Research Article |
Corresponding author: Ana Lúcia Dias ( anadias@uel.br ) Academic editor: Inna Kuznetsova
© 2016 Tatiane Ramos Sampaio, Larissa Bettin Pires, Natalia Bortolazzi Venturelli, Mariana Campaner Usso, Renata da Rosa, Ana Lúcia Dias.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Sampaio TR, Pires LB, Venturelli NB, Usso MC, Rosa R, Dias AL (2016) Evolutionary trends in the family Curimatidae (Characiformes): inferences from chromosome banding. Comparative Cytogenetics 10(1): 77-95. https://doi.org/10.3897/CompCytogen.v10i1.6316
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The family Curimatidae is a fish group usually considered chromosomally conserved in their diploid number. However, some studies show small changes in the karyotype microstructure, and the presence of B chromosomes, indicating a chromosomal diversification within the group, even if structural changes in the karyotypes are not visible. Few studies associate this trait with an evolutionary pattern within the family. This study aimed to characterize the karyotype, nucleolus organizer regions (NORs), and heterochromatin distribution of six species of Curimatidae of the genera Cyphocharax Fowler, 1906 and Steindachnerina Fowler, 1906: C. voga (Hensel, 1870), C. spilotus (Vari, 1987), C. saladensis (Meinken, 1933), C. modestus (Fernández-Yépez, 1948), S. biornata (Braga et Azpelicueta, 1987) and S. insculpta (Fernández-Yépez, 1948) and contribute data to a better understanding of the mechanisms involved in the chromosomal evolution of this group of fish. All specimens had 2n=54, m-sm, and B microchromosomes. Five species exhibited single NORs, except for S. biornata, which showed a multiple pattern of ribosomal sites. NORs were chromomycin A3 positive (CMA3+) and 4’-6-diamino-2-phenylindole (DAPI-) negative, exhibiting differences in the pair and chromosomal location of each individual of the species. FISH with 5S rDNA probe revealed sites in the pericentrometic position of a pair of chromosomes of five species. However, another site was detected on a metacentric chromosome of C. spilotus. Heterochromatin distributed both in the pericentromeric and some terminal regions was revealed to be CMA3+/DAPI-. These data associated with the previously existing ones confirm that, although Curimatidae have a very conservative karyotype macrostructure, NORs and heterochromatin variability are caused by mechanisms of chromosome alterations, such as translocations and/or inversions, leading to the evolution and diversification of this group of fish.
Fluorochromes, heterochromatin, karyotype evolution, pisces, rDNA
Cytogenetic studies in Neotropical fish reveal great chromosome diversity with both intra- and interspecific karyotype variability. Within the order Characiformes, there are two distinct trends: groups that show a significant difference in diploid number and/or karyotype formulae and karyotypically homogeneous groups (
Small changes in the karyotype microstructure involving the nucleolus organizer regions (NORs) and heterochromatin distribution pattern occur as a result of chromosomal evolution. Such alterations can be regarded as relevant cytogenetic markers. Consequently, despite being considered conserved, some species of this group present exceptions to the observed regularity, allowing inferences about the evolutionary pathways within the family (
Another feature considered a chromosomal diversification within Curimatidae is the presence of B chromosomes in some species (
Although a number of cytogenetic studies show conservation of the diploid number (2n=54) in the family Curimatidae, divergence of nucleolus organizer regions and C-banding was observed. Nevertheless, few studies correlate the cytogenetic characteristics to the evolutionary trends within the family. Thus, this study aimed to characterize the karyotype, nucleolus organizer regions (NORs), and heterochromatin distribution of six species of Curimatidae of the genera Cyphocharax Fowler, 1906 and Steindachnerina Fowler, 1906, as well as contribute to a better understanding of the mechanisms underlying the chromosomal evolution of this interesting group of fish.
