Karyotype variability in six Amazonian species of the family Curimatidae (Characiformes) revealed by repetitive sequence mapping

Abstract Fishes of the Curimatidae family represent one of the most important freshwater ichthyofauna groups of Central and South America, with 117 recognized species distributed in eight genera. In this study, six species - Curimata inornata, Curimatella dorsalis, and Psectrogaster falcata collected from the Lower Araguaia River, Pará, Brazil; Curimata vittata, Curimatella meyeri, and Psectrogaster rutiloides collected from the Catalão Lake, Amazonas, Brazil - were cytogenetically analyzed, investigate the occurrence and distribution of repetitive DNA classes in the karyotypes. All species had 2n=54 metacentric/submetacentric chromosomes. Despite the conservative diploid number, we observed variations in the karyotypic structure among species. Ribosomal DNA (rDNA) 18S and 5S were found in single or multiple sites, with the first report of synteny in Curimatella dorsalis, and the occurrence of several interstitial telomeric sequences (ITSs) in species of the genera Curimatella and Psectrogaster. Interspecific karyotypic diversity both concerning structure and location/position of the nucleolar organizer regions (NOR) and ribosomal DNA, suggesting the occurrence of several non-Robertsonian rearrangements driving the evolution of this family.

摘要 脂鲤科（Curimatidae）鱼类是中南美洲最重要的淡水鱼类区系类群之一，目前已记录117个有效物种，隶属于8个属。本研究对6个物种开展细胞遗传学分析：包括采自巴西帕拉州下阿拉瓜亚河的裸身无齿脂鲤（Curimata inornata）、背斑小无齿脂鲤（Curimatella dorsalis）及镰形拟无齿脂鲤（Psectrogaster falcata），以及采自巴西亚马孙州卡塔朗湖的带纹无齿脂鲤（Curimata vittata）、迈耶小无齿脂鲤（Curimatella meyeri）与似鲷拟无齿脂鲤（Psectrogaster rutiloides），旨在探究重复DNA类群在核型中的存在与分布特征。所有物种的染色体二倍体数均为2n=54，且全部为中部着丝粒/亚中部着丝粒染色体。尽管二倍体数目较为保守，但各物种间的核型结构存在显著差异。核糖体DNA（rDNA）18S与5S位点呈现单一位点或多位点分布模式；其中背斑小无齿脂鲤（Curimatella dorsalis）中首次报道了rDNA的同线性现象，而小无齿脂鲤属（Curimatella）与拟无齿脂鲤属（Psectrogaster）的物种中均存在多个端粒中间序列（interstitial telomeric sequences, ITSs）。各物种间在核型结构、核仁组织区（nucleolar organizer regions, NOR）及核糖体DNA的位置上均存在核型多样性，这表明多套非罗伯逊重排驱动了该科鱼类的演化。