Natural hybridization is frequent in plants and is considered an important factor facilitating speciation. The natural intergeneric hybridization between Ligularia and Cremanthodium was previously confirmed using a couple of DNA markers. However, the mechanism of this intergeneric hybridization and the role of reproductive isolation in the process of hybridization remain unclear. Here we used double-digest restriction site-associated DNA sequencing (ddRAD-seq) to further quantify the occurrence of hybridization, the genetic structure of the hybrid population and the role of reproductive isolation between Ligularia nelumbifolia and Cremanthodium stenoglossum. The results based on the ddRAD-seq SNP data sets indicated that hybridization between L. nelumbifolia and C. stenoglossum was restricted to F1s, and no gene introgression was identified between these two species. STRUCTURE analysis and maximum likelihood (ML) tree results showed a slightly larger genetic contribution of L. nelumbifolia to putative hybrid F1s. We deduced that the reproductive isolation between these two parent species is not well-developed but still strong enough to maintain the genetic integrity of the species, and that their F1s are sterile or with low fertility. Given the poorly resolved phylogenetic relationship between Ligularia and Cremanthodium, the occurrence of natural hybridization between L. nelumbifolia and C. stenoglossum may provide new insights into the re-circumscription and re-delimitation of these two genera.

中文翻译：

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Ligularia nelumbifolia 和 Cremanthodium stenoglossum (Senecioneae, Asteraceae) 之间的自然杂交表明生殖隔离不发达和属间边界模糊

自然杂交在植物中很常见，被认为是促进物种形成的重要因素。Ligularia 和 Cremanthodium 之间的天然属间杂交先前已使用几个 DNA 标记得到证实。然而，这种属间杂交的机制以及生殖隔离在杂交过程中的作用仍不清楚。在这里，我们使用双酶切酶切位点相关 DNA 测序 (ddRAD-seq) 来进一步量化杂交的发生、杂交种群的遗传结构以及在莲叶橐吾和窄舌草之间进行生殖隔离的作用。基于 ddRAD-seq SNP 数据集的结果表明 L. nelumbifolia 和 C. stenoglossum 之间的杂交仅限于 F1s，在这两个物种之间没有发现基因渗入。结构分析和最大似然 (ML) 树结果显示，莲叶莲对假定的杂种 F1 的遗传贡献稍大。我们推断这两个亲本物种之间的生殖隔离并不发达，但仍足以维持物种的遗传完整性，并且它们的 F1 不育或生育力低。鉴于橐吾属和Cremanthodium 之间难以解决的系统发育关系，L. nelumbifolia 和C. stenoglossum 之间的自然杂交的发生可能为这两个属的重新界定和重新定界提供新的见解。nelumbifolia 到假定的杂种 F1。我们推断这两个亲本物种之间的生殖隔离并不发达，但仍足以维持物种的遗传完整性，并且它们的 F1 不育或生育力低。鉴于橐吾属和Cremanthodium 之间难以解决的系统发育关系，L. nelumbifolia 和C. stenoglossum 之间的自然杂交的发生可能为这两个属的重新界定和重新定界提供新的见解。nelumbifolia 到假定的杂种 F1。我们推断这两个亲本物种之间的生殖隔离并不发达，但仍足以维持物种的遗传完整性，并且它们的 F1 不育或生育力低。鉴于橐吾属和Cremanthodium 之间难以解决的系统发育关系，L. nelumbifolia 和C. stenoglossum 之间的自然杂交的发生可能为这两个属的重新界定和重新定界提供新的见解。