A fundamental objective of evolutionary biology is to understand the origin of independently evolving species. Phylogenetic studies of species radiations rarely are able to document ongoing speciation; instead, modes of speciation, entailing geographic separation and/or ecological differentiation, are posited retrospectively. The Oreinotinus clade of Viburnum has radiated recently from north to south through the cloud forests of Mexico and Central America to the Central Andes. Our analyses support a hypothesis of incipient speciation in Oreinotinus at the southern edge of its geographic range, from central Peru to northern Argentina. Although several species and infraspecific taxa have been recognized in this area, multiple lines of evidence and analytical approaches (including analyses of phylogenetic relationships, genetic structure, leaf morphology, and climatic envelopes) favor the recognition of just a single species, V. seemenii. We show that what has previously been recognized as V. seemenii f. minor has recently occupied the drier Tucuman-Bolivian forest region from Samaipata in Bolivia to Salta in northern Argentina. Plants in these populations form a well-supported clade with a distinctive genetic signature and they have evolved smaller, narrower leaves. We interpret this as the beginning of a within-species divergence process that has elsewhere in the neotropics resulted repeatedly in Viburnum species with a particular set of leaf ecomorphs. Specifically, the southern populations are in the process of evolving the small, glabrous, and entire leaf ecomorph that has evolved in four other montane areas of endemism. As predicted based on our studies of leaf ecomorphs in Chiapas, Mexico, these southern populations experience generally drier conditions, with large diurnal temperature fluctuations. In a central portion of the range of V. seemenii, characterized by wetter climatic conditions, we also document what may be the initial differentiation of the leaf ecomorph with larger, pubescent, and toothy leaves. The emergence of these ecomorphs thus appears to be driven by adaptation to subtly different climatic conditions in separate geographic regions, as opposed to parapatric differentiation along elevational gradients as suggested by Viburnum species distributions in other parts of the neotropics.

中文翻译：

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行为捕获：安第斯山脉中部荚蒾南端的早期物种形成。


进化生物学的一个基本目标是了解独立进化物种的起源。物种辐射的系统发育研究很少能够记录正在进行的物种形成;相反，回顾性地假设了物种形成模式，包括地理分离和/或生态分化。荚蒾的 Oreinotinus 分支最近从北向南辐射，穿过墨西哥和中美洲的云雾森林，到达安第斯山脉中部。我们的分析支持了 Oreinotinus 在其地理范围的南部边缘（从秘鲁中部到阿根廷北部）形成早期物种形成的假设。尽管在该领域已经确定了几个物种和种下分类群，但多种证据和分析方法（包括对系统发育关系、遗传结构、叶形态和气候包络的分析）支持仅识别一个物种，即 V. seemenii。我们表明，以前被认为是 V. seemenii f. minor 的物种最近占据了从玻利维亚的 Samaipata 到阿根廷北部的 Salta 的干燥的图库曼-玻利维亚森林地区。这些种群中的植物形成了一个具有独特遗传特征的得到良好支持的分支，它们已经进化出更小、更窄的叶子。我们将其解释为种内分化过程的开始，该过程在新热带的其他地方反复导致荚蒾物种具有一组特定的叶生态型。具体来说，南方种群正在进化出在其他四个山地特有地区进化而来的小、无毛和全叶生态形态。 根据我们对墨西哥恰帕斯州叶生态型体的研究预测，这些南部种群通常经历较干燥的条件，昼夜温度波动较大。在 V. seemenii 范围的中心部分，以更潮湿的气候条件为特征，我们还记录了叶子生态型体的初始分化，叶子更大、有短柔毛和有齿。因此，这些生态形态的出现似乎是由对不同地理区域微妙不同的气候条件的适应驱动的，而不是像新热带其他地区的荚蒾物种分布所暗示的那样沿海拔梯度的旁系分化。