Background and Aims Hybridization is the main driver of plant diversification, and gene flow via hybridization has multifaceted effects on plant evolution. Carex angustisquama is an extremophyte that grows on soils heavily acidified by volcanism. Despite its habitat distinct from that of other species, this species is known to form interspecific hybrids, implying interspecific gene flow. It is crucial to verify the extent and direction of interspecific gene flow between C. angustisquama and closely related species to understand the evolutionary process of an extremophyte in solfatara fields. Methods In this study, expressed sequence tag–simple sequence repeat markers were utilized to infer the extent and direction of interspecific gene flow between C. angustisquama and closely related species. Key Results Bayesian clustering and simulation analyses revealed that all individuals of the three hybrid species were classified into the first hybrid generation or first backcross to C. angustisquama; therefore, current interspecific gene flow is limited. Moreover, in the Bayesian inference of historical gene flow based on multispecies samples, the model that assumed no interspecific gene flow was the most strongly supported across all species pairs, including phylogenetically close but ecologically distinctive species pairs. Conclusions Our results revealed that interspecific gene flow between C. angustisquama and its related species has been limited both currently and historically. Moreover, our results of Bayesian inference of historical gene flow indicated that extrinsic, rather than intrinsic, factors probably act as isolating barriers between Carex species, with hybrid breakdown via microhabitat segregation being the probable potential barrier. Overall, our findings provide insights into the evolutionary process of an extremophyte in solfatara fields and offer an important example of the mechanisms of diversification of the speciose genus Carex.

中文翻译：

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在种间自然杂交下保持的solfatara田中极端植物（Carex angustisquama，莎草科）的物种凝聚力

背景和目的杂交是植物多样化的主要驱动力，通过杂交的基因流动对植物进化具有多方面的影响。Carex angustisquama 是一种极端植物，生长在被火山活动严重酸化的土壤上。尽管它的栖息地与其他物种不同，但已知该物种会形成种间杂种，这意味着种间基因流动。验证 C. angustisquama 和密切相关物种之间的种间基因流动的程度和方向对于了解 solfatara 领域中极端植物的进化过程至关重要。方法 在本研究中，利用表达的序列标签-简单序列重复标记来推断 C. angustisquama 与密切相关物种之间的种间基因流动的程度和方向。主要结果 贝叶斯聚类和模拟分析表明，三个杂交物种的所有个体都被归类为第一杂交代或与 C. angustisquama 的第一回交；因此，目前的种间基因流动是有限的。此外，在基于多物种样本的历史基因流动的贝叶斯推断中，假设没有种间基因流动的模型在所有物种对中得到最强烈的支持，包括系统发育上接近但生态独特的物种对。结论 我们的研究结果表明，C. angustisquama 与其相关物种之间的种间基因流动在当前和历史上都受到限制。此外，我们对历史基因流的贝叶斯推断的结果表明，外在的，而不是内在的，各种因素可能充当了 Carex 物种之间的隔离障碍，通过微生境隔离的杂种分解是可能的潜在障碍。总体而言，我们的研究结果提供了对 solfatara 领域中极端植物进化过程的见解，并提供了一个重要的例子，说明了物种 Carex 属的多样化机制。