title: Epifluorescence and light microscopy evidencing structural and functional polymorphism of ribosomal DNA in fish (Teleostei: Astyanax fasciatus).
abstract: New karyotypic data are presented for the Astyanax fasciatus species complex from four different locations on the Upper Tibagi River in the state of Paraná, Brazil. Chromosome markers were analyzed using conventional (Ag-NOR) and molecular (FISH with 18S biotinylated probes) methods. Two cytotypes were found in cell counts with diploid number 2n=48 chromosomes and 2n=50 chromosomes, previously denominated Cytotype A and B, respectively. Two specific patterns of Ag-NORs markers (ribosomal gene activity) were found, with intra-population and inter-population variations. Cytotype A exhibited two to three chromosomes with NOR sites in the metaphases analyzed. In Cytotype B specimens, up to three markers were found, demonstrating greater intra-population and inter-population variation. All individuals with only one chromosome pair with NORs were located in the telomeric region of the short arm of Chromosome 5. This characteristic was interpreted as ancestral for the species. Another identified pattern revealed a site in the telomeric region probably in the long arm of Chromosome 4 and another submetacentric chromosome with bitelomeric marks exclusively in specimens with 2n=50 chromosomes. In the FISH analysis (ribosomal gene structure), five to seven markers were identified in Cytotype A and three to seven markers were identified in Cytotype B. Structural chromosome events and/or transposable elements are required to explain the ribosomal gene location diversity in these organisms. The results of the present study corroborate the hypothesis that the A. fasciatus of the Upper Tibagi River region constitute a species complex.
authors.affiliation: Universidade Estadual de Ponta Grossa, Departamento de Biologia Estrutural, Molecular e Genética, Av. Carlos Cavalcanti, 4748. 84030-900 Ponta Grossa-PR, Brazil. rfartoni@pesquisador.cnpq.br
authors.forename: Roberto Ferreira
authors.initials: RF
authors.lastname: Artoni
authors.forename: Maria Cláudia
authors.initials: MC
authors.lastname: Gross
authors.forename: Carlos Henrique
authors.initials: CH
authors.lastname: Schneider
authors.forename: Marcelo Ricardo
authors.initials: MR
authors.lastname: Vicari
authors.forename: Mara Cristina
authors.initials: MC
authors.lastname: de Almeida
authors.forename: Daniele Aparecida
authors.initials: DA
authors.lastname: Matoso
mesh_terms: D000818:Animals; D004275:DNA, Ribosomal / Q000737:chemistry* / Q000502:physiology; D005260:Female; D005399:Fishes / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008856:Microscopy, Fluorescence; D009697:Nucleolus Organizer Region / Q000648:ultrastructure; D020161:Physical Chromosome Mapping; D011110:Polymorphism, Genetic
chemical_list: D004275:DNA, Ribosomal