Comparative Cytogenetics and Molecular Phylogeography in the Group Astyanax altiparanae - Astyanax aff. bimaculatus (Teleostei, Characidae)

The genus Astyanax comprises small characin fish of the neotropical region. The so-called `yellow-tailed characins` compose one of the most widely distributed Astyanax groups. A. altiparanae and A. aff. bimaculatus, are evolutionarily closely related and commonly found in several Brazilian hydrographic basins. In the present work, chromosomal data of specimens of A. altiparanae and A. aff. bimaculatus from 4 hydrographic basins in the states of Sao Paulo (Upper Tiete, Paranapanema, Ribeira de Iguape) and Rio de Janeiro (Guapimirim) are shown. All the populations showed 50 chromosomes, with different karyotypic formula. Although only a single Ag-NOR bearing chromosome pair was observed, all populations possess multiple cistrons of 18S rDNA. FISH with the 5S rDNA probe showed single signals at the interstitial position of one metacentric chromosome pair. C-bands are distributed in the terminal and interstitial regions of several chromosomes. However, the As-51 satDNA are frugally located in a few chromosomes of fishes from Upper Tiete, Paranapanema and Guapimirim Rivers, being absent in individuals of A. aff. bimaculatus from Ribeira de Iguape River basin. Beside these 4 populations, molecular phylogeography studies were also performed in individuals from Middle and Lower Tiete River basin and from 2 additional collection sites in the Paranapanema and Ribeira de Iguape River basins. The phylogeographic analysis using 2 mtDNA regions (totalizing 1.314 bp of ND2 and ATPase6/8 genes) of 8 populations of the group of `yellow-tailed characins` from 3 major hydrographic basins showed structuring of populations, suggesting a correlation between chromosomal (nuclear) and molecular (mitochondrial) data. Copyright (C) 2011 S. Karger AG, Basel

Astyanax bockmanni Vari and Castro, 2007: an ambiguous karyotype in the Astyanax genus

Despite the widespread distribution of Astyanax bockmanni in streams from Upper Parana River system in central, southeastern, and southern Brazil, just recently, it has been identified as a distinct Astyanax species. Cytogenetic studies were performed in two populations of this species, revealing conservative features. A. bockmanni shows 2n = 50 chromosomes, a karyotypic formula composed of 10 M + 12SM + 12ST + 16A and multiple Ag-NORs. Eight positive signals in subtelocentric/acrocentric chromosomes were identified by fluorescent in situ hybridization (FISH) with 18S rDNA probes. After FISH with 5S rDNA probes, four sites were detected, comprising the interstitial region of a metacentric pair and the terminal region on long arms of another metracentric pair. Little amounts of constitutive heterochromatin were observed, mainly distributed at distal region in two chromosomal pairs. Additionally, heterochromatin was also located close to the centromeres in some chromosomes. No positive signals were detected in the chromosomes of A. bockmanni by FISH with the As-51 satellite DNA probe. The studied species combines a set of characteristics previously identified in two different Astyanax groups. The chromosomal evolution in the genus Astyanax is discussed.

The species complex Astyanax fasciatus Cuvier (Teleostei, Characiformes) - a multidisciplinary approach

Cytogenetic data have provided important clues that the Astyanax fasciatus populations from the Upper Parana River basin could be a part of a more diverse fish group, usually included on the same taxa. Samples collected in Cachoeira de Emas, SP, in Mogi-Guacu River basin, show two major cytotypes presenting 2n = 46 and 2n = 48 chromosomes, with distinct karyotypic formula, despite the fact that the molecular data suggested some degree of gene flow between these cytotypes. Cytogenetic and morphometric analyses were performed in this species, aiming to contribute to the understanding of the natural history from such fish group. Two allopatric populations with distinct standard cytotypes were analysed, and the data obtained suggest the separation into two groups. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.

Chromosome polymorphism in Astyanax fasciatus (Teleostei, Characidae). 2-Chromosomal location of a satellite DNA

Studies about composition of repetitive sequences and their chromosomal location have been helpful to evolutionary studies in many distinct organisms. In order to keep on assessing the possible relationships among different cytotypes of Astyanax fasciatus (Teleostei, Characiformes) in the Mogi-Guacu River (Sao Paulo State, Brazil), C-banding, chromomycin A 3 staining, and fluorescent in situ hybridization with a repetitive DNA sequence (As51) isolated from Astyanax scabripinnis were performed in the present work. The constitutive heterochromatin was distributed in terminal regions on long arms of submetacentric, subtelocentric, and acrocentric chromosomes and in the terminal region on short arms of a pair of submetacentric chromosomes in both standard cytotypes. This latter heterochromatic site was also GC-rich, as revealed by chromomycin A(3) staining, corresponding to the nucleolar organizer region (NOR), as shown by previous studies. The sites of the satellite As51 DNA were located in terminal regions on long arms of several chromosomes. Some variant karyotypic forms, which diverge from the two standard cytotypes, also presented distinctive chromosomes carrying As51 satellite DNA. It is possible that the standard 2n = 46 cytotype represents an invader population in the Mogi-Guacu River able to interbreed with the resident standard 2n = 48 cytotype. Therefore, the variant karyotypes would be related to a possible viable offspring, where complementary chromosomal rearrangements could favor new locations of the satellite DNA analyzed. Copyright (C) 2008 S. Karger AG, Basel

Cytogenetic characterization of Metynnis maculatus (Teleostei; Characiformes): the description in Serrasalminae of a small B chromosome bearing inactive NOR-like sequences

Mitotic chromosomes of Metynnis maculatus (KNER 1860) (Teleostei, Characiformes), a fish species that occurs in the Amazon and Parana-Paraguay river basins, were analyzed for the first time by Giemsa and Ag-NOR staining, C-banding and fluorescence in situ hybridization (FISH) with 18S and 5S rDNA sequences. The basic chromosome number of the species is 2n=62 (32M+22SM+4ST+4A) and, in addition to the 62 regular chromosomes, one small acrocentric supernumerary B chromosome was found in part of the specimens analyzed. Four active NORs were present, and constitutive heterochromatin blocks were found in the pericentromeric region of several chromosomes. A heterochromatic block was also present in the interstitial portion of the submetacentric NOR-bearing pair and the B chromosome was entirely heterochromatic. FISH using an 18S rDNA probe confirmed the results obtained with AgNO(3) staining, and an additional signal was also present on the B chromosomes. 5S rDNA sequences mapped only to the largest acrocentric pair. This is the first description of supernumerary B chromosomes in Serrasalminae, and this karyotype characterization may be useful in further studies about chromosome evolution in this fish group.