This paper presents results from a comparative analysis of cytogenetic markers, DNA barcode, molecular delimitation and population genetics among four groups of Apareiodon samples inhabiting four headwater streams feeding the Tocantins River in Brazil’s Tocantins River Basin. Apareiodon is a genus of Parodontidae, a Neotropical fish family whose members show often-subtle morphological diagnostic characters that complicate identification of its constituent species. The samples were previously morphologically identified as Apareiodon machrisi, Apareiodon cavalcante, Apareiodon sp. 1, and Apareiodon sp. 2. The cytogenetic results showed a shared diploid number of 54 chromosomes, and no heteromorphic sex chromosomes were detected. In situ localization of repetitive DNA sequences (18S and 5S ribosomal DNAs, (GATA)_n sequence, pPh2004 satellite DNA, and WAp repetitive fraction) revealed karyotype differences among the four groups of samples. The K2P genetic distance among the groups ranged from 0.79 to 4.27%. Species delimitation analyses diverge in taxa number: general mixed Yule-coalescent data suggested the occurrence of three species; and the Bayesian and neighbor-joining trees revealed four clades, three of them being supported clades (A. machrisi + Apareiodon sp. 1, A. cavalcante, and Apareiodon sp. 2). Haplotypes did not overlap and high Fst values were observed among the groups. The data suggest that these samples have had a recent parapatric divergence: A. cavalcante and A. machrisi are valid species; Apareiodon sp. 1 may be a lineage related to A. machrisi, possibly undergoing an incipient process of speciation; and Apareiodon sp. 2 may be a new Apareiodon molecular operational taxonomic unit.

本文介绍了对四类Apareiodon样本的细胞遗传学标记，DNA条形码，分子定界和种群遗传学的比较分析结果，这些样本居住在四个以巴西Tocantins流域的Tocantins河为食的上游水源。Apareiodon是新热带鱼科Parodontidae的一个属，其成员表现出通常微妙的形态学诊断特征，使其组成物种的鉴定复杂化。样品先前形态认定为Apareiodon machrisi，Apareiodon卡瓦尔坎特，Apareiodon SP。1和Apareiodonsp。2.细胞遗传学结果显示共有54条染色体的二倍体数，未检测到异型性染色体。重复DNA序列（18S和5S核糖体DNA，（GATA）_n序列，p Ph 2004卫星DNA和W Ap重复级分）的原位定位揭示了四组样品之间的核型差异。各组之间的K2P遗传距离为0.79至4.27％。物种定界分析在分类单元数上有所不同：一般的混合Yule-coalescent数据表明存在3种。贝叶斯树和邻近的树显示了四个进化枝，其中三个是支持进化枝（A. machrisi  +  Apareiodon sp。1，A. cavalcante和Apareiodon sp。2）。单倍型不重叠，并且在各组之间观察到高的Fst值。数据表明，这些样本最近出现了同族异种差异：A. cavalcante和A. machrisi是有效物种；Apareiodon sp。1可能是与A. machrisi有关的血统，可能经历了初期的物种形成过程；和Apareiodon sp。2可能是新的Apareiodon分子操作分类单位。