Chromosome divergence and NOR polymorphism in Bryconamericus aff. iheringii (Teleostei, Characidae) in the hydrographic systems of the Paranapanema and Ivaí Rivers, Paraná, Brazil

Abstract

Cytogenetic studies were carried out in three populations of Bryconamericus aff. iheringii from two hydrographic systems of the Paranapanema and Ivaí Rivers, separated by a watershed, both belonging to the upper Paraná River basin. Specimens had a constant diploid number 2n = 52 chromosomes. However, three karyotype formulae were identified in the three populations: B. aff. iheringii from the Maringá stream had 12M+18SM+8ST+14A (FN = 90); specimens from Keller River showed 8M+28SM+6ST+10A (FN = 94) and specimens from the Tatupeba stream had 8M+20SM+8ST+16A (FN = 88). Nucleolar organizer regions (NORs) were identified by silver nitrate staining and fluorescent in situ hybridization (FISH) with an 18S rDNA probe. Specimens from Tatupeba stream had a simple NOR system located in a terminal position of the short arm of a pair of large submetacentric chromosomes. Ag-NOR and FISH methodologies revealed multiple NORs in specimens of the Maringá stream and Keller River. Differences in chromosome structure and in NOR patterns in the three populations of B. aff. iheringii revealed fixed evolutionary chromosome divergence. Aspects related to karyotypic variations and to geographic isolation of these populations are discussed.

Occurrence of Cytotypes and Variability of AgNORs in a Population of <i>Bryconamericus</i> aff. <i>iheringii</i> (Characidae)

“…However, the single NOR system has been observed in 3 populations of B. aff. iheringii (Paintner-Marques et al 2003;Capistano et al 2008 and through the present study). According to Galetti Jr. (1998) having a single pair of chromosomes bearing 45S rDNA is considered a primitive character for fish.…”

“…iheringii from the Três Bocas Stream also showed the same chromosomal NOR variations. Capistano et al (2008) also observed a number variation from 2-4 AgNOR chromosomes, both inter and intra-individual with markings in the region of the short and/or on the long arm in Bryconamericus aff. iheringii collected in the Maringá Stream (cytotype I) and in the Keller River (cytotype II), indicating a system of multiple NORs for these 2 populations.…”

“…However, simple NORs have already been found in 2 populations of B. aff. iheringii Boulenger, 1887 by Paintner-Marques et al (2003) and Capistano et al (2008), and recently, Santos et al (2012) have observed single and multiple NORs in the same population of Bryconamericus ecai.…”

“…E, analyzed by Wasko and Galetti Jr (1998), presents a different diploid number, 2n=54 and the variations in the karyotypic structure of this group of fish are significant, as listed in Table 1. The nucleolus organizer regions (NORs) are also quite variable in this genus, and may present intra-and intervariations in the number and location of ribosomal DNA cistrons, thus featuring Bryconamericus as a group with multiple NORs (Wasko et al 1996, Wasko and Galetti Jr. 1999, Paintner-Marques et al 2002a, Capistano et al 2008, Santos et al 2012. However, simple NORs have already been found in 2 populations of B. aff.…”

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

“…As occur with C-bands, the genus Astyanax also shows distinct patterns in relation to NORs, with single and multiple systems and with both intra-and inter-specific variations in number and locations on the chromosomes (Kavalco and Moreira-Filho, 2003;Pazza et al, 2006;Capistano et al, 2008;Kavalco et al, 2011). In this study a multiple marking system was only found in Astyanax aff.…”