Background Studies with integrative approaches (based on different lines of evidence) are fundamental for understanding the diversity of organisms. Different data sources can improve the understanding of the taxonomy and evolution of snakes. We used this integrative approach to verify the taxonomic status of Hydrodynastes gigas (Duméril, Bibron & Duméril, 1854), given its wide distribution throughout South America, including the validity of the recently described Hydrodynastes melanogigas Franco, Fernandes & Bentim, 2007. Methods We performed a phylogenetic analysis of Bayesian Inference with mtDNA 16S and Cytb, and nuDNA Cmos and NT3 concatenated (1,902 bp). In addition, we performed traditional morphometric analyses, meristic, hemipenis morphology and coloration pattern of H. gigas and H. melanogigas. Results According to molecular and morphological characters, H. gigas is widely distributed throughout South America. We found no evidence to support that H. gigas and H. melanogigas species are distinct lineages, therefore, H. melanogigas is a junior synonym of H. gigas. Thus, the melanic pattern of H. melanogigas is the result of a polymorphism of H. gigas. Melanic populations of H. gigas can be found in the Tocantins-Araguaia basin.

中文翻译：

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Hydrodynastes gigas (Serpentes, Dipsadidae) 的形态学和分子研究，这是一种来自南美洲的广泛物种

背景研究采用综合方法（基于不同的证据）是理解生物多样性的基础。不同的数据源可以提高对蛇的分类和进化的理解。我们使用这种综合方法来验证 Hydrodynastes gigas (Duméril, Bibron & Duméril, 1854) 的分类地位，因为它在整个南美洲广泛分布，包括最近描述的 Hydrodynastes melanogigas Franco, Fernandes & Bentim, 2007 的有效性。使用 mtDNA 16S 和 Cytb 以及连接的 nuDNA Cmos 和 NT3 (1,902 bp) 对贝叶斯推理进行了系统发育分析。此外，我们对 H. gigas 和 H. melanogigas 进行了传统的形态计量分析、分枝、半阴茎形态和着色模式。结果根据分子和形态特征，H. gigas广泛分布于南美洲。我们发现没有证据支持 H. gigas 和 H. melanogigas 物种是不同的谱系，因此，H. melanogigas 是 H. gigas 的初级同义词。因此，H. melanogigas 的黑色模式是 H. gigas 多态性的结果。在 Tocantins-Araguaia 盆地可以发现黑色的 H. gigas 种群。