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，是植物界普遍存在的演化过程。这类过程的效应强度受多重合子障碍（zygotic barrier）的调控。此前，这类障碍通常通过费力耗时的人工授粉实验在人工环境中完成量化，但景观尺度下的量化研究仍属空白。本研究借助空间显式模拟框架内的基因流数据，对合子障碍的作用强度进行评估。本研究的模式体系包含欧洲黑杨（Populus nigra）及其天然杂交种加拿大杨（P.× canadensis），二者在自然条件下可发生杂交。研究种群位于德国中部埃德尔河（Eder River）的河漫滩地带。本研究采用逆建模方法，以杂交雄株向单株雌株种子的花粉介导渐渗率作为目标模式。当假设两类类群的花粉竞争能力无差异时，模拟得到的渐渗率与两个类群的观测值均存在显著偏差。引入针对杂交雄株花粉的合子障碍后，上述偏差显著降低。最优模型结果显示，针对花粉介导的渐渗基因流向两个亲本类群——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扩散函数对模型的敏感性进行检验，共使用4种常见概率密度函数，以及一组先前基于本数据集基因流数据拟合得到的花粉扩散函数。结果表明，最优障碍参数值几乎不受本次研究所用扩散函数的影响，且该参数值处于此前人工授粉实验测得的障碍强度区间内，验证了本模型的可靠性。本研究结果证实，逆建模方法是量化隐蔽演化过程的有效手段；我们还探讨了该方法作为研究植物交配系统的重要工具的应用价值，其研究结果可为演化生物学及保育工作中的风险分析提供全新认知视角。