Liano Centofante

Chromosome polymorphism in Ancistrus cuiabae Knaack, 1999 (Siluriformes: Loricariidae: Ancistrini)

specimens from a bay near the town of Pocone, in thePantanal of Mato Grosso, Brazil. The observed diploid number was 2n = 34 chromosomes for both sexes and three distinctkatyotypic formulae were found, namely cytotype A (20m, 8sm, 6st, Fundamental Number/FN = 68; 6 males and 11 females),cytotype B (19m, 8sm, 6st, 1a, FN = 67; 8 males and 4 females) and cytotype C (18m, 8sm, 6st, 2a, FN = 66; a single male). NORs ’sanalyses showed that these regions were located in distinct sites on the NOR-bearing chromosome pair, according to cytotypes.Thus, in cytotype A, NORs were located in the terminal region of the short arm of the second metacentric chromosome pair; incytotype B, they were detected in the short arm of the metacentric chromosome and interstitially on the acrocentric chromosomeand, in cytotype C, NORs were observed in the interstitial region of the acrocentric chromosome pair. C-positive heterochromati cbands were adjacent to the rDNA sites in the corresponding chromosomes. Thus, the chromosomal polymorphism of

Análise morfométrica em Thoracocharax stellatus (Kner, 1858) (Characiformes, Gasteropelecidae) proveniente de diferentes bacias hidrográficas Sul-americanas

A free-size canonical variable analysis was made to investigate the morphological pattern of variation among different Thoracocharax stellatus populations in South American river basins: Araguaia-Tocantins and Paraguay Basins Rivers from Brazil, and Orinocos basin in Venezuela. Distinction among the samples from Araguaia-Tocantins and Orinoco were observed, with overlap of these populations with the Paraguays basin samples. The primarily characters responsible for this discrimination are head length and dorsal fin length. The mechanisms that can act in this geographic variation among T. stellatus populations are discussed.

Genetic structure of the ornamental tetra fish species Piabucus melanostomus Holmberg, 1891 (CHARACIDAE, IGUANODECTINAE) in the Brazilian Pantanal wetlands inferred by mitochondrial DNA sequences

The subfamily Iguanodectinae comprises a group of small Neotropical fishes composed by two genera and 11 nominal species widely distributed in the Atlantic drainages of South America. Piabucus is the only genus of Iguanodectinae found in the Paraguay River basin, especially in the Pantanal of Mato Grosso State, where it is represented by Piabucus melanostomus. Given the wide distribution and the low dispersion capacity of this species, due the ecological constraints, it is possible that many interesting genetic features could be found in different populations. In this way, the aim of his work was to perform the phylogeographic pattern of P. melanostomus populations using mitochondrial DNA sequences. A total of 13 individuals from three rivers belonging the Mato Grosso wetland were sampled. The ATP sintetase (subunits 6 and 8) gene was completely sequenced, the mean of nucleotide base composition in the sequences was 31.2% (T), 30.2% (C), 26.9% (A) and 11.9% (G), with no gene saturation. The population analysis in the TCS program generated a network with six haplotypes (A to F), where the ancestral haplotype (A) has a frequency of 25% and is composed by individuals from Cuiaba and Paraguay Rivers. The phylogenetic analysis showed the occurrence of two mtDNA lineages (1 and 2), the distance observed between the two lineages was 0.6%. The phylogenetic and phylogeographic results as well as the negative values of Fst for some populations, indicate a possible occurrence of gene flow among the analyzed populations. These results highlights the importance of flood pulse existent on wetland as a vehicle that permits a temporary connection among isolated population maintaining the species genetic variability.

Cytogenetic characterisation of the ornamental freshwater fish, Piabucus melanostomus (Iguanodectinae) from Brazilian wetlands and its relation with species of Characidae basal group

The genus Piabucus is the only member of the subfamily Iguanodectinae found in the Pantanal of Mato Grosso State, where it is represented by Piabucus melanostomus. P. melanostomus from the Paraguay and Bento Gomes Rivers of the Pantanal wetlands were analysed using conventional and molecular cytogenetic techniques to cytogenetically characterise the species and broaden the knowledge of the subfamily. The results indicated no sex-related heteromorphisms. The diploid number for the species was 2nxa0=xa050 chromosomes, which were divided into six metacentric, eight submetacentric, 24 subtelocentric, and 12 acrocentric with a fundamental number (FN) of 88. Heterochromatin was visualised using the C-banding technique, which showed that it was mainly distributed in the centromeric and pericentromeric region of most chromosomes, but larger blocks were observed on the long arms of large subtelocentric chromosomes (8, 9, 10, 13, and 20 pairs). Nucleolar organising regions (Ag-NOR) were observed in the p-subterminal region of one subtelocentric chromosome pair (9) with a remarkable size polymorphism between homologues in individuals from the Paraguay River, which was confirmed using the FISH technique with 18S rDNA. In this population, in all individuals studied, one of the homologous shows block considerably larger. The karyotype was compared with those of other subfamilies considered basal in Characidae, according to morphological data.

