Genetic and Chromosomal Differentiation of Rhamdia quelen (Siluriformes, Heptapteridae) Revealed by Repetitive Molecular Markers and DNA Barcoding.

Rhamdia quelen, a species of Heptapteridae, is considered to be a complex because of taxonomic and phylogenetic inconsistencies. Determining the physical location of repetitive DNA sequences on the chromosomes and the DNA barcode might increase our understanding of these inconsistencies within different groups of fish. To this end, we analyzed R. quelen populations from two river basins in Brazil, Paraguay and Parana, using DNA barcoding and different chromosomal markers, including U2 snDNA, which has never been analyzed for any Rhamdia species. Cytochrome c oxidase I gene sequence analysis revealed a significant differentiation among populations from the Miranda and Quexada rivers, with genetic distances compatible to those found among different species in neotropical fishes. Our results, in general, revealed a conservative chromosomal evolution in R. quelen and a differential distribution of some markers, such as 5S rDNA and U2 snDNA, in different populations. We suggest that R. quelen must undergo a major revision in its morphological, genetic, and cytogenetic molecular and taxonomic structure to elucidate possible operational taxonomic units.

Chromosomal Mapping of Repetitive DNA Sequences in the Genus Bryconamericus (Characidae) and DNA Barcoding to Differentiate Populations.

The mapping of repetitive DNA sites by fluorescence in situ hybridization has been widely used for karyotype studies in different species of fish, especially when dealing with related species or even genera presenting high chromosome variability. This study analyzed three populations of Bryconamericus, with diploid number preserved, but with different karyotype formulae. Bryconamericus ecai, from the Forquetinha river/RS, presented three new cytotypes, increasing the number of karyotype forms to seven in this population. Other two populations of Bryconamericus sp. from the Vermelho stream/PR and Cambuta river/PR exhibited interpopulation variation. The chromosome mapping of rDNA sites revealed unique markings among the three populations, showing inter- and intrapopulation variability located in the terminal region. The molecular analysis using DNA barcoding complementing the cytogenetic analysis also showed differentiation among the three populations. The U2 small nuclear DNA repetitive sequence exhibited conserved features, being located in the interstitial region of a single chromosome pair. This is the first report on its occurrence in the genus Bryconamericus. Data obtained revealed a karyotype variability already assigned to the genus, along with polymorphism of ribosomal sites, demonstrating that this group of fish can be undergoing a divergent evolutionary process, constituting a substantive model for studies of chromosomal evolution.