gene flow）与对杂交后代的选择之间的平衡。然而，交配系统能够引入改变这一预期的选择压力，基因流的水平与方向会因异交（outcrossing）程度的变异以及物种类对的交配系统是否一致或存在分化而呈现多样的结果。
我们对取自41个植物科的133个物种类对的杂交情况进行了综述，并探究了杂交模式如何随交配系统发生变化。我们检验了杂交带类型、基因流水平、基因流不对称性以及生殖隔离障碍（reproductive isolating barriers）的出现频率是否与物种类对的交配系统存在关联。
我们将上述结果与模拟模型及文献中的案例相结合，以探讨两个核心议题：（i）基因渐渗（introgression）与生殖系统演化之间的双向互作；（ii）交配系统如何促进或限制种间基因流（interspecific gene flow）。
我们认为，将交配系统与杂交现象结合开展研究，为理解物种分化与生殖隔离背后的核心过程提供了独特的契机。