Cytogenetic analysis of Astyanax laticeps (Cope, 1894) (Ostariophysi: Characidae) from the laguna dos Patos system

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Abstract

The genus Astyanax is prominent among Characiformes, due to the large number of species found and its wide geographic distribution. In this work, Astyanax laticeps specimens from the laguna dos Patos system were cytogenetically analyzed. A diploid number of 2n = 50 chromosomes distributed into 6m+16sm+16st+12a (FN = 88) was found, without differences between males and females. A few small heterochromatin blocks were observed, besides three more conspicuous C-bands, corresponding to NORs, as confirmed by silver nitrate and CMA3 staining, FISH, and DAPI negative staining. These regions were located in a medium-sized subtelocentric and in a large subtelocentric chromosomal pair, probably because of a deletion of this region in one homologous chromosome, or due to a transposition event between them.

Translated abstract

O gênero Astyanax é destacado entre os Characiformes, pelo grande número de espécies encontradas e a ampla distribuição geográfica. Neste trabalho, foram analisados citogeneticamente espécimes de Astyanax laticeps do sistema da laguna do Patos. O número diplóide observado foi de 2n = 50 cromossomos distribuídos em 6m+16sm+16st+12a (NF= 88), sem diferenças entre machos e fêmeas. Foram observados poucos blocos de heterocromatina, além de três bandas-C mais conspícuas, correspondentes às NORs, confirmado pela coloração com nitrado de prata,CMA3, FISH, e coloração negativa ao DAPI. Estas regiões foram localizadas em um cromossomo subtelocêntrico de tamanho médio e em um par subtelocêntrico grande, provavelmente devido a deleção desta região em um dos cromossomos homólogos, ou por eventos de transposição entre eles

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Most cited references 32

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A simple technique for demonstrating centromeric heterochromatin.

A.T. Sumner (1972)

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Reverse fluorescent chromosome banding with chromomycin and DAPI.

D Schweizer (1976)

Two DNA binding guanine-specific antibiotics, chromomycin A3 (CMA) and the closely related mithramycin (MM), were used as chromosome fluorescent dyes. Root-tip metaphase chromosomes of three plant species and human metaphase chromosomes were sequentially stained with CMA or MM and the DNA binding AT-specific fluorochrome 4'-6-diamidino-2-phenylindole (DAPI). In some cases a non-fluorescent counterstain was used as contrasting agent: methyl green in conjunction with CMA, and actinomycin D (AMD) in combination with DAPI.--In all three plant species, Vicia faba, Scilla siberica, and Ornithogalum caudatum, the nucleolus organiser regions and/or associated heterochromatin displayed very bright fluorescence with CMA and MM and, in general, heterochromatic segments (C-bands) which were bright with CMA and MM were pale with DAPI whereas segments which were dim with CMA and MM displayed very bright fluorescence with DAPI.--Human metaphase chromosomes showed a small longitudinal differentiation in CMA fluorescence, which was essentially the reverse of the banding pattern obtained with AMD/DAPI double-staining, but of lower contrast. The cma-banding pattern appears to be similar to the pattern found by R-banding procedures.

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Two new species of Astyanax (Ostariophysi: Characiformes: Characidae) from eastern Brazil, with a synopsis of the Astyanax scabripinnis species complex

Vinicius Bertaco, Carlos Lucena (2006)

Two new species of Astyanax are described from eastern Brazil: A . microschemos from the córrego Palmital, rio Itapemirim drainage, Espírito Santo, and A . pelecus from the rio Pardo drainage, Bahia. Astyanax microschemos differs from its congeners by its shallower body depth, 26.9-29.7% of standard length, the presence of one vertically elongate humeral spot that extend above and below the lateral line, smaller interorbital width, 26.9-30.4% of head length, and the possession of 14-18 branched anal-fin rays. Astyanax pelecus differs from its congeners in the possession of only one humeral spot limited to the region dorsal to the lateral line, conspicuous, dark, midlateral body stripe extending from the upper margin of the opercle to the caudal-fin base, a shallower body depth, 26.7-34.8% of standard length, and the possession of 16-18 branched anal-fin rays, 38-39 scales in the lateral-line series, and four scales between the lateral line and the pelvic-fin origin. Astyanax microschemos has a massive head, short snout, usually smaller than the orbital diameter, shallow body depth, and vertically-elongate humeral spot that serve to include it in the A . scabripinnis species complex. A comparative synopsis of this complex is provided.