title: Comparative cytogenetics in the genus Hoplias (Characiformes, Erythrinidae) highlights contrasting karyotype evolution among congeneric species.
abstract: BACKGROUND
  The Erythrinidae fish family contains three genera, Hoplias, Erythrinus and Hoplerythrinus widely distributed in Neotropical region. Remarkably, species from this family are characterized by an extensive karyotype diversity, with 2n ranging from 39 to 54 chromosomes and the occurrence of single and/or multiple sex chromosome systems in some species. However, inside the Hoplias genus, while H. malabaricus was subject of many studies, the cytogenetics of other congeneric species remains poorly explored. In this study, we have investigated chromosomal characteristics of four Hoplias species, namely H. lacerdae, H. brasiliensis, H. intermedius and H. aimara. We used conventional staining techniques (C-banding, Ag-impregnation and CMA3 -fluorescence) as well as fluorescence in situ hybridization (FISH) with minor and major rDNA and microsatellite DNAs as probes in order to analyze the karyotype evolution within the genus.
  
  
  RESULTS
  All species showed invariably 2n = 50 chromosomes and practically identical karyotypes dominated only by meta- and submetacentric chromosomes, the absence of heteromorphic sex chromosomes, similar pattern of C-positive heterochromatin blocks and homologous Ag-NOR-bearing pairs. The cytogenetic mapping of five repetitive DNA sequences revealed some particular interspecific differences between them. However, the examined chromosomal characteristics indicate that their speciation was not associated with major changes in their karyotypes.
  
  
  CONCLUSIONS
  Such conserved karyotypes contrasts with the extensive karyotype diversity that has been observed in other Erythrinidae species, particularly in the congeneric species H. malabaricus. Nevertheless, what forces drive such particularly different modes of karyotype evolution among closely related species? Different life styles, population structure and inner chromosomal characteristics related to similar cases in other vertebrate groups can also account for the contrasting modes of karyotype evolution in Hoplias genus.
authors.affiliation: Universidade Federal de São Carlos, Departamento de Genética e Evolução, São Carlos, SP Brazil ; SEDUC-MT, Cuiabá, MT Brazil.
authors.forename: Ezequiel Aguiar
authors.initials: EA
authors.lastname: de Oliveira
authors.affiliation: Universidade Federal de São Carlos, Departamento de Genética e Evolução, São Carlos, SP Brazil.
authors.forename: Luiz Antônio Carlos
authors.initials: LA
authors.lastname: Bertollo
authors.affiliation: Universidade Federal de São Carlos, Departamento de Genética e Evolução, São Carlos, SP Brazil.
authors.forename: Cassia Fernanda
authors.initials: CF
authors.lastname: Yano
authors.affiliation: Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse 10, D-07743 Jena, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Liehr
authors.affiliation: Universidade Federal de São Carlos, Departamento de Genética e Evolução, São Carlos, SP Brazil.
authors.forename: Marcelo de Bello
authors.initials: Mde B
authors.lastname: Cioffi
keywords: Chromosome change and speciation; FISH; Fish cytogenetics; Repetitive DNA; Trahiras