Análises genéticas no complexo de espécies Knodus chapadae Fowler, 1906 e Knodus breviceps Eigenmann, 1908 (CHARACIDAE : STEVARDIINAE)

Abstract

The genus Knodus Eigenmann (1911) is currently represented by 27 species among which K. chapadae and K. breviceps have morphological similarities, causing doubts about the correct biological classification and taxonomic status of these species, leading to the proposition of a synonymy where K. breviceps, should be considered junior synonym of K. chapadae, it was necessary to analyze these species at cytogenetic and molecular levels, to verify if they would in fact be a single taxonomic entity or not. Based on this taxonomic uncertainty, this work had the following objectives: (I) to test, using the methodology of DNA barcode and cytogenetic data, the hypothesis that the species in question form a single taxonomic entity; and (II) verify the genetic structuring of these species or populations. Molecular analyzes, using the COI gene, evidenced the existence of four taxonomic entities within this complex of species, where there are, for each basin sampled in this study, Paraguay and Araguaia-Tocantins Basin, two distinct taxonomic entities. Genetic distance and species delimitation analyzes (GMYC) showed a minimum barcode gap of 8.9% between the OTUs of the Upper Paraguay Basin and the OTUs of the Araguaia - Tocantins basin. The cytogenetic analyzes revealed differences between the four taxonomic entities, where differences were presented not only in the diploid number and karyotype formula, but also in the location of the nucleolar organizing regions, constitutive heterochromatin. In the Araguaia - Tocantins basin, a diploid number of 2n = 54 chromosomes was found for all analyzed populations, while for the Upper Paraguay basin 2n = 52 chromosomes were found. The karyotypic formulas also showed differences, not only between the basins, but also between the populations. The data presented here point to the existence of four species in the Knodus complex, besides evidencing that these evolved in isolation due to hydrographic barriers that prevented the gene flow among these populations. Based on these new data, the morphological analyzes of these species should be deepened to verify possible morphological differences, which will confirm the existence of two more species as well as the revalidation of K. breviceps and description of these two other species.