Cytogenetic Characterization in Two Populations of Hypostomus nigromaculatus (Loricariidae) from Upper Paraná River Basin

The extensive number of Hypostomus species necessitates further research into the cytogenetics of this group. This study conducted a crucial comparative cytogenetic analysis in two populations of H. nigromaculatus with the aim of identifying potential interpopulation chromosomal markers and contributing significantly to our understanding of the evolutionary trends of this species. Both populations of H. nigromaculatus exhibited a consistent diploid chromosome number of 2n = 76, along with distinct karyotypes and fundamental number values. A single 5S ribosomal DNA site and multiple nucleolus organizer regions sites were detected. Additionally, the presence of heterochromatin in chromosomes carrying nucleolus organizer regions was reported, except for individuals of H. nigromaculatus from the Bom Jesus Stream. Pericentric inversions (or other types of centromeric shift) and/or deletions were found to be essential in the karyotype evolution and differentiation among H. nigromaculatus. These findings are valuable for enhancing our understanding of karyotypic evolution in Hypostomus.