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

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. Seis espécies de Serrasalmidae da Amazônia central, representantes dos gêneros Serrasalmus (S. elongatus, S. maculatus, S. cf. rhombeus e S. rhombeus ), Pygocentrus (P. nattereri)e Colossoma (C. macropomum), foram analisadas quanto à distribuição das Ag-RONs, heterocromatina C-positiva e dos genes de RNAr 18S e 5S nos cromossomos. Todos os espécimes apresentaram 2n = 60 cromossomos, exceto S. cf. rhombeus, com 2n = 58, e C. macropomum com 2n = 54 cromossomos. As Ag-RONs foram múltiplas e localizadas nos braços curtos de cromossomos subtelo-acrocêntricos em todas as espécies de Serrasalmus e em P. nattereri, mas foram encontrados em cromossomos metacêntricos em C. macropomum. Os sítios de DNAr 18S, foram geralmente coincidentes com as Ag-RONs, embora algumas espécies tenham apresentado um maior número e/ou uma localização distinta desses sítios. A heterocromatina C-positiva foi preferencialmente encontrada como uma conspícua banda proximal no par metacêntrico número 7 em todas as espécies de Serrasalmus e número 3 em P. nattereri. Os sítios de DNAr 5S foram detectados em um único par cromossômico nas seis espécies sendo que nas espécies de Serrasalmus, este par foi o de número 7 e em P. nattereri o de número 3, colocalizados com bandas heterocromáticas conspícuas. No entanto, em C. macropomum, apenas um homólogo (provavelmente pertencente ao par número 12) apresentou sítios ...

Chromosome mapping of repetitive sequences in four Serrasalmidae species (Characiformes)

“…Fluorescence in situ hybridization with 18S rDNA sequences showed multiple signals in two species, as previously reported for other Serrasalmidae (Nakayama et al , 2008, 2012). The 18S rDNA distribution in three chromosome pairs of C. macropomum corroborated earlier findings for that same species (Nirchio et al , 2003; Nakayama et al , 2012), in contrast to the Ag-NOR staining that evidenced only two pairs.…”

“…This kind of rearrangements have been reported for a number of other fish species (Garcia and Moreira-Filho, 2005; Mazzuchelli et al , 2007; Nakayama et al , 2008, 2012; Schneider et al , 2012). Besides having 2n = 54 as its exclusive diploid number, the “pacus” clade is the only one whose species consistently present only biarmed chromosomes (metacentric, submetacentric, and subtelocentric).…”

“…INPA/UFAM, Manaus, AM) (García-Parra WJ, 2000, PhD Thesis. INPA/UFAM, Manaus, AM), and the “piranhas” clade, considered the most derived, presenting diploid numbers that vary from 58 to 64 and the presence of acrocentric pairs (Muramoto et al , 1968; Nakayama et al , 2002, 2008, 2012). This scenario suggests an evolutionary trend towards increasing chromosome numbers mainly due to chromosomal fissions.…”

“…“Pacus” are considered basal and “piranhas” are thought to be the most derived clade. Supporting this classification, cytogenetic studies have demonstrated variations in the diploid numbers in the family, with 2n = 54 for the “pacus” clade (Nirchio et al , 2003; Nakayama et al , 2012), 2n = 58 for the Myleus clade (Porto JIR, 1999, PhD Thesis. INPA/UFAM, Manaus, AM) (García-Parra WJ, 2000, PhD Thesis.…”

“…INPA/UFAM, Manaus, AM), and 2n = 58 to 64 for the most derived “piranhas” clade (Muramoto et al , 1968; Nakayama et al , 2001). Although the karyotypes of many species of this family have been described (Almeida-Toledo et al , 1987; Cestari and Galetti Jr, 1992a,b; Nakayama et al , 2000, 2001, 2002, 2008, 2012; Centofante et al , 2002; Nirchio et al , 2003; Gaviria et al , 2005) (García-Parra WJ, 2000, PhD Thesis. INPA/UFAM, Manaus, AM), analyses using molecular cytogenetic techniques, mainly in the most basal genera ( Colossoma , Mylossoma and Piaractus ), are still scarce.…”