Chromosome polymorphism in <i>Astyanax fasciatus</i> (Teleostei, Characidae). 1. Karyotype analysis, Ag-NORs and mapping of the 18S and 5S ribosomal genes in sympatric karyotypes and their possible hybrid forms

Vol. 112, No. 3-4, 2006

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Original Article

Chromosome polymorphism in Astyanax fasciatus (Teleostei, Characidae). 1. Karyotype analysis, Ag-NORs and mapping of the 18S and 5S ribosomal genes in sympatric karyotypes and their possible hybrid forms
R. Pazza^a, K.F. Kavalco^b, L.A.C. Bertollo^a

^a Universidade Federal de São Carlos, Departamento de Genética e Evolução, São Carlos, SP,
^b Universidade de São Paulo, Departamento de Genética e Biologia Evolutiva, São Paulo, SP (Brazil)

Address of Corresponding Author

Cytogenet Genome Res 2006;112:313-319 (DOI: 10.1159/000089886)

Abstract.

Astyanax fasciatus may be characterized as a chromosomally diversified 'species' presenting distinct cytotypes, each with its specific variants. The sympatric and syntopic occurrence of different cytotypes reinforces the hypothesis in which A. fasciatus may represent a group of species currently placed under a single common designation. Specimens from three collection points spread along the Mogi-Guaçu River in southeast Brazil were examined in the present work: (1) near its headwaters (Ouro Fino - MG), (2) in the middle region of the river (Cachoeira de Emas, Pirassunun ga - SP) and (3) close to its confluence with the Pardo River (Barrinha - SP). The 2n = 48 chromosomes cytotype was found in all sampling points, while cytotype 2n = 46 was only encountered in Barrinha and Cachoeira de Emas. In the latter locality, cytotype 2n = 46 predominated; nevertheless, other karyotype forms with 2n = 45 and 47 chromosomes also occurred, besides a structural variant of cytotype 2n = 46. One specimen with 2n = 47 chromosomes was also found in Ouro Fino. The Ag-NOR analysis, as well as the location of the 18S and 5S ribosomal genes, were conserved in all cytotypes. The data indicate that the variant karyotypes are a consequence of interbreeding between the standard cytotypes (2n = 46 and 48) and/or its descendants. This suggests a karyotype plasticity for this species, where at least a few variant karyotypes would not have deleterious effects on their bearers.

Author Contacts

Request reprints from Dr. Rubens Pazza

UFSCar - Universidade Federal de São Carlos

Departamento de Genética e Evolução

Rodovia Washington Luís, km 235

CP 676, 13565-905, São Carlos, SP (Brazil)

telephone: +55 16 3351 8309 and +55 16 3351 8787

fax: +55 16 3351 8377; e-mail: pazza@biociencia.org

Article Information

Supported by FAPESP (Proc. 01/02777-5) and the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico).

Manuscript received: 20 April 2004
Accepted in revised form for publication by M. Schmid,: 29 July 2005.
Number of Print Pages : 7
Number of Figures : 5, Number of Tables : 2, Number of References : 59

Medline Abstract (ID 16484788)

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