Otero Ana, Vargas Pablo, Fernández-Mazuecos Mario, Jiménez-Mejías Pedro, Valcárcel Virginia, Villa-Machío Irene, Hipp Andrew L
Grainger Bioinformatics Center, Department of Science and Education, The Field Museum, Chicago, Illinois, USA.
Departamento de Biodiversidad y Conservación, Real Jardín Botánico (RJB-CSIC), Madrid, Spain.
Mol Ecol. 2022 Jun;31(11):3192-3209. doi: 10.1111/mec.16459. Epub 2022 Apr 26.
Traditional classification of speciation modes has focused on physical barriers to gene flow. Allopatric speciation with complete reproductive isolation is viewed as the most common mechanism of speciation. Parapatry and sympatry, by contrast, entail speciation in the face of ongoing gene flow, making them more difficult to detect. The genus Iberodes (Boraginaceae, NW Europe) comprises five species with contrasting morphological traits, habitats and species distributions. Based on the predominance of narrow and geographically distant endemic species, we hypothesized that geographical barriers were responsible for most speciation events in Iberodes. We undertook an integrative study including: (i) phylogenomics through restriction-site-associated DNA sequencing (RAD-seq), (ii) genetic structure analyses, (iii) demographic modelling, (iv) morphometrics, and (v) climatic niche modelling and niche overlap analysis. The results revealed a history of recurrent progenitor-derivative speciation manifested by a paraphyletic pattern of nested species differentiation. Budding speciation mediated by ecological differentiation is suggested for the coastal lineage, deriving from the inland widespread Iberodes linifolia during the Late Pliocene. Meanwhile, geographical isolation followed by niche shifts are suggested for the more recent differentiation of the coastland taxa. Our work provides a model for distinguishing speciation via ecological differentiation of peripheral, narrowly endemic I. kuzinskyanae and I. littoralis from a widespread extant ancestor, I. linifolia. Ultimately, our results illustrate a case of Pliocene speciation in the probable absence of geographical barriers and get away from the traditional cladistic perspective of speciation as producing two species from an extinct ancestor, thus reminding us that phylogenetic trees tell only part of the story.
传统的物种形成模式分类主要关注基因流动的物理障碍。具有完全生殖隔离的异域物种形成被视为最常见的物种形成机制。相比之下，邻域物种形成和同域物种形成则是在基因流动持续存在的情况下发生物种形成，这使得它们更难被检测到。伊比利亚草属（紫草科，欧洲西北部）包含五个物种，它们在形态特征、栖息地和物种分布上存在差异。基于狭窄且地理上相距遥远的特有物种占主导地位的情况，我们推测地理障碍是伊比利亚草属中大多数物种形成事件的原因。我们进行了一项综合研究，包括：（i）通过限制性位点关联DNA测序（RAD-seq）进行系统基因组学研究，（ii）遗传结构分析，（iii）种群动态建模，（iv）形态测量学，以及（v）气候生态位建模和生态位重叠分析。结果揭示了一个反复出现的祖裔物种形成历史，表现为嵌套物种分化的并系模式。对于沿海谱系，推测是在上新世晚期由内陆广泛分布的亚麻叶伊比利亚草通过生态分化介导的芽殖物种形成。同时，对于沿海地区类群的较新分化，推测是地理隔离随后生态位发生转变。我们的工作提供了一个模型，用于区分通过边缘、狭域特有物种库津斯基伊比利亚草和滨海伊比利亚草与广泛分布的现存祖先亚麻叶伊比利亚草的生态分化而形成的物种。最终，我们的结果说明了一个可能不存在地理障碍的上新世物种形成案例，并且摆脱了传统的物种形成分支系统学观点，即从一个灭绝的祖先产生两个物种，从而提醒我们系统发育树只讲述了部分故事。
