Closely Related Syntopic Cytotypes of Astyanax taeniatus (Jenyns, 1842) from the Upper Piranga River, Upper Doce Basin in Southeastern Brazil

Abstract

Astyanax taeniatus occurs in coastal areas of southeastern Brazil, and it is very abundant in the Upper Doce River Basin. Our objective was to study C-, argyrophilic nucleolar organizer region (Ag-NOR) and fluorescent in situ hybridization (FISH) banding patterns using 5S, 18S, CA(15), and GA(15) repetitive DNA probes on a population of A. taeniatus present in the Piranga River, in the Doce Basin. Two syntopic cytotypes were found, both with 2n = 50: cytotype A (14m + 12sm + 16st + 8t) and cytotype B (10m + 14sm + 18st + 8t). In both cytotypes, heterochromatic blocks occurred in all the chromosomes; Ag-NOR sites were multiple, ranging from four to eight. The 5S rDNA probe marked eight chromosomes in both cytotypes, a unique condition within Astyanax, suggesting a recent divergence between these cytotypes. The 18S rDNA probe differed between the cytotypes, marking 10 and 8 chromosomes in cytotypes A and B, respectively. CA(15) and GA(15) FISH patterns were mainly subtelomeric, but CA(15) showed centromeric markings that were diagnostic for each cytotype. Although overall cytogenetic evidence suggests that these cytotypes are closely related, morphological and molecular data in progress will provide further hypothesis test on their phylogenetic relationship.

Trends in Karyotype Evolution in Astyanax (Teleostei, Characiformes, Characidae): Insights From Molecular Data

“…Smaller variations in the number of 5S rDNA sites can be observed among these species, although they are always located in the proximal or distal region of acrocentric chromosomes, reaching up to 10 markings in A. intermedius and A. giton , which differ by a pericentric inversion ( Kavalco et al, 2004 ). The hypothesis that these characteristics are a symplesiomorphy can be corroborated in independent chromosome data, such as those obtained for A. taeniatus ( Cunha et al, 2016 ), which is also included in the same clade 5 by Rossini et al (2016) . The evolutionary dynamics of this gene are related not only to variations in non-transcribed spacers, but also to syntenia with long and short interspersed nuclear elements, non-long terminal repeat retrotransposons, U-snRNA families, and microsatellite polymorphisms ( Rebordinos et al, 2013 ).…”

Citogenética molecular e evolutiva na família Characidae

“…The most conserved pattern of the 5S rDNA location in fishes is the interstitial region of a single chromosome pair [19]. A similar finding is expected for Astyanax [20], although some species exhibit multiple markings in some chromosome regions [21]. In A. goyacensis, only one chromosome exhibits the syntenic marking of 18S and 5S rDNAs, while the homologue exhibits only 5S rDNA marking.…”

“…8 Astyanax displays wide cytogenetic variation, primarily in the number of chromosomes, karyotype macrostructure, presence of supernumerary chromosomes, heterochromatic block polymorphisms, nucleolus organizer regions (Ag-NORs), variations in the location of ribosomal genes, and triploid syndrome. [9][10][11][12][13][14][15][16][17][18][19] In addition, studies have shown the occurrence of distinct sympatric cytotypes, 6,20 which indicates the diversity of this genus and reinforces the occurrence of cryptic species. However, the amplitude of karyotypic plasticity and specific diversity in Astyanax, as well as its monophyletism are still open questions.…”

Further insights into chromosomal evolution of the genus Enyalius with karyotype description of Enyalius boulengeri Etheridge, 1969 (Squamata, Leiosauridae)

“…The advent of techniques banding heterochromatin regions in DNA is promising for the advance of the comprehension of the genome structure and evolution (Martins et al, 2011). Microsatellite regions apparently accumulate on regions with low levels of replication, such as telomeric and centromeric ones, and are easily detected by Fluorescence in situ Hybridization (FISH) techniques, as indicated in plants, anurans and fishes (Soares-Scott et al 2005;Peixoto et al 2015;Cunha et al 2016). Although cytogenetic studies using molecular tools are still scarce on reptiles, they allow to understand relations between populations or/and species, and identify sexual elements at karyotypic components of species (Martins et al 2011).…”