A comparative structural cytogenetic study in three allopatric populations of Astyanax scabripinnis (Teleostei: Characidae)

Abstract

ABSTRACT. Individual samples from five populations of the characid fish Astyanax scabripinnis (Jenyns, 1842) from the Tietê and Paranapanema river basins (Brazil) were studied. All individuals analyzed presented 50 chromosomes but three different karyotypic forms were observed. Additionally, some individuals of one karyomorph presented a macro supernumerary chromosome. No chromosomal differentiation was observed between males and females in any sample analyzed. C-banding revealed two distinct distribution patterns in these populations in which strong terminally located heterochromatic blocks were detected in the long arms of some chromosomes of the specimens from Cascatinha, Cintra, and Funari streams, whereas populations of the Capão Bonito stream and the Barbosa waterfall revealed less evident heterochromatic blocks on the chromosomes. The comparative study of the 18S rDNA localization by fluorescent in situ hybridization, and detection of active nucleolus organizing regions by silver stain (Ag-NORs) showed differences in rDNA content and expression of this gene site among the individuals analyzed. Chromosome mapping of the 5S rDNA revealed the presence of four sites located in two distinct chromosomal pairs, with no apparent differences among karyomorphs. Based on the biogeographical distribution and specific biological characteristics of the species, the data focus on the chromosome differentiation mechanisms involved in the speciation process acting on the populations of the Astyanax scabripinnis species complex.

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

“…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.…”

Karyotypic diversity among three species of the genus Astyanax (Characiformes: Characidae)

“…A large supernumerary or B chromosome, similar to that found in the population from Itiz stream, has been observed in several populations of A. scabripinnis (Néo et al, 2000;Maistro et al, 2001;Ferro et al, 2003;Fernandes and Martins-Santos, 2005;Santos et al, 2012). The first approach on the probable origin of this chromosome was performed by Salvador and Moreira-Filho (1992), who considered that a non-disjunction, followed by heterochromatinization, could be associated with its emergence.…”

“…While the "scabripinnis complex" has been characterized by a preferential centromeric and telomeric pattern of C-bands (Fernandes and Martins-Santos, 2005;Souza et al, 2007;Santos et al, 2012), the "bimaculatus group" has shown mainly interstitial heterochromatic blocks on the chromosomes (Domingues et al, 2007;Hashimoto et al, 2008;Ferreira Neto et al, 2009;Kavalco et al, 2011). The species now analyzed show that the distribution of heterochromatin falls, in general, among the above cases.…”

“…According to these authors, the number of the species in this complex is subestimated. As a whole, the available data indicate that the karyotype evolution in this fish group is very dynamic and goes beyond the 'simple' accumulation of chromosomal rearrangements (Santos et al, 2012).…”

“…Astyanax have presented an extensive diversity in the chromosome number and karyotype formula, both intra-and interspecifically, besides the occurrence of B chromosomes and natural polyploidy for some populations (Malacrida et al, 2003;Gross et al, 2004;Kantek et al, 2007;Peres et al, 2009;Santos et al, 2012).…”