Karyotype Evolution of Talking Thorny Catfishes <b><i>Anadoras</i></b> (Doradidae, Astrodoradinae): A Process Mediated by Structural Rearrangements and Intense Reorganization of Repetitive DNAs

Abstract

<i>Anadoras</i> is a thorny catfish genus widespread through the Amazon and Paraguay river basins. It includes 2 nominal species, <i>A. grypus</i> and <i>A. weddellii</i>, plus <i>Anadoras</i> sp. “araguaia,” an undescribed species only recognized morphologically. Since <i>Anadoras</i> occupies a basal position within the Astrodoradinae phylogeny, it is crucial to identify its cytogenetic features to comprehend the mechanisms involved in the chromosomal diversification of this subfamily. Therefore, we performed a comparative cytogenetic analysis including all species of <i>Anadoras</i>. Furthermore, we applied a species delimitation analysis based on 600 bp of the mitochondrial cytochrome oxidase subunit 1 (<i>CO1</i>) gene to investigate the taxonomic status of the species. Cytogenetic markers revealed a high degree of similarity among <i>Anadoras weddellii</i> and <i>Anadoras</i> sp. “araguaia,” both have 2n = 56 chromosomes (24m + 10sm + 22st/a), single NOR sites on acrocentric pair 28, and 5S rDNA sites on submetacentric pair 15. <i>A. grypus</i> has the most divergent chromosomal characteristics because, even though it also has 2n = 56 chromosomes, it exhibits several differences in the chromosome formula, heterochromatin distribution, and number/position of the rDNA sites. In sum, we believe that the chromosome diversification of <i>Anadoras</i> is due to 4 mechanisms: centric fusion, pericentric/paracentric inversions, nonreciprocal translocations, and activity of transposable elements. Additionally, our phylogenetic tree revealed well-supported clades and, by barcode species delimitation analysis, confirmed the existence of 3 molecular operational taxonomic units, including the putative new species <i>Anadoras</i> sp. “araguaia.”