Comparative cytogenetics in Astyanax (Characiformes: Characidae) with focus on the cytotaxonomy of the group

Abstract

Astyanax is a diverse group of Neotropical fishes, whose different forms occupy different environments. This great diversity is also reflected on cytogenetic aspects and molecular markers, which have repeatedly been demonstrated by cytogenetic studies. In order to characterize the karyotype of species of this genus, six species were studied: Astyanax altiparanae, A.argyrimarginatus, A. elachylepis, A. xavante, and two new species provisionally called Astyanax sp. and A. aff. bimaculatus. A detailed cytogenetic study based on conventional staining with Giemsa, AgNORs, C-banding, base-specific fluorochromes, and FISH using ribosomal genes 18S and 5S was conducted, aiming to understand some of the chromosomal mechanisms associated with the high diversification that characterizes this group and culminated with the establishment of these species. The results showed 2n = 50 chromosomes for five species and a karyotype with 52 chromosomes in Astyanax sp. Small variations in the macrostructure of the karyotypes were identified, which were quite relevant when analyzed by classical banding, fluorochromes, and FISH methods. These differences among Astyanax spp. (2n = 50) are largely due to changes in the amount and types of heterochromatic blocks. Astyanax sp (2n = 52), in addition to variations due to heterochromatic blocks, has its origin possibly by events of centric fission in a pair of chromosomes followed by minor rearrangements.These results show an interesting karyotypic diversity in Astyanax and indicate the need of a review of the group referred as A. aff. bimaculatus and the description of Astyanax sp., including the possibility of inclusion of this unit in another genus.

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

“…The genus Astyanax displays variability among species with respect to chromosome structure, number, and morphology (see, for example, Morelli et al 1983;Almeida-Toledo 2001, 2005;Tenório et al 2013). However, the current study showed that the H3 histone gene locations were conserved among species, particularly with Fig.…”

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

“…Other authors described different numbers of chromosomes bearing NORs in the genus Astyanax. 6,10,[22][23][24][25] According to Tenório et al, 11 six Astyanax species had different Ag-NOR numbers. One pair was observed in Astyanax argyrimarginatus, Astyanax aff.…”

“…Among Astyanax species, and among populations of the same species, these markers have both conserved and divergent features. [9][10][11][12] In this study, we used various cytogenetic markers to obtain new chromosomal data for A. altiparanae and Astyanax eigenmanniorum, and to describe, for the first time, the karyotype of Astyanax abramis. Our findings contribute to the understanding of chromosomal evolution in the genus Astyanax.…”

Origin of B chromosomes in the genus Astyanax (Characiformes, Characidae) and the limits of chromosome painting

“…To date, several classes of repetitive DNAs have been physically mapped in different Astyanax species, providing important clues about karyotype diversification at intra and inter-specific levels (Kavalco and Moreira-Filho 2003;Kavalco et al 2011Kavalco et al , 2012Hashimoto et al 2011;Pansonato-Alves et al 2013;Silva et al 2013;Tenório et al 2013). For instance, the chromosomal location of 5S rDNA and H1 histone sites is remarkably conserved in different species (Mantovani et al 2005;Hashimoto et al 2011).…”