Abstract：
The Doradidae fishes constitute one of the most diverse groups of Neotropical freshwater environments. Acanthodoradinae is the oldest lineage and the sister group to all other thorny catfishes, and it includes only the genus Acanthodoras. The diversity of Acanthodoras remains underestimated, and the use of complementary approaches, including genetic studies, is an important step to better characterize this diversity and the relationships among the species within the genus. Therefore, we conducted a comprehensive analysis using conventional cytogenetic techniques and physical mapping of three multigene families (18S and 5S ribosomal DNA [rDNA], U2 small nuclear DNA [snDNA]) and four microsatellite motifs, namely (AC)n, (AT)n, (GA)n, and (GATA)n, in two sympatric species from the Negro River: Acanthodoras cataphractus and Acanthodoras cf. polygrammus. We found significant differences in constitutive heterochromatin (CH) content, distribution of the microsatellite (AT)n, and the number of 5S rDNA and U2 snDNA sites. These differences may result from chromosome rearrangements and repetitive DNA dispersal mechanisms. Furthermore, the characterization of the diploid number (2n) of these Acanthodoras species enables us to propose 2n = 58 chromosomes as the plesiomorphic 2n state in Doradidae based on ancestral state reconstruction. Acanthodoradinae is the oldest lineage of the thorny catfishes, and knowledge about its cytogenetic patterns is crucial for disentangling the karyotype evolution of the whole group. Thus, this study contributes to the understanding of the mechanisms behind chromosome diversification of Doradidae and highlights the importance of Acanthodoradinae in the evolutionary history of thorny catfishes.
摘要：
Doradidae鱼类构成了新热带淡水环境中最多样化的群体之一。刺五加科是最古老的谱系，也是所有其他棘手cat鱼的姐妹群体，它只包括棘皮属。Acanthodoras的多样性仍然被低估，以及使用互补的方法，包括基因研究,是更好地表征这种多样性和属内物种之间关系的重要步骤。因此,我们使用常规的细胞遗传学技术和三个多基因家族（18S和5S核糖体DNA[rDNA]，U2小核DNA[snDNA])和四个微卫星基序，即(AC)n，(AT)n,(GA)n,和(GATA)n，在内格罗河的两个同胞物种中：Acanthodorascataphractus和Acanthodorascf。polygrammus.我们发现组成性异染色质（CH）含量存在显着差异，微卫星(AT)n的分布，5SrDNA和U2snDNA位点的数量。这些差异可能是由染色体重排和重复DNA分散机制引起的。此外，这些Acanthodoras物种的二倍体数（2n）的表征使我们能够根据祖先状态重建，提出2n=58条染色体作为Doradidae中的多态2n状态。刺五加科是棘手的鲶鱼中最古老的谱系，了解其细胞遗传学模式对于解开整个群体的核型进化至关重要。因此，这项研究有助于了解Doradidae染色体多样化背后的机制，并强调了Acanthodoradinae在棘手cat鱼进化史中的重要性。
