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.

B or supernumerary chromosomes are dispensable elements that are widely present in numerous eukaryotes. Due to their non-recombining nature, there is an evident tendency for repetitive DNA accumulation in these elements. Thus, satellite DNA plays an important role in the evolution and diversification of B chromosomes and can provide clues regarding their origin. The characiform Prochilodus lineatus was one of the first discovered fish species bearing B chromosomes, with all populations analyzed so far showing one to nine micro-B chromosomes and exhibiting at least three morphological variants (Ba, Bsm, and Bm). To date, a single satellite DNA is known to be located on the B chromosomes of this species, but no information regarding the differentiation of the proposed B-types is available. Here, we characterized the satellitome of P. lineatus and mapped 35 satellite DNAs against the chromosomes of P. lineatus, of which six were equally located on all B-types and this indicates a similar genomic content. In addition, we describe, for the first time, an entire population without B chromosomes.

Vanellus (Charadriidae; Charadriiformes) comprises around 20 species commonly referred to as lapwings. In this study, by integrating cytogenetic and genomic approaches, we assessed the satellite DNA (satDNA) composition of one typical species, Vanellus chilensis, with a highly conserved karyotype. We additionally underlined its role in the evolution, structure, and differentiation process of the present ZW sex chromosome system. Seven distinct satellite DNA families were identified within its genome, accumulating on the centromeres, microchromosomes, and the W chromosome. However, these identified satellite DNA families were not found in two other Charadriiformes members, namely Jacana jacana and Calidris canutus. The hybridization of microsatellite sequences revealed the presence of a few repetitive sequences in V. chilensis, with only two out of sixteen displaying positive hybridization signals. Overall, our results contribute to understanding the genomic organization and satDNA evolution in Charadriiform birds.

Chromosomal rearrangements play a significant role in the evolution of fish genomes, being important forces in the rise of multiple sex chromosomes and in speciation events. Repetitive DNAs constitute a major component of the genome and are frequently found in heterochromatic regions, where satellite DNA sequences (satDNAs) usually represent their main components. In this work, we investigated the association of satDNAs with chromosome-shuffling events, as well as their potential relevance in both sex and karyotype evolution, using the well-known Pyrrhulina fish model. Pyrrhulina species have a conserved karyotype dominated by acrocentric chromosomes present in all examined species up to date. However, two species, namely P. marilynae and P. semifasciata, stand out for exhibiting unique traits that distinguish them from others in this group. The first shows a reduced diploid number (with 2n = 32), while the latter has a well-differentiated multiple X₁X₂Y sex chromosome system. In addition to isolating and characterizing the full collection of satDNAs (satellitomes) of both species, we also in situ mapped these sequences in the chromosomes of both species. Moreover, the satDNAs that displayed signals on the sex chromosomes of P. semifasciata were also mapped in some phylogenetically related species to estimate their potential accumulation on proto-sex chromosomes. Thus, a large collection of satDNAs for both species, with several classes being shared between them, was characterized for the first time. In addition, the possible involvement of these satellites in the karyotype evolution of P. marilynae and P. semifasciata, especially sex-chromosome formation and karyotype reduction in P. marilynae, could be shown.

Scleropages formosus (Osteoglossiformes, Teleostei) represents one of the most valued ornamental fishes, yet it is critically endangered due to overexploitation and habitat destruction. This species encompasses three major color groups that naturally occur in allopatric populations, but the evolutionary and taxonomic relationships of S. formosus color varieties remain uncertain. Here, we utilized a range of molecular cytogenetic techniques to characterize the karyotypes of five S. formosus color phenotypes, which correspond to naturally occurring variants: the red ones (Super Red); the golden ones (Golden Crossback and Highback Golden); the green ones (Asian Green and Yellow Tail Silver). Additionally, we describe the satellitome of S. formosus (Highback Golden) by applying a high-throughput sequencing technology. All color phenotypes possessed the same karyotype structure 2n = 50 (8m/sm + 42st/a) and distribution of SatDNAs, but different chromosomal locations of rDNAs, which were involved in a chromosome size polymorphism. Our results show indications of population genetic structure and microstructure differences in karyotypes of the color phenotypes. However, the findings do not clearly back up the hypothesis that there are discrete lineages or evolutionary units among the color phenotypes of S. formosus, but another case of interspecific chromosome stasis cannot be excluded.

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.