Karyotype differentiation and cytotaxonomic considerations in species of Serrasalmidae (Characiformes) from the Amazon basin

Celeste Mutuko Nakayama,Eliana Feldberg,Luiz Antonio Carlos Bertollo

doi:10.1590/s1679-62252012000100005

Celeste Mutuko Nakayama, Eliana Feldberg + Show 1 more

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https://doi.org/10.1590/s1679-62252012000100005

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Abstract

Six species of Serrasalmidae from the central Amazon, representatives of the genera Serrasalmus (S. elongatus, S. maculatus, S. cf. rhombeus, and S. rhombeus), Pygocentrus (P. nattereri), and Colossoma (C. macropomum), were analyzed regarding the distribution of the Ag-NORs, C-positive heterochromatin and 18S and 5S rRNA genes on the chromosomes. All specimens had 2n = 60 chromosomes, except S. cf. rhombeus, with 2n = 58, and C. macropomum with 2n = 54 chromosomes. The Ag-NORs were multiple and located on the short arms of subtelo-acrocentric chromosomes in all Serrasalmus species and in P. nattereri, but were found on metacentric chromosomes in C. macropomum. The 18S rDNA sites were usually coincident with Ag-NORs, although some species had a higher number and/or a distinct localization of these sites. C-positive heterochromatin was preferentially situated in centromeric regions, remarkably on metacentric pair number 7 in all Serrasalmus species and number 3 in P. nattereri, which beared a conspicuous proximal C-band on the long arms. The 5S rDNA sites were detected in a single chromosomal pair in all species. In Serrasalmus and P. nattereri, this pair was the number 7 and 3, respectively, thereby revealing its co-localization with the conspicuous heterochromatic band. However, in C. macropomum, only one homologue (probably belonging to pair number 12) exhibited 5S rDNA sites on the short arms, close to the centromere. The present data revealed reliable cytotaxonomic markers, enabling the evaluation of karyotype differentiation and interrelationships among Serrasalmidae, as well as the probable occurrence of a species complex in S. rhombeus.

Highlights

Chromosome banding techniques have been useful in evolutionary cytogenetics, as they allow the identification of potential chromosome markers related to karyotype interrelationships
The 18S rDNA sites coincided with Ag-nucleolar organizer regions (NORs) sites
Ag-NORs in Serrasalmidae have been analyzed since the 1980s and have invariably been visualized as multiple sites usually located in the terminal region on the short arms of subtelo-acrocentric chromosomes, some species bear terminal Ag-NORs on the long arms (Galetti Jr. et al, 1985; Almeida-Toledo et al, 1987; Cestari & Galetti Jr. 1992a, b; Martins-Santos et al, 1994; Nakayama et al, 2001, 2002; 2008; Centofante et al, 2002a; Nirchio et al, 2003; Gaviria et al, 2005)

Summary

Introduction

Chromosome banding techniques have been useful in evolutionary cytogenetics, as they allow the identification of potential chromosome markers related to karyotype interrelationships. The detection of nucleolar organizer regions (NORs) by silver nitrate staining (Ag-NORs) has been one of the most widely employed procedures in fish, especially from 1980s on, providing important information for cytotaxonomic and evolutionary studies (Galetti Jr. et al, 1984; Gold, 1984; Venere & Galetti Jr., 1989; Feldberg et al, 1992, 2003). Since the 1990s, chromosome studies have improved quickly due to the use of base-specific fluorochromes, such as chromomycin A and mithramycin, and the development of fluorescent in situ hybridization (FISH).

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