B chromosomes in a population of Astyanax eigenmanniorum (Characiformes, Characidae) from the Araguari River Basin (Uberlândia, MG, Brazil)

Abstract

A cytogenetic study was conducted on an Astyanax eigenmanniorum population from the Caetano Stream (18°44' 56" S/ 048°18' 39" W) -in Uberlândia, MG, Brazil -showing a modal diploid number of 48 chromosomes in the standard male and female karyotypes. However, in several specimens it was also possible to observe metaphases with one or two B chromosomes, increasing the diploid number to 49 or 50 chromosomes, respectively. The supernumerary chromosomes were totally heterochromatic and highlighted after C-banding. The silver-stained nucleolus organizing regions (Ag-NORs) were located in at least five chromosomes of the standard karyotype, thus characterizing a multiple NOR system in the species. This is the first occurrence of an A. eigenmanniorum population with 2n = 48 chromosomes, bearing supernumerary chromosomes.

Karyotype diversity of four species of the incertae sedis group (Characidae) from different hydrographic basins: analysis of AgNORs, CMA3 and 18S rDNA

“…Another population of Astyanax eigenmanniorum, from Caetano stream, Uberlandia/MG, analyzed by Torres-Mariano and Morelli (2008), showed a formula of 14m + 18sm + 10st + 6a, constituted by a greater number of meta-and submetacentric chromosomes (32), compared with the results obtained in this study (26 chromosomes). Torres-Mariano and Morelli (2008) also found 0 to 2 B chromosomes which were not observed in the population studied here.…”

“…Torres-Mariano and Morelli (2008) also found 0 to 2 B chromosomes which were not observed in the population studied here. In Astyanax eigenmanniorum of Laguna dos Patos, the first metacentric pair did not show a size much greater than that of the other chromosomes of the complement, which is a characteristic that is shared by many characids and that was observed in the population studied by Torres-Mariano and Morelli (2008).…”

“…In relation to heterochromatin, the population of Astyanax eigenmanniorum of Laguna dos Patos showed the weak presence of heterochromatin in the pericentromeric region of all chromosomes, while A. eigenmanniorum of Caetano stream/MG displayed heterochromatin distributed in the terminal and/or centromeric regions (Torres-Mariano and Morelli, 2008). Observing the karyotypic differences found between the population of Astyanax eigenmanniorum in the present study and the population of the Caetano stream /MG suggests that the latter probably belongs to a different species, because the karyotype differences found between these two populations corroborate what was described by Lima et al (2003), limiting the occurrence of A. eigenmanniorum to the southern region of Brazil.…”

First description of B chromosomes in the Hyphessobrycon (Characiformes, Characidae) genus: a hypothesis for the extra element of Hyphessobrycon eques Steindachner, 1882

“…The B chromosomes have been described in many neotropical fish groups (see, for example, Maistro et al 1992, Oliveira et al 1997, Maistro et al 2000, Torres-Mariano and Morelli 2008, Ferreira-Neto et al 2012, Hashimoto et al 2012, Silva et al 2014). The occurrence of this type of chromosome among individuals of a population can be sporadic or commonly found for many individuals, and high frequency can be shown between them.…”

Establishment of rapid and non-invasive protocols to identify B-carrying individuals of Psalidodon paranae

“…During the preceding decades, the large metacentric B chromosome variant, or the macro-B chromosome, observed in seven species of Psalidodon , was analyzed using distinct approaches ( Maistro et al , 1992 ; Salvador and Moreira-Filho, 1992 ; Moreira-Filho et al , 2001 ; Torres-Mariano and Morelli, 2008 ; Silva et al , 2016 ). These species were originally part of the Astyanax genus, but a recent revision led to their inclusion in the Psalidodon genus ( Terán et al , 2020 ).…”