Variação cariotípica de Astyanax bimaculatus (Linnaeus, 1758) (Pisces: Characidae) nas bacias costeiras do Brasil / Karyotypic variation of Astyanax bimaculatus (Linnaeus, 1758) (Pisces: Characidae) in the coastal basins of Brazil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The genus Astyanax comprises 90 species considered together with most of the old Tetragonopterinae as incertae sedis within the family Characidae. Most of the Astyanax are small, were classified in an artificial taxonomic system and therefore their taxonomic boundaries are poorly defined. Seven coastal populations of one of these species, Astyanax bimaculatus were studied cyotgenetically with conventional (Giemsa) stain, heterochromatin was evidenced with C- banding, nucleolar organizing regions and associated guanine- cytosine-rich regions were evidenced with silver nitrate and chromomycine A3. All populations are from southeastern Brazil: one in Pardo River, five in the Doce basin including four Quaternary lakes and a population in the headwaters of the Piranga River and one population from the Carangola River in the Paraíba do Sul basin. All populations shared the same 2n=50 diploid number and chromosome morphology comprising 6 metacentric, 20 submetacentric , 18 subtelocentric and 6 telocentric chromosomes, and one pair of NORs located in a pair of subtelocentrics. However, populations were characterized by high levels of variation of heterochromatic regions. All these character states were shared with Astyanax lacustris from the São Francisco River. This karyotypic stability stands in sharp contrast with the one reported in populations of this species complex in the Upper Paraná, today described as Astyanax altiparanae. It is suggested that the observed patterns are due to the relative geographic isolation of the coastal populations and that at least part of the high karyotypic variability that characterizes A. altiparanae may be explained by secondary contact between Upper Paraná and coastal populations. Finally, variation of heterochromatic blocks suggests that Quaternary isolation has not favored chromosomal speciation.

ASSUNTO(S)

cytogenetics heterocromatina astyanax bimaculatus zoologia astyanax bimaculatus citogenética heterochromatin

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