First report of B chromosomes in three neotropical thorny catfishes (Siluriformes, Doradidae)

Abstract

The family Doradidae (Siluriformes) is an important group of fishes endemic to freshwater ecosystems in South America. Some cytogenetic studies have been conducted focused on the group; however, there are no reports on the occurrence of B chromosomes for the family. In this paper the chromosomal characteristics of Platydoras armatulus (Valenciennes, 1840), Pterodoras granulosus (Valenciennes, 1821) and Ossancora punctata (Kner, 1855) were investigated through classical cytogenetics approaches. The conventional staining reveals 2n=58 in Platydoras armatulus and Pterodoras granulosus, however with distinct karyotypic formulae, possibly originated by pericentric inversions. In Ossancora punctata a derivate karyotype was described with 2n=66 and predominance of acrocentric chromosomes. The C banding pattern was resolutive in discriminating the three species, being considered an important cytotaxonomic marker. All species showed B chromosomes totally heterochromatic with non-Mendelian segregation during meiosis and low frequencies in mitotic cells. The probably origin of these additional elements was through fragmentations of chromosomes of the standard complement, which occurred recently and independently in these three species. The diploid number observed in Ossancora punctata is an evidence of centric fusions and up to the moment it is the highest diploid number reported for Doradidae.

A New Variant B Chromosome in Auchenipteridae: The Role of (GATA)_n and (TTAGGG)_n Sequences in Understanding the Evolution of Supernumeraries in <b><i>Trachelyopterus</i></b>

“…1e, g). Commonly, Bs are structurally different from complement A chromosomes; they can range from small dots in the normal karyotype [Takagui et al, 2017] to larger chromosomes [de A . Despite the great variability, in fish, B chromosomes smaller than the smallest complement A chromosome are the most commonly described morphology [Jones and Rees, 1982].…”

“…The (GATA) n repeats were found spread throughout the genome, but in contrast to the complement A chromosomes, both B1 of T. galeatus and B1 and B2 of T. porosus had clustered blocks. Bs are often products of genome evolution processes resulting from a fragmented A chromosome [Camacho et al, 2000;Navarro-Domínguez et al, 2017;Takagui et al, 2017;Valente et al, 2017]. After fragmentation, an intragenomic race immediately starts to decide whether this new fragment will remain.…”

“…In most organisms, Bs are nonessential [Huang et al, 2016;Hanlon et al, 2018] and have no phenotypic effect [Takagui et al, 2017]. However, with the advancement of cytogenetic and molecular techniques, phenotypic and regulatory effects of Bs have been reported for some species [Banaei-Moghaddam et al, 2013].…”

Vertebrate Genome Evolution in the Light of Fish Cytogenomics and rDNAomics

“…B chromosomes are known to contain rDNA frequently e.g., [ 147 ], summarized by [ 79 , 139 ]. B chromosomes have been identified e.g., in seven South American and in fourteen African cichlid species [ 143 ], in the genus Poecilia as we already mentioned by [ 148 ], in the bleak ( Alburnus alburnus, Cyprinidae) [ 149 ] and in three species of thorny catfishes [ 150 ]. The complete list of B chromosomes identified in fishes is available in a specialized database ‘B chrom’ [ 151 ] by [ 152 ].…”