The riverine barrier hypothesis proposes that large rivers represent geographical barriers to gene flow for terrestrial organisms, leading to population differentiation and ultimately allopatric speciation. Here we assess for the first time if the subtropical Paraná–Paraguay River system in the Del Plata basin, second in size among South American drainages, acts as a barrier to gene flow for birds. We analysed the degree of mitochondrial and nuclear genomic differentiation in seven species with known subspecies divided by the Paraná–Paraguay River axis. Only one species showed genetic differentiation concordant with the current river channel, but another five species have an east/west genetic split broadly coincident with the Paraná River's dynamic palaeochannel, suggesting this fluvial axis has had a past role in shaping present‐day genetic structure. Moreover, dating analyses show that these splits have been asynchronous, with species responding differently to the riverine barrier. Comparisons informed by the geological history of the Paraná River and its influence on the ecological and climatic differences among ecoregions in the study area further bolster the finding that responses to this geographical barrier have been species‐specific.

中文翻译：

---

对新热带地区最大的亚热带流域的河流障碍假设进行检验。

河流屏障假说提出，大河流代表了陆地生物基因流动的地理屏障，从而导致了种群分化和最终的异源物种形成。在这里，我们首次评估了Del Plata盆地中亚热带的Paraná-Paraguay河系是否对鸟类的基因流动产生了障碍，该系统在南美排水系统中仅次于第二。我们分析了七个已知亚种的种的线粒体分化程度和核基因组分化程度，这些亚种被巴拉那–巴拉圭河轴线划分。只有一种物种的遗传分化与当前河道相符，但是另外五种物种的东西向遗传分裂与巴拉那河的动态古河道大致相符，提示这个河流轴在塑造当今的遗传结构中起着过去的作用。此外，定年分析表明这些分裂是异步的，物种对河流屏障的反应不同。根据巴拉那河的地质历史进行的比较及其对研究区域生态区域之间生态和气候差异的影响，进一步支持了这一对地理障碍的反应是特定物种的发现。