Data from: Wide but not impermeable: Testing the riverine barrier hypothesis for an Amazonian plant species

Wallace's riverine barrier hypothesis postulates that large rivers, such as the Amazon and its tributaries, reduce or prevent gene flow between populations on opposite banks, leading to allopatry and areas of species endemism occupying interfluvial regions. Several studies have shown that two major tributaries, Rio Branco and Rio Negro, are important barriers to gene flow for birds, amphibians and primates. No botanical studies have considered the potential role of the Rio Branco as a barrier, while a single botanical study has evaluated the Rio Negro as a barrier. We studied an Amazon shrub, Amphirrhox longifolia (A. St.-Hil.) Spreng (Violaceae), as a model to test the riverine barrier hypothesis. Twenty-six populations of A. longifolia were sampled on both banks of the Rio Branco and Rio Negro in the core Amazon basin. Double digest RADseq was used to identify 8,010 unlinked SNP markers from the nuclear genome of 156 individuals. Data relating to population structure support the hypothesis that the Rio Negro acted as a significant genetic barrier for A. longifolia. On the other hand, no genetic differentiation was detected among populations spanning the narrower Rio Branco, which is a tributary of the Rio Negro. This study shows that the strength of riverine barriers for Amazon plants is dependent on the width of the river separating populations and species-specific dispersal traits. Future studies of plants with contrasting life history traits will further improve our understanding of the landscape genetics and allopatric speciation history of Amazon plant diversity.

华莱士河岸屏障假说（Wallace's riverine barrier hypothesis）提出，大型河流（如亚马逊河及其支流）会削弱甚至阻断两岸种群间的基因交流，进而形成异域分布格局，且河间区域会形成特有物种分布区。已有多项研究表明，两大支流布兰科河（Rio Branco）与内格罗河（Rio Negro）是鸟类、两栖类与灵长类动物基因交流的重要屏障。目前尚无植物学研究探讨布兰科河的屏障效应，仅1项植物学研究对内格罗河的屏障作用进行了评估。本研究以亚马逊灌木长叶两栖花（Amphirrhox longifolia (A. St.-Hil.) Spreng，堇菜科（Violaceae））为模型物种，以验证河岸屏障假说。研究人员在亚马逊盆地核心区域的布兰科河与内格罗河两岸，共采集了26个长叶两栖花种群样本。通过双酶切限制性位点关联DNA测序（Double digest RADseq）技术，从156个个体的核基因组中鉴定出8010个非连锁单核苷酸多态性（Single Nucleotide Polymorphism, SNP）标记。种群结构相关数据分析结果支持"内格罗河是长叶两栖花的重要遗传屏障"这一假说。另一方面，作为内格罗河支流的较窄布兰科河两岸的种群之间，未检测到遗传分化。本研究表明，亚马逊植物所受河岸屏障的强度，取决于分隔种群的河流宽度以及物种特有的扩散性状。未来针对具有迥异生活史特征的植物开展相关研究，将进一步深化我们对亚马逊植物多样性的景观遗传学以及异域物种形成历史的认知。