BACKGROUND AND AIMS Hybridization is known to drive plant speciation through the establishment of homoploid or allopolyploid hybrid species. Here we investigate the origin of Pulmonaria helvetica, a narrow endemic species described across a restricted area of Switzerland that was entirely covered by ice during the last glacial maximum. This species presents an original number of chromosomes (2n = 24) and morphological traits suggestive of a hybrid origin. METHODS We sequenced a plastid locus and 1077 double-digest restriction site associated DNA (ddRAD) loci in 67 individuals from across the distribution range of P. helvetica and candidate progenitor species growing in the same area. Assignment of genotypes to main genetic clusters within and among taxa using STRUCTURE tested whether P. helvetica represents a genetically differentiated lineage and addressed the hypothesis of its hybrid origin. Comparative ecological modelling further addressed possible niche differentiation among taxa. KEY RESULTS P. helvetica was highlighted as a genetically homogeneous species distinct from co-occurring taxa. Consistent with a scenario of hybrid speciation, it presented clear evidence of balanced admixture between P. officinalis (2n = 16) and P. mollis s.l. (2n = 18, 22) that was also highlighted as maternal progenitor based on plastid sequences. Limited genetic structure within the maternal progenitor is consistent with an origin of P. helvetica through either homoploid hybridization with considerable karyotype changes or via complex scenarios of allopolyploidy involving a dysploid taxon of P. mollis s.l. Comparative niche modelling indicated non-significant ecological differences between P. helvetica and its progenitors, supporting intrinsic factors resulting from hybridization as main drivers of speciation. CONCLUSIONS Hybridization appears as a major process having promoted the postglacial origin of the narrow endemic P. helvetica, suggesting hybrid speciation as an effective process that rapidly produces new species under climate changes.

中文翻译：

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狭长的地方性 Pulmonaria helvetica 起源的最近杂交物种形成

背景和目的 已知杂交通过建立同倍体或异源多倍体杂种物种来推动植物物种形成。在这里，我们调查了 Pulmonaria helvetica 的起源，这是一种狭窄的地方性物种，在瑞士的一个限制区域内被描述，在最后一次冰期最大值期间完全被冰覆盖。该物种呈现出原始数量的染色体 (2n = 24) 和暗示杂种起源的形态特征。方法我们对来自同一地区生长的瑞士黑体菌和候选祖先物种分布范围内的 67 个个体的质体基因座和 1077 个双酶切限制性位点相关 DNA (ddRAD) 基因座进行了测序。使用 STRUCTURE 将基因型分配给分类群内和分类群之间的主要遗传簇测试是否 P. helvetica 代表了一个遗传分化的谱系，并解决了其杂交起源的假设。比较生态模型进一步解决了分类群之间可能的生态位差异。主要结果 P. helvetica 被强调为与共生分类群不同的遗传同质物种。与杂交物种形成的情况一致，它提供了 P. officinalis (2n = 16) 和 P. mollis sl (2n = 18, 22) 之间平衡混合的明确证据，后者也被强调为基于质体序列的母本祖先。母体祖先内有限的遗传结构与 P. helvetica 的起源一致，通过具有相当大核型变化的同倍体杂交或通过涉及 P. mollis sl 的异倍体分类群的异源多倍体的复杂情况 比较生态位模型表明 P. helvetica 及其祖先之间的生态差异不显着，支持杂交产生的内在因素是物种形成的主要驱动因素。结论 杂交似乎是促进狭窄的地方性 P. helvetica 的冰后起源的主要过程，表明杂交物种形成是在气候变化下快速产生新物种的有效过程。