Data from: Quantification of the zygotic barrier between interbreeding taxa using gene flow data

Hybridization and introgression via interspecific gene flow are common processes in the plant kingdom. The effectiveness of these processes is governed by the strengths of multiple zygotic barriers. These barriers have often been quantified in artificial settings using laborious and time-consuming hand-pollination experiments, but their quantification is nonexistent at the landscape level. In this study, we utilized gene flow data within a spatially explicit simulation to assess the strengths of zygotic barriers. Our model system consisted of Populusnigra and its hybrid, P.×canadensis, which interbreed under natural conditions. The study population was located in the floodplain of the Eder River in Central Germany. Pollen-mediated introgression rates from hybrid males into the seeds of individual female trees were used as the target pattern using an inverse modeling approach. Simulations that treated pollen from both taxa equally revealed a large discrepancy between the observed and modeled rates of introgression for both taxa. The discrepancy was reduced by introducing a zygotic barrier against the pollen from the hybrid males. The best model outcome indicated comparably strong zygotic barriers acting against pollen-mediated introgressive gene flow into the two parental taxa, P.nigra and P.×canadensis. The sensitivity of our model was tested by applying different dispersal functions. Four common probability density functions were used along with a pollen dispersal function that had previously been fitted to gene flow data from the same dataset. The best barrier value was almost independent of the dispersal functions used here. Moreover, it was within the range previously determined in hand-pollination-based investigations, validating our model. These data indicate that the inverse modeling approach is a powerful method for quantifying hidden processes, and we discuss its use as a valuable tool for generating new insights into plant mating systems that are relevant to evolutionary biology and risk analysis in conservation efforts

通过种间基因流实现的杂交与渐渗，在植物界中是普遍存在的演化过程。这类过程的效应受多重合子障碍（zygotic barrier）的强度调控。这类合子障碍的效应通常通过耗时费力的人工授粉实验，在人工受控环境中得以量化，但在景观尺度上尚缺乏相关定量研究。本研究借助空间显式模拟（spatially explicit simulation）框架内的基因流数据，对合子障碍的强度展开评估。本研究的模式系统选取自然条件下可发生天然杂交的欧洲黑杨（Populus nigra）及其杂交种加拿大杨（P.×canadensis），研究种群位于德国中部埃德尔河（Eder River）的河漫滩地带。本研究采用逆建模（inverse modeling）方法，以杂交雄株向单个雌株种子中发生的花粉介导渐渗率作为目标模式。当假设两类类群的花粉作用等效时开展的模拟结果显示，两类类群的观测渐渗率与模型预测渐渗率之间均存在显著偏差。引入针对杂交雄株花粉的合子障碍后，上述偏差得以显著缩小。最优模型结果表明，针对花粉介导的渐渗基因流向两类亲本类群（欧洲黑杨与加拿大杨）的合子障碍强度相当。本研究通过采用不同的花粉扩散函数，对模型的敏感性展开检验。研究共选用4种常用概率密度函数，以及此前基于本数据集的基因流数据拟合得到的花粉扩散函数。最优合子障碍参数值几乎不受本次研究所用扩散函数的影响，且该参数值落在此前基于人工授粉实验得到的参数区间内，验证了本模型的可靠性。本研究结果表明，逆建模方法是量化隐蔽演化过程的有效手段；我们进一步探讨了该方法作为重要研究工具的应用价值，可为植物交配系统的相关研究提供新视角，相关结论对演化生物学研究及保育工作中的风险分析均具有参考意义。