Species of new world silversides (Actinopterygii; Atherinopsidae; genus Odontesthes) possess economic relevance, biological interest and ecological importance. In the present paper we: (A) investigate the molecular diversity in marine species of Odontesthes from the South West Atlantic Ocean (SWAO), and analyse their interspecific relationships and divergence by means of DNA Barcoding, including its freshwater congeners, as well. (B) Explore the suitability of DNA Barcoding to analyse the diversity and distribution of haplotypes in Odontesthes argentinensis, the only well documented marine species from the SWAO that exhibit putative estuarine and marine populations. Molecular analysis revealed 100% of agreement between morphological identification and molecular identity. Odontesthes argentinensis, Odontesthes platensis, Odontesthes smitti, Odontesthes nigricans and Odontesthes incisa were assigned to five different barcode index numbers (BINs). Maximum-likelihood analysis showed that all marine species of Odontesthes clustered separately in a unique monophyletic phylogroup, comprising five well defined haplogroups, with genetic divergence between groups ranging from 2.75 to 7.11%. The genetic analysis including freshwater congeners showed that O. incisa clustered alone occupying a basal position. The Fst pairwise comparisons within O. argentinensis support the existence of three population groups: one conformed by Mar Chiquita Lagoon (MCh) specimens, and the others by Mar del Plata/Mar Chiquita coast and San Blas Bay coastal specimens, respectively. The AMOVA showed significant overall differentiation (Fst = 0.238; p = 0.00001) for the entire data set. The previous/present evidence is discussed, and strongly suggests that incipient speciation is occurring in O. argentinensis argentinean populations, and specimens from MCh would be considered at present as the leading candidate of a marine to freshwater incipient speciation event.

中文翻译：

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推断新世界银鱼（Atherinopsidae；属 Odontesthes）鱼类之间的界限：Odontesthes argentinensis 海洋和半咸水种群之间早期物种形成的新证据

新世界银鱼（Actinopterygii；Atherinopsidae；Odontesthes 属）的物种具有经济相关性、生物学意义和生态重要性。在本文中，我们：(A) 研究了西南大西洋 (SWAO) 的 Odontesthes 海洋物种的分子多样性，并通过 DNA 条形码分析了它们的种间关系和差异，包括其淡水同源物。(B) 探索 DNA Barcoding 在分析 Odontesthes argentinensis 中单倍型的多样性和分布的适用性，Odontesthes argentinensis 是 SWAO 中唯一有据可查的海洋物种，具有推定的河口和海洋种群。分子分析揭示了形态学鉴定和分子同一性之间 100% 的一致性。Odontesthes argentinensis, Odontesthes platensis, Odontesthes smitti, Odontesthes nigricans 和 Odontesthes incisa 被分配到五个不同的条形码索引号 (BIN)。最大似然分析表明，所有 Odontesthes 的海洋物种分别聚集在一个独特的单系系统群中，包括五个明确定义的单倍群，组间的遗传差异范围为 2.75% 到 7.11%。包括淡水同源物在内的遗传分析表明，O. incisa 单独聚集，占据基部位置。O. argentinensis 内的 Fst 成对比较支持三个种群组的存在：一个符合 Mar Chiquita Lagoon (MCh) 标本，另一个符合 Mar del Plata/Mar Chiquita 海岸和圣布拉斯湾沿海标本。AMOVA 对整个数据集显示出显着的整体差异（Fst = 0.238；p = 0.00001）。