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Satellite DNAs (satDNAs) are tandemly repeated sequences that are usually located on the heterochromatin, and the entire collection of satDNAs within a genome is called satellitome. Primarily, these sequences are not under selective pressure and evolve by concerted evolution, resulting in elevated rates of divergence between the satDNA profiles of reproductive isolated species/populations. Here, we characterized two additional satellitomes of Characiformes fish (Colossoma macropomum and Piaractus mesopotamicus) that diverged approximately 30 million years ago, while still retaining conserved karyotype features. The results we obtained indicated that several satDNAs (50% of satellite sequences in P. mesopotamicus and 43% in C. macropomum) show levels of conservation between the analyzed species, in the nucleotide and chromosomal levels. We propose that long-life cycles and few genomic changes could slow down rates of satDNA differentiation. [ABSTRACT FROM AUTHOR]

Satellite DNA (satDNA) sequences are dynamic components of the eukaryotic genome that can play significant roles in species diversification. The Prochilodontidae family, which includes 21 Neotropical fish species, is characterized by a conserved karyotype of 2 n  = 54 biarmed chromosomes, with variation in some species and populations regarding the presence or absence of B chromosomes. This study aimed to investigate whether the chromosomal distribution of specific satDNA sequences is conserved among three Prochilodus species ( Prochilodus lineatus, Prochilodus costatus , and Prochilodus argenteus ) regarding organization and number of loci , and to compare their genomes using comparative genomic hybridization (CGH). Our results demonstrated that most satDNA sequences share a similar distribution pattern across the three species, and CGH analysis corroborated that their karyotypes are very similar in terms of repetitive DNA distribution. We also identified a potential CENP-B box sequence within PliSat01, a satDNA located in the pericentromeric region of all analyzed species. In contrast, PliSat04 and PliSat14 displayed differential locations and variations in the number of loci per genome, underscoring the dynamic nature of repetitive sequences even in species with otherwise highly conserved genomes. These findings represent the first evidence of karyotype diversification in Prochilodus , highlighting the evolutionary dynamism of satDNA sequences., Competing Interests: The authors declare there are no competing interests.

The underlying processes behind the formation, evolution, and long-term maintenance of multiple sex chromosomes have been largely neglected. Among vertebrates, fishes represent the group with the highest diversity of multiple sex chromosome systems and, with six instances, the Neotropical fish genus Harttia stands out by presenting the most remarkable diversity. However, although the origin mechanism of their sex chromosome systems is well discussed, little is known about the importance of some repetitive DNA classes in the differentiation of multiple systems. In this work, by employing a combination of cytogenetic and genomic procedures, we evaluated the satellite DNA composition of H. carvalhoi with a focus on their role in the evolution, structure, and differentiation process of the rare XY1Y2 multiple-sex chromosome system. The genome of H. carvalhoi contains a total of 28 satellite DNA families, with the A + T content ranging between 38.1% and 68.1% and the predominant presence of long satellites. The in situ hybridization experiments detected 15 satellite DNAs with positive hybridization signals mainly on centromeric and pericentromeric regions of almost all chromosomes or clustered on a few pairs. Five of them presented clusters on X, Y1, and/or Y2 sex chromosomes which were therefore selected for comparative hybridization in the other three congeneric species. We found several conserved satellites accumulated on sex chromosomes and also in regions that were involved in chromosomal rearrangements. Our results provide a new contribution of satellitome studies in multiple sex chromosome systems in fishes and represent the first satellitome study for a Siluriformes species., (© The Author(s) 2024. Published by Oxford University Press on behalf of The American Genetic Association. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Complete mitochondrial genomes of the characiform fishes Astyanax fasciatus , Astyanax altiparanae , Hoplias malabaricus (Karyomorph A) and the Gymnotiformes species Gymnotus sylvius and Gymnotus cuia were characterized in the present study. The whole mitogenomes varied from 16,400bp ( A. fasciatus) to 17,730 bp ( A. altiparanae ) long and all of them consisted of 13 protein-coding genes, 22 tRNAs, 2 rRNAs genes, a control region, and origin of light-strand replication. The gene order was similar among all the analyzed species. The nucleotide content of all mitogenomes was also similar, with 29.58-30.95% for A, 27.02-28.65% for T, 26.29-29.99% for C, and 14.41-15.67% for G., Competing Interests: No potential conflict of interest was reported by the authors., (© 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)