Comparative cytogenetic survey of the giant bonytongue Arapaima fish (Osteoglossiformes: Arapaimidae), across different Amazonian and Tocantins/Araguaia River basins

The South American giant fishes of the genus Arapaima, commonly known as pirarucu, are one of the most iconic among Osteoglossiformes. Previously cytogenetic studies have identified their karyotype characteristics; however, characterization of cytotaxonomic differentiation across their distribution range remains unknown. In this study, we compared chromosomal characteristics using conventional and molecular cytogenetic protocols in pirarucu populations from the Amazon and Tocantins-Araguaia river basins to verify if there is differentiation among representatives of this genus. Our data revealed that individuals from all populations present the same diploid chromosome number 2n=56 and karyotype composed of 14 pairs of meta- to submetacentric and 14 pairs of subtelo- to acrocentric chromosomes. The minor and major rDNA sites are in separate chromosomal pairs, in which major rDNA sites corresponds to large heterochromatic blocks. Comparative genomic hybridizations (CGH) showed that the genome of these populations shared a great portion of repetitive elements, due to a lack of substantial specific signals. Our comparative cytogenetic data analysis of pirarucu suggested that, although significant genetic differences occur among populations, their general karyotype patterns remain conserved.(AU)

Os peixes gigantes da América do Sul do gêneroArapaima, comumente conhecidos como pirarucus, são um dos mais icônicos de Osteoglossiformes. Estudos citogenéticos prévios identificaram suas características cariotípicas, entretanto a caracterização da diferenciação citotaxonômica através de suas distribuições geográficas ainda são desconhecidas. Nesse estudo, nós comparamos características cromossômicas utilizando técnicas de citogenética clássica e molecular em populações das bacias dos rios Amazonas e Tocantins-Araguaia, a fim de verificar se há alguma diferenciação entre representantes desse gênero. Nossos dados revelaram que indivíduos de todas as populações apresentam número diploide de 2n=56 cromossomos e que seus cariótipos são compostos de 14 pares de cromossomos meta- e submetacêntricos e 14 pares de subtelo- e acrocêntricos. Os sítios maiores e menores de rDNA estão localizados em pares cromossômicos separados, onde os sítios maiores de rDNA correspondem a grandes blocos heterocromáticos. Hibridizações genômicas comparativas (CGH) mostraram que o genoma dos espécimes dessas populações é amplamente compartilhado, devido à falta de sinais substanciais específicos. Nossos dados de citogenética comparativa do pirarucu sugerem que embora diferenças genéticas significativas ocorram entre populações, os padrões cariotípicos gerais se mantêm conservados.(AU)

Coexistence of cytotypes and chromosomal mosaicism in Hoplias malabaricus (Characiformes, Erythrinidae)

Karyotypes of seventeen Hoplias malabaricus specimens, collected in the fish culture station of UNOPAR (University of Northern Paraná), were analyzed. The station is in the Claro River system in the Tibagi River basin. Two distinct and coexistent karyotype forms (cytotypes) were identified, comprising either 42 chromosomes (cytotype A) or 40 chromosomes (cytotype C), both presenting metacentric and submetacentric chromosomes. In two specimens, one male and one female, it was not possible to characterize a modal diploid number because different cell lines were observed, with a predominance of 2n=41 and 2n=42 chromosomes at a frequency of 38.24 percent and 41.12 percent, respectively. The karyotype with 2n=41 showed some putative monosomic and trisomic chromosomes, while the karyotype with 2n=42 showed 21 chromosomal pairs, similar to cytotype A. RAPD analysis showed that these two specimens have the same band pro file of cytotype A (Nei's genetic identity=92 percent), discarding a possible hybridization between both cytotypes and supporting the mosaicism hypothesis. These findings corroborate the isolation between cytotypes A and C.

Cytogenetic and comparative morphology of two allopatric populations of Astyanax altiparanae Garutti & Britski, 2000 (Teleostei: Characidae) from upper rio Paraná basin

The recently described fish species, Astyanax altiparanae (tetra) is common in the upper rio Paraná basin, and has been reported in the Iguaçu basin. However, its natural origin in the rio Iguaçu is questionable. In the present work, karyotypical and morphological features of two populations of Astyanax altiparanae from the upper rio Tibagi and upper rio Iguaçu were compared. Both populations showed 2n=50 chromosomes and differences in their karyotype formula, NOR-bearing chromosomes and location of heterochromatin. Morphometric data from both populations were analyzed through free-size canonical variables. Cytogenetic and morphological results were mostly coincident showing exclusive markers that reflect their degree of populational isolation. In addition to other geographic, morphological and molecular data for A. altiparanae populations from the lower rio Iguaçu and rio Paraná tributaries upstream from the Itaipu Dam (South Brazil), the present results indicate that the two populations analyzed in this study belong to different stocks. The presence of this species along the rio Iguaçu basin would be a consequence of a complex and poorly understood evolutionary history.

Astyanax altiparanae, recentemente descrita, é comum na bacia do alto rio Paraná, tendo sido registrada recentemente na bacia do rio Iguaçu. Entretanto, sua origem natural no rio Iguaçu é questionável. No presente trabalho algumas características cariotípicas e morfológicas de duas populações de Astyanax altiparanae do rio alto rio Tibagi e alto rio Iguaçu foram comparadas. Ambas as populações mostraram 2n=50 cromossomos e diferenças nas suas fórmulas de cariotípicas, cromossomos portadores das regiões organizadoras de nucléolos e localização da heterocromatina. Dados morfométricos das duas populações foram analisados para variáveis canônicas livres de tamanho. Os dados citogenéticos e morfológicos foram coincidentes e mostraram marcas exclusivas que refletem o grau de isolamento populacional. Em adição a outros dados geográficos, morfológicos e moleculares em populações de A. altiparanae do baixo rio Iguaçu e tributários do rio Paraná acima da represa de Itaipu (Sul do Brasil), os presentes resultados indicam que as duas populações analisadas neste estudo pertençam a diferentes estoques. A presença desta espécie ao longo da bacia do rio Iguaçu pode ser uma conseqüência de uma história evolutiva complexa e pouco conhecida.

Intra- and inter-individual chromosome variation in Hoplerythrinus unitaeniatus (Pisces, Erythrinidae): a population from the Brazilian São Francisco river basin

Chromosomal studies were carried out on a population of the fish Hoplerythrinus unitaeniatus (jeju) from Prata river in the São Francisco river basin, Minas Gerais, Brazil using conventional Giemsa staining, C-banding, silver nitrate nucleolar organizer region (Ag-NOR) staining and fluorescent in situ hybridization (FISH) with 18S and 5S rDNA probes. We found a high degree of inter- and intra-individual variability with the identification of 2n = 50, 2n = 51 and 2n = 52 karyotypes at nearly the same frequency within the population. Intra-individual variation in chromosomal morphology and, consequently, karyotype formulae was also observed, chiefly in the specimens with 2n = 50 and 2n = 52 chromosomes. Ag-NORs and 18S rDNA sites also showed numerical and chromosomal variation similar to that found for the 5S rDNA sites. Some putative hypotheses are considered in order to explain these results.

A simple method for fresh-weter fish lymphocyte culture

No presente trabalho descreve-se uma técnica de cultura de linfócitos, em sangue periférico total, aplicável aos estudos de Citogenética de peixes. Esta metodologia, relativamente simples, tem apresentado uma alta repetibilidade e produzido preparaçöes cromossômicas de boa qualidade