Data from: Reconciling extremely strong barriers with high levels of gene exchange in annual sunflowers

In several cases, estimates of gene flow between species appears to be higher than predicted given the strength of interspecific barriers. However, as far as we are aware, detailed measurements of reproductive isolation have not previously been compared with a coalescent-based assessment of gene flow. Here, we contrast these two measures in two species of sunflower, Helianthus annuus and Helianthus petiolaris. We quantified the total reproductive barrier strength between these species by compounding the contributions of the following prezygotic and postzygotic barriers: ecogeographic isolation, reproductive asynchrony, immigrant inviability, pollen competition, hybrid seed formation, hybrid seed germination, hybrid pollen fertility, and hybrid seed set. The estimated probabilities that a reproductively successful hybrid is produced: range from 10^-4 to 10^-6 depending on the direction of the cross and the degree of independence among reproductive barriers. Population genetic estimates of gene flow estimated between these sunflower species (N_e m = 0.34-0.76) are due mainly to their large effective population sizes (N_e >10^6). The interspecific migration rate (m) is very small (<10^-7) and an order of magnitude lower than that expected based on our reproductive barrier strength estimates. Thus, even high levels of reproductive isolation (> 0.999) may produce genomic mosaics.

多项研究表明，物种间的基因流（gene flow）估计值往往高于基于种间生殖隔离（reproductive isolation）屏障强度所预测的水平。但据我们所知，此前尚未有研究将生殖隔离的精准测量结果与基于溯祖理论（coalescent theory）的基因流评估进行对比分析。在此，我们以两种向日葵——普通向日葵（Helianthus annuus）与沙地向日葵（Helianthus petiolaris）为研究对象，对这两类指标展开对比。

我们通过整合以下合子前生殖隔离屏障（prezygotic reproductive barrier）与合子后生殖隔离屏障（postzygotic reproductive barrier）的贡献度，量化了这两个物种间的总生殖屏障强度：生态地理隔离（ecogeographic isolation）、生殖异步性（reproductive asynchrony）、迁入者存活障碍（immigrant inviability）、花粉竞争（pollen competition）、杂种种子形成（hybrid seed formation）、杂种种子萌发（hybrid seed germination）、杂种花粉育性（hybrid pollen fertility）以及杂种结实率（hybrid seed set）。可产生具有生殖成功能力的杂种的概率估计值介于10^-4至10^-6之间，具体取值取决于杂交方向以及生殖屏障间的独立程度。

对这两种向日葵间基因流的种群遗传学估计值（有效种群大小与迁移率的乘积，即N_e m = 0.34~0.76），主要源于它们庞大的有效种群大小（effective population size，简称N_e > 10^6）。该物种种间迁移率（m）极低（<10^-7），较基于我们的生殖屏障强度估计值所预期的水平低一个数量级。因此，即便生殖隔离程度极高（>0.999），仍可能形成基因组镶嵌体。