Six species of the family Curimatidae were analysed: Cyphocharax voga, C. spilotus, C. saladensis, C. modestus, Steindachnerina biornata and S. insculpta, collected from the Laguna dos Patos Hydrographic System/RS, Tramandaí River basin/RS, and Paranapanema River basin/SP/PR (Table
Species | Number of individuals | Collection sites | Hydrographic basin |
---|---|---|---|
Cyphocharax modestus | 5♀, 6♂ | Três Bocas stream, Londrina, PR, Brazil S 23°17'12.9" W 51°13'58.2" |
Paranapanema river |
Cyphocharax saladensis | 1♀, 9♂ | Agronomic Experiment Station of UFRGS’s Dam, Eldorado do Sul, RS, Brazil S 30°05'33.7" W 51°40'40.0" |
Laguna dos Patos hydrographic system |
Cyphocharax spilotus | 2♀, 2♂ | Capivara stream, Barra do Ribeiro, RS, Brazil S 30°17'34.0" W 51°19'21.2" |
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1♂ | Gasômetro, Porto Alegre, RS, Brazil S 30°02'06.3" W 51°14'29.12" |
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Cyphocharax voga | 1♀, 1♂ | Saco da Alemoa river, Eldorado do Sul, RS, Brazil S 29°59'15.6" W 51°14'24.1" | |
3♀, 9♂ | Capivara stream, Barra do Ribeiro, RS, Brazil S 30°17'34.0" W 51°19'21.2" |
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1♀, 3♂ | Gasômetro, Porto Alegre, RS, Brazil S 30°02'06.3" W 51°14'29.12" |
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5♂ | Barros lagoon, Osório, RS, Brazil S 29°56'30.0" W 50°19'32.0" |
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3♀, 4♂ | Quadros lagoon – Barra do João Pedro, Maquiné, RS, Brazil S 29°46'21.2" W 50°05'08.0" |
Tramandaí river | |
Steindachnerina biornata | 1♀, 1♂ | Forquetinha river, Canudos do Vale, RS, Brazil S 29°24'22.4" W 52°03'19.2" |
Laguna dos Patos hydrographic system |
Steindachnerina insculpta | 3♀, 2♂ | Três Bocas stream, Londrina, PR, Brazil S 23°17'12.9" W 51°13'58.2" |
Paranapanema river |
2♂ | Pavão stream, Sertanópolis, PR, Brazil | ||
6♀, 12♂ | Jacutinga river, Londrina, PR, Brazil S 23°23'6.6" W 51°04'35.8" |
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3♀, 7♂ | Água dos Patos river, Iepê, SP, Brazil S 23°12'23.3" W 50°56'49.1" |
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Total of individuals: | 93 |
Mitosis was stimulated by injecting animals with a yeast suspension (
The distribution of heterochromatin was analyzed by C-banding (
Fluorescence
All species analyzed showed 54 meta-submetacentric chromosomes (m-sm) and fundamental number (FN) equal to 108. All populations presented individuals with B microchromosomes of a dot type in all somatic cells (Figs
Karyotypes with B microchromosome of: a Cyphocharax modestus b Cyphocharax saladensis c Cyphocharax spilotus, showing AgNORs, CMA3 and 18S rDNA sites of each species. Note the secondary constrictions in square box (c). Bar: 5 µm.
Karyotypes with B microchromosome of: a Cyphocharax voga b Steindachnerina biornata c Steindachnerina insculpta, showing AgNORs, CMA3 and 18S rDNA sites of each species. Note the secondary constrictions in square box (a, b). Bar: 5 µm
One AgNOR was observed in the terminal region of a pair of chromosomes in all species (Figs
Chromosome pairs and positions of the nucleolus organizer regions (AgNORs).
Species | AgNOR pair | AgNOR position on chromosome | Secondary constriction |
---|---|---|---|
Cyphocharax modestus | 02 | Terminal/long arm | ------ |
Cyphocharax saladensis | 08 | Terminal/long arm | ------ |
Cyphocharax spilotus | 02 | Terminal/long arm | Interstitial/short arm |
Cyphocharax voga | 05 | Terminal/long arm | Terminal/long arm |
Steindachnerina biornata | 03 | Terminal/long arm | Terminal/long arm |
Steindachnerina insculpta | 12 | Terminal/short arm | ------ |
The AgNORs in the species Cyphocharax modestus, C. saladensis, C. spilotus, C. voga, and Steindachnerina insculpta were confirmed by fluorescence in situ hybridization (FISH) using an 18S rDNA probe (Figs
Two individuals of Cyphocharax voga collected in the Lagoa dos Barros/RS showed a block corresponding to the AgNOR and the CMA3 fluorochrome on the secondary constriction of a chromosome. FISH revealed two chromosomes with terminal 18S rDNA sites. One of the sites was larger than the other, revealing heteromorphism of this region (Fig.
