Understanding the structure of hybrid zones provides valuable insights about species boundaries and speciation, such as the evolution of barriers to gene flow and the strength of selection. In river networks, studying evolutionary processes in hybrid zones can be especially challenging, given the influence of past and current river properties along with biological species‐specific traits. Here, we suggest that a natural hybrid zone between two divergent lineages of the sexually dimorphic Neotropical fish Nematocharax venustus was probably established by secondary contact as a result of a river capture event between the Contas and Pardo river basins. This putative river capture is supported by hydrogeological evidence of elbows of capture, wind gaps and geological faults. The morphological (colour pattern) and genetic (mtDNA and RADseq) variation reveal a clinal transition between parental lineages along the main river, with predominance of F2 hybrids at the centre of the hybrid zone, absence of early generation backcrosses and different levels of hybridization in the tributaries. We highlight that different sources of information are crucial for understanding how the riverscape spatial history influences the connectivity between and within river systems and, consequently, the dynamics of gene flow between freshwater lineages/species.

中文翻译：

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河景特性有助于新热带淡水鱼杂交区的起源和结构

了解杂交区的结构提供了关于物种边界和物种形成的宝贵见解，例如基因流动障碍的进化和选择的强度。在河流网络中，考虑到过去和现在的河流特性以及生物物种特异性特征的影响，研究混合区的进化过程尤其具有挑战性。在这里，我们认为，由于 Contas 和 Pardo 河流域之间的河流捕获事件，可能通过二次接触建立了两性异形的新热带鱼 Nematocharax venustus 的两个不同谱系之间的自然杂交区。这种假定的河流捕获得到了捕获弯头、风隙和地质断层的水文地质证据的支持。形态（颜色模式）和遗传（mtDNA 和 RADseq）变异揭示了沿主要河流的亲本谱系之间的临床转变，F2 杂种在杂交区的中心占优势，没有早期回交和不同水平的杂交支流。我们强调，不同的信息来源对于理解河流景观空间历史如何影响河流系统之间和内部的连通性以及因此影响淡水谱系/物种之间的基因流动动态至关重要。