High congruence of karyotypic and molecular data on Hypostomus species from Brazilian southeast

The Hypostomini tribe comprises a single genus, Hypostomus, which possibly contains several monophyletic groups because of significant morphological variation and a variety of diploid numbers and karyotype formulas. The objective of this study was to infer evolutionary relationships among 21 species of Hypostomus found in Brazilian southeast and subsequently to identify chromosomal synapomorphies in the groupings formed. Two nuclear genes, rag1 and rag2, and two mitochondrial genes, mt-co1 and mt-cyb, were used to establish evolutionary relationships. Phylogenetic trees were inferred using the maximum likelihood (ML) method for mt-co1 and Bayesian analysis (BA) for all genes concatenated. Both phylogenetic trees showed two large monophyletic clades within Hypostomus. These clades are based on chromosome number, where haplogroup I contains individuals with 66–68 chromosomes and haplogroup II contains species with 72–80 chromosomes. A third monophyletic haplogroup was also observed using ML, formed by H. faveolus and H. cochliodon, which present 2n = 64, reinforcing the separation of groups in Hypostomus by diploid number. Robertsonian rearrangements were responsible for forming the different diploid numbers and for the diversity of karyotype formulas. Ag-NORs are predominantly multiple and located on st/a chromosomes, along with 18S rDNA sites; 5S rDNA sites are often seen in an interstitial position, following the trend already described for vertebrates. The groups based on traditional morphological taxonomy are considered artificial in this study; proposed colored patterns recognizing two large groups are supported by little chromosomal evidence, and it was considered based on homoplastic characters.