Cytogenetic analyses of two Curimatidae species (Pisces; Characiformes) from the Paranapanema and Tietê Rivers

Abstract

Cytogenetic analyses were performed in two Curimatidae species (Steindachnerina insculpta and Cyphocharax modesta) from the Paranapanema and Tietê Rivers (São Paulo State, Brazil), showing a karyotype composed of 54 meta-submetacentric chromosomes in both species. Silver-and chromomycyn-staining and fluorescent in situ hybridization (FISH) using a 18S rDNA probe indicated that the nucleolar organizer regions (NORs) of both species are localized in the terminal region of the long arm of two metacentric chromosomes. Although a single NOR system was evidenced in both analyzed species, S. insculpta and C. modesta presented the nucleolar organizer regions in distinct chromosome pairs, indicating that these cistrons can be considered cytogenetic markers. Variation on the amount and distribution of the constitutive heterochromatin (C-bands) could also be detected between the two species -while S. insculpta presented few heterochromatic blocks, intensely stained C-bands were evidenced in C. modesta specially in the terminal region of the long arm of the NOR-bearing chromosomes. Although most Curimatidae species have been characterized by homogeneous karyotypes, isolated populations could be established under different environmental conditions leading to karyotype micro-structure variations specially related to the NORs localization and C-banding distribution. The obtained data were useful for the cytogenetic characterization and differentiation of S. insculpta and C. modesta and could be used in evolutionary inferences in the Curimatidae group.Keywords: constitutive heterochromatin, Cyphocharax modestus, fish, NOR, Steindachnerina insculpta. Análises citogenéticas de duas espécies de Curimatidae (Pisces; Characiformes) dos rios Paranapanema e Tietê ResumoAnálises citogenéticas foram realizadas em duas espécies de Curimatidae (Steindachnerina insculpta e Cyphocharax modestus) provenientes dos rios Paranapanema e Tietê (Estado de São Paulo, Brasil), evidenciando um cariótipo composto por 54 cromossomos meta-submetacêntricos em ambas as espécies. Coloração com nitrato de prata e cromomicina e hibridação in situ fluorescente (FISH), utilizando uma sonda de DNAr 18S, mostraram que as regiões organizadoras de nucléolos (RONs) de ambas as espécies estão localizadas na região terminal do braço longo de dois cromossomos metacêntricos. Embora as espécies analisadas tenham apresentado um sistema de RONs simples, S. insculpta e C. modesta apresentaram as regiões organizadoras de nucléolos em distintos pares de cromossomos, indicando que estes cístrons podem ser considerados marcadores citogenéticos. Variação na quantidade e distribuição de heterocromatina constitutiva (bandas C) também pôde ser detectada entre as duas espécies -enquanto S. insculpta apresentou poucos blocos heterocromáticos, bandas C intensamente coradas foram evidenciadas em C. modesta especialmente na região terminal do braço longo dos cromossomos portadores de RONs. Embora a maioria das espécies de Curimatidae seja caracterizada por cariótipos homogêneos...

Evolutionary trends in the family Curimatidae (Characiformes): inferences from chromosome banding

“…The existing literature presents scarce data on fluorochrome staining in the family Curimatidae, with reports only in Cyphocharax modestus and Steindachnerina insculpta (De Rosa et al 2007; Teribele et al 2008; Martins et al 1996) and the results are coincident with those observed in this study, indicating that NORs are rich in GC base pairs.…”

“…These fish occur in different ecosystems of the Neotropical region, and isolated populations can be established under different environmental conditions, enabling an increase in the frequency of certain variations (Brassesco et al 2004; Vari 2003). These variations may be ascribable to rearrangements of the chromosomal microstructure, such as translocations and/or inversions (Venere and Galetti Jr. 1989; De Rosa et al 2007). …”

“…The populations of Cyphocharax voga presented the AgNOR mainly on pair 5 (Table 3), indicating that these sites can be considered important species-specific cytogenetic markers (Venere et al 2008; De Rosa et al 2007). …”

Recent chromosome diversification in the evolutionary radiation of the freshwater fish family Curimatidae (Characiformes)

“…In addition, the presently available results for Ag‐NOR also show extensive variability among curimatids, indicating that this character is a good cytotaxonomic marker for several species. While C. inornata , S. amazonica , S. gracilis and C. nagelii present multiple chromosomes bearing NOR sites, other species show only one NOR‐bearing chromosome pair, as confirmed in some species with 18S rDNA FISH (fluorescence in situ hybridization) (De Rosa et al , 2007). In C. nagelii , individuals collected from two populations of the same major hydrographic system (Upper Paraná) showed Ag‐NOR divergence.…”

First cytogenetic analysis of Ichthyoelephas humeralis (Günther, 1860) by conventional and molecular methods with comments on the karyotypic evolution in Prochilodontidae

“…Data on NORs in Chilodontidae and Curimatidae show that species in these families have only one NOR-bearing chromosome pair, usually a large metacentric with NORs in the terminal position (Martins et al 2000, De Rosa et al 2006, Rodrigo et al 2008, Venere et al 2008, Arai 2011) as observed in Ichthyoelephas humeralis , subject of this study. FISH experiments with species of Curimatidae show that the 18S rDNA sites are coincident with the Ag-NORs, and 5S rDNA are found on different chromosomes in interstitial positions in all species analyzed (De Rosa 2006, 2007). …”