Cytogenetic analyses of Bryconamericus aff. iheringii specimens from the upper Paraná River basin (State of Paraná, Brazil) are provided. They had 2n = 52 chromosomes and two cytotypes with variations in their karyotypic formulae: cytotype I with 12 metacentric, 18 submetacentric, 8 subtelocentric and 14 acrocentric chromosomes with a fundamental number (FN) of 90; cytotype II with 8 metacentric, 28 submetacentric, 6 subtelocentric and 10 acrocentric chromosomes with a fundamental number (FN) of 94. Differences in C- and G-band patterns between the cytotypes, distinguishing marker chromosomes for each karyotype, were reported. The R-band pattern by 5-bromodeoxyuridine incorporation was obtained in chromosomes of the cytotype II sample. In some metaphases, the second pair of submetacentric chromosomes is distinctive: its short arm is heterochromatic (positive C-band), corresponding to a late replication region. In the same cytotype, a G- and R-band size heteromorphism w as recorded in the long arm of pair 9 (submetacentric). These methodologies revealed an actual karyotypic differentiation in the B. aff. iheringii population analyzed. Morphometrical comparative analyses and a discussion of evolutionary aspects of chromosome diversification in species of this genus are provided as well.
The group Incertae sedis within the Characidae family currently includes 88 genera, previously included in the subfamily Tetragonopterinae. Among them is the genus Astyanax comprising a group of species with similar morphology and widely distributed in the Neotropics. Thus, the present study aimed to analyze the karyotype diversity in Astyanax species from different watersheds by conventional Giemsa staining, C-banding and fluorescence in situ hybridization (FISH rDNA 18S) probe.specimens of Astyanax aff. paranae belonging to the "scabripinnis complex", Astyanax asunsionensis and Astyanax aff. bimaculatus were analyzed". Two sympatric karyomorphs were observed in Astyanax. aff paranae, one of them having2n=48andthe other one with 2n=50 chromosomes. Other population of this same species also presented 2n=50 chromosomes, but differing in the karyotype formula and with macro supernumerary chromosome found in 100% of the cells in about 80%of females analyzed. Two population of A. asuncionensis and one population of Astyanax. aff. bimaculatus, also showed a diploid number of 50 chromosomes, but also differing in their karyotype formulas. Therefore, A. asuncionensis was also characterized by intraspecific chromosome diversity. The C-banding analysis was able to demonstrate a distinctable to demonstrate a distinct pattern of heterochromatin differing A. asuncionensis from Astyanax aff. paranae and Astyanax aff. bimaculatus. The supernumerary chromosome of Astyanax aff. paranae proved completely heterochromatic. Only Astyanax.aff. bimaculatus multiple showed multiple sites of nucleolar organizing regions. The other species were characterized by having a simple system of NOR. These data contributes to the know ledge of the existing biodiversity in our fish fauna, here highlighted by the inter-and intraspecific chromosomal diversity in the genus Astyanax.Keywords: cytogenetics, biodiversity, B chromosomes, C-bands, NORs. Diversidade Cariotípica entre três espécies do gênero
The Astyanax scabripinis population from the São Francisco River, analyzed in the present study, had two different diploid numbers: 2n=50 chromosomes (cytotype I) with the karyotypic formula of 10m+20sm+8st+12a and NF=88, and 2n=48 chromosomes (cytotype II) with the karyotypic formula of 11m +18sm+9st+10a and NF=86. Individuals with cytotype II also had a heteromorphic pair in male and female karyotype (24 pair), and in some cells, a supernumerary acrocentric chromosome, which was similar in size to the last acrocentric. C-banding and Ag-NOR staining patterns also differed between the two cytotypes, reinforcing the hypothesis that there are two different species and that A. scabripinnis is a species complex.
<p>A família Characidade representa a maior e mais diversificada família de peixes de água doce, na qual se encontram muitos gêneros de pequeno porte. Neste estudo foram analisados, cromossomicamente, exemplares de <em>Hyphessobrycon vinaceus</em>, <em>Bryconamericus </em>aff. <em>iheringii</em> e <em>Odontostilbe pequira. H. vinaceus</em> apresentou 2n=50, sendo 8m, 12sm e 30a, com evidente proporção de ST/A, AgNOR-múltipla e blocos de heterocromatina na porção intersticial. <em>B. </em>aff. <em>iheringii</em> apresentou 2n=52, com 12m, 18sm, 8st e 14a, AgNOR-simples e blocos de heterocromatina pericentroméricos. <em>O. pequira</em> apresentou 2n= 52, sendo 14m, 20sm, 14st e 4a, com determinação cromossômica sexual do tipo ZZ/ZW e sistema de AgNOR-simples, além de blocos de heterocromatina na posição pericentromérica. A diversidade cariotípica, encontrada em peixes de pequeno porte, tem sido explicada através de mecanismos de rearranjos cromossômicos e que, provavelmente, tenham se fixado devido às características biológicas dessas espécies, que ocupam, preferencialmente, cabeceiras de rios e riachos, formando pequenas populações.</p>
<p>A família Characidade representa a maior e mais diversificada família de peixes de água doce, na qual se encontram muitos gêneros de pequeno porte. Neste estudo foram analisados, cromossomicamente, exemplares de <em>Hyphessobrycon vinaceus</em>, <em>Bryconamericus </em>aff. <em>iheringii</em> e <em>Odontostilbe pequira. H. vinaceus</em> apresentou 2n=50, sendo 8m, 12sm e 30a, com evidente proporção de ST/A, AgNOR-múltipla e blocos de heterocromatina na porção intersticial. <em>B. </em>aff. <em>iheringii</em> apresentou 2n=52, com 12m, 18sm, 8st e 14a, AgNOR-simples e blocos de heterocromatina pericentroméricos. <em>O. pequira</em> apresentou 2n= 52, sendo 14m, 20sm, 14st e 4a, com determinação cromossômica sexual do tipo ZZ/ZW e sistema de AgNOR-simples, além de blocos de heterocromatina na posição pericentromérica. A diversidade cariotípica, encontrada em peixes de pequeno porte, tem sido explicada através de mecanismos de rearranjos cromossômicos e que, provavelmente, tenham se fixado devido às características biológicas dessas espécies, que ocupam, preferencialmente, cabeceiras de rios e riachos, formando pequenas populações.</p>
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