Microstructural chromosome reorganization in the genus Trichomycterus (Siluriformes: Trichomycteridae)

Trichomycterus is a specious fish genus within Trichomycterinae and displays remarkable karyotype diversity. However, knowledge about their genomic structure and location of repetitive sequence is still limited. In order to better understand the karyotype diversification, we analyzed nine species of Trichomycterus using classical and molecular cytogenetic techniques. Results revealed a conserved diploid chromosome number of 2n=54 chromosomes in all analyzed species, although remarkable differences on the constitutive heterochromatin distribution were observed. In addition, while the 18S rDNA showed a conserved distribution pattern, the 5S rDNA sites showed a quite diverse location considering the analyzed species. Remarkably, both ribosomal genes were co-located in all species, except in T . iheringi , suggesting that co-localization is probably an ancestral condition in Trichomycterus . Finally, three analyzed species showed heterochromatic B chromosomes, reinforcing the intense genomic reorganization occurring in Trichomycterus . Our results showed that chromosomal variations are not restricted to differences in karyotype formula as previously proposed, but also to modifications on the microstructural level of resolution.

Molecular Clock as Insight to Estimate the Evolutionary History and Times of Divergence for 10 Nominal Astyanax Species (Characiformes, Characidae): An Evolutionary Approach in Species with 2n = 36, 46, 48, and 50 Chromosomes

Astyanax is a genus with a wide distribution ranging from the south United States to north of Patagonia (Argentina). The available cytogenetic data on Astyanax indicate a high karyotypic diversity, with diploid number of 36-52 chromosomes, presence of B chromosomes, heterochromatin polymorphism, and variations with respect to the number and localization of nucleolar organizer regions (NORs) and 18S and 5S ribosomal DNA sites. In the present study, we estimated the evolutionary history and times of divergence for 10 nominal Astyanax species from the South and Central/North American (Cna) continents, which present distinct chromosomal characteristics, based on molecular clocks inferred from mitochondrial DNA sequence. The molecular clock results indicate the origin of three distinct clades (Humeral dark spot [Hds]; Diffuse humeral spot [Dhs]; Cna group) during the late Miocene about 11.2 million years ago (Mya). Thus, Astyanax mexicanus (Cna) represent a species that diverged a long time ago (∼8.6u2009Mya) from the Hds group, and Astyanax schubarti is the oldest species (∼6.5u2009Mya) among the Dhs species.

Comparative cytogenetics of Astyanax (Teleostei: Characidae) from the upper Paraguay basin

Astyanax is one of the most abundant and diverse taxa of fishes in the Neotropical region. In order to increase the amount of cytogenetic information for Astyanax as well as to exhibit data to subsidize future taxonomic studies, this work analyzed three species of Astyanax: two species are cryptic, and are here reported to live in syntopy (A. abramis and A. lacustris); the first karyotype description for A. pirapuan is also presented. Cytogenetic analyzes reveal a diploid number of 2n=50 chromosomes for three species, yet with differences in their karyotype morphology. The physical mapping of 18S rDNA showed up to thirteen sites in A. pirapuan and two in A. abramis and A. lacustris. The physical mapping of 5S rDNA has proven to be an effective marker for the characterization of species of Astyanax studied in this work.

Chromosomal organization of retrotransposon Rex1 in Astyanax species (Characiformes, Characidae)

Abstract The cytogenetic studies of retrotranposons Rex have been characterized in several fish groups, including species of the Astyanax genus. This group presents an extensive variability in their karyotype, with diploid numbers of 2n = 52, 50, 48, 46 and 36 chromosomes. Thus, the aim of this study was to evaluate the distribution of the retrotransposable element Rex1, in six Astyanax species, with different diploid numbers. The species analyzed were Astyanax altiparanae (2n = 50), Astyanax asuncionensis (2n = 50), Astyanax eigenmanniorum (2n = 50), Astyanax marionae (2n = 48), Astyanax fasciatus (2n = 46) and Astyanax schubarti (2n = 36). Rex1 was dispersed in the Astyanax species, suggesting that these retrotransposons play important role in genome evolution.

Distinct classical and molecular cytogenetics of Astyanax marionae and A. fasciatus (Characiformes: Characidae): a comparative study of the organization of heterochromatin and repetitive genes

Genus Astyanax is well distributed in Neotropical freshwater environments and its taxonomic position is uncertain, as is the case with other Characidae genera allocated in the group incertae sedis. This study aimed to analyse the karyotype of different populations of Astyanax fasciatus (Corumbataí River basin) using Giemsa staining, C-band technique, and fluorescence in situ hybridization for the H3 histone and 5S rRNA genes, in addition we describe for the first time the chromosomal organization of H3 histone and 5S rRNA genes in A. marionae (Paraguay River basin). Chromosomes of three A. fasciatus populations were analysed (two with