Chromosomal Microstructure Diversity in Three Astyanax (Characiformes, Characidae) Species: Comparative Analysis of the Chromosomal Locations of the 18S and 5S rDNAs

Abstract

The species of genus Astyanax is widely distributed in freshwater neotropical zones. Astyanax is considered to be taxonomically confused, similar to other genera placed incertae sedis in Characidae. The cytogenetics of this genus is well characterized; species vary widely in diploid number, from 2n=36 chromosomes in Astyanax schubarti to 2n=50 for most species studied. The size, number, and position of different cytological markers vary among species and populations of Astyanax. We analyzed the karyotypes of individuals from three Astyanax species (Astyanax abramis, Astyanax altiparanae, and Astyanax eigenmanniorum) from populations not previously analyzed. We describe variations in several cytogenetic markers and the karyotypic relationships between them, specifically focusing on the characteristics of the conserved and divergent locations of the ribosomal genes. Our data are useful for establishing relationships between species and for investigating the karyotype evolution within the genus.

Highly Similar Morphologies Between Chromosomes Bearing U2 snRNA Gene Clusters in the Group Astyanax Baird and Girard, 1854 (Characiformes, Characidae): An Evolutionary Approach in Species with 2n = 36, 46, 48, and 50

“…26 The form found in most species, including the A. fasciatus karyomorphs analyzed here, exhibits one metacentric pair and one acrocentric or subtelocentric pair with 5S rDNA sites located on the long arm, both near the centromere. 26 According to Vicari et al, 27 Astyanax species with two chromosome pairs bearing 5S rDNA sites exhibit probable synapomorphic features.…”

Cytogenetic and Molecular Data SuggestDeuterodon pedriEigenmann, 1907 (Teleostei: Characidae) Is a Member of an Ancient Coastal Group

“…48 Transposable elements may insert at 18S loci and transfer these sequences to other chromosomes, resulting in the relocation of these cistrons on different chromosome pairs. 49 In D. pedri, the 5S rDNA is restricted to a pair of subtelocentric chromosomes, a pattern that also occurs in A. altiparanae. 50 However, in most of Astyanax species, the 5S gene region typically occurs in two pairs of homologous chromosomes: in the proximal region of a metacentric chromosome pair, 34,51,52 and in the telomeric region of an acrocentric chromosome pair.…”

“…10,47 Astyanax species present high variety of numbers of 18S rDNA markers. 10,34,37,46,48,49 The divergence in the locations of 18S rDNA sequences among some species might be explained by the evolutionary effect of transposable elements activities. Chromosomal terminal regions can promote transposition events, leading to the dispersal of DNA segments.…”

Chromosomal mapping of H3 histone and 5S rRNA genes in eight species of Astyanax (Pisces, Characiformes) with different diploid numbers: syntenic conservation of repetitive genes

“…These genes can characterize groups being located in one chromosome pair as in the genus Apareiodon (Parodontidae) (Vicari et al 2006;Rosa et al 2006;Bellafronte et al 2009Bellafronte et al , 2011, or distributed in one or more pairs, ranging numerically depending on the population studied, as shown in Astyanax scabripinnis (Characidae) (Ferro et al 2001;Almeida-Toledo et al 2002;Santos et al 2012). The chro-mosomal locations of 5S ribosomal DNA (rDNA) sequences are well conserved in species of the genus Astyanax; this contrasts with 45S rDNA locations, which are remarkably variable (Piscor et al 2015).…”