Natural triploidy inAstyanax scabripinnis(Pisces, Characidae) and simultaneous occurrence of macro B-chromosomes

Abstract

The occurrence of natural triploidy in two specimens of Astyanax scabripinnis collected in the Araqua river and in the C6rrego das Pedras stream, respectively, is noticed. The triploid specimen from the Araqua river presented one macro B-chromosome and the triploid specimen from C6rrego das Pedras stream presented two macro B-chromosomes. The C-banding performed in the specimen from the Araqua river confirmed the triploidy and showed that the macro B-chromosome was entirely heterochromatic. Ag-NOR characterization showed two chromosomes involved in the nucleolar activity in both specimens. Some aspects related to the origin of triploid fishes are described.

Cytotaxonomy, heterochromatic polymorphism and natural triploidy of a species of Astyanax (Pisces, Characidae) endemic to the Iguaçu river basin

“…The identification of two identical chromosomes and one differentiated on the 18 th and 19 th triads of the triploid specimen (Figs. 4, 5) corroborated this hypothesis, which had been suggested for other fish species (Morelli et al, 1983;Almeida-Toledo et al, 1985;Giuliano-Caetano and Bertollo, 1990;Maistro et al, 1994). However, the alternative hypothesis, haploid egg x diploid sperm fertilization, could not be ruled out in the origin of the triploidy.…”

Occurrence of natural triploidy in Rhamdia quelen (Siluriformes, Heptapteridae)

“…AgNORs were detected in the terminal portion of the short arm of 3 submetacentric chromosomes of the triploid individual (Figure 2b), confirming triploidy and suggesting that there is no genetic inactivation of the triploid ribosomal cistrons, a hypothesis also supported by Maistro et al (1994), Fernandes-Matioli et al (1998), Borin et al (2002, Garcia et al (2003), and Molina et al (2007). CMA 3 fluorochrome staining produced fluorescent bands coincident with AgNORs, in the triploid as well as the diploid individuals (Figure 2c and d, respectively), showing that the DNA sequences of ribosomal genes are GC-base rich in both karyotypes.…”

“…The occurrence of triploidy has already been recorded for 16 species of fish belonging to different families, with greater frequency in some species of the genus Astyanax (Table 1 In Curimata modesta (Venere and Galetti Jr., 1985) and Astyanax scabripinnis (Fauaz et al, 1994;Maistro et al, 1994), triploidy was accompanied by supernumerary or B chromosomes. Triploidy in Characidium gomesi (Centofante et al, 2001) and in Leporinus cf.…”

Comparative cytogenetics among sympatric species of Characidium (Pisces, Characiformes). Diversity analysis with the description of a ZW sex chromosome system and natural triploidy

“…al. 1985) and in Astyanax scabripinnis (FAUAZ et al 1994;MAISTRO et al 1994) triploidy is accompanied by supernumerary B chromosomes. The triploidy in C. gomesi becomes also interesting due to the sex chromosome system that occur in this species.…”