Metaphases of Cyphocharax voga (Barros lagoon/RS): a Giemsa bAgNOR (sequential) c CMA3d 18S rDNA FISH. The arrows indicate the chromosome carrying the secondary constriction and AgNOR. Bar: 5 µm.
FISH with a 5S rDNA probe revealed sites in the pericentromeric position of a pair of metacentric chromosomes of five species: Cyphocharax spilotus, Cyphocharax voga, Steindachnerina insculpta, Cyphocharax modestus and Cyphocharax saladensis. Furthermore, another site was detected on a smaller metacentric chromosome of Cyphocharax spilotus (Fig.
5S rDNA FISH of: a Cyphocharax spilotus b Cyphocharax voga c Steindachnerina insculpta d Cyphocharax modestus e Cyphocharax saladensis. Note in (a) the presence of a small chromosome of C. spilotus with 5S rDNA sites (arrowhead). Bar: 5 µm.
Heterochromatin in Curimatidae species was preferentially observed in the pericentromeric and some terminal regions (Fig.
Metaphases with C-banding of: a Cyphocharax modestus b Cyphocharax saladensis c Cyphocharax spilotus d Cyphocharax voga e Steindachnerina biornata f Steindachnerina insculpta. Arrows and square box in (a), (b) and (f) highlight the heterochromatic B microchromosome. Note in (e) the pair of S. biornata with terminal heterochromatic regions on the long and short arm. Bar: 5 µm.
Metaphases with C-banding staining with CMA3 of: (a) Cyphocharax modestus; (b) Cyphocharax saladensis; (c) Cyphocharax spilotus; (d) Cyphocharax voga; (e) Steindachnerina biornata; (f) Steindachnerina insculpta. The (*) indicates the NOR pairs. Note in (b) the heterochromatic CMA3+ B microchromosome of C. saladensis (arrow and square box) and in (e) the heterochromatic pair of S. biornata (arrowhead). Bar: 5 µm.
Microchromosome B proved to be heterochromatic in Cyphocharax modestus, C. saladensis, and Steindachnerina insculpta (Figures
This study showed the first chromosome banding data for populations of Curimatidae of the Lagoa dos Patos and Tramandaí River basins, in the state of Rio Grande do Sul, as well as the first data on the species Cyphocharax saladensis and Steindachnerina biornata. All species maintained the pattern, presenting 2n = 54 m-sm. The model proposed by
Chromosome studies in the family Curimatidae. 2n, diploid number; FN, fundamental number; m, metacentric; sm, submetacentric; st, subtelocentric; a, acrocentric; B, supernumerary chromosome; term., terminal; peric., pericentromeric; centr., centromeric; inters., interstitial.
Species | Locality | 2n | Karyotypic formula | FN | AgNOR pair | Position | Number of cistrons 18S rDNA | Number/position of cistrons 5S rDNA | C banding | Reference |
---|---|---|---|---|---|---|---|---|---|---|
Curimata cyprinoides | Negro and Solimões river/AM | 54 | 44m + 10sm | 108 | 3 | term. long arm | - | - | - | 3 |
Araguaia river/MT | 54 | 44m + 10sm | 108 | 7 | term. long arm | - | - | - | 16 | |
Curimata inornata | Negro and Solimões river/AM | 54 | 40m + 14sm | 108 | 21 | inters. short arm | - | - | - | 3 |
Araguaia river/MT | 54 | 40m + 14sm | 108 | 3, 22 | term. long arm | - | - | Peric./term. | 16 | |
Curimata kneri | Negro and Solimões river/AM | 54 | 40m + 14sm | 108 | 27 | term. short arm | - | - | - | 3 |
Curimata ocellata | Negro and Solimões river/AM | 56 | 40m + 16sm | 112 | 26 | inters. short arm | - | - | - | 3 |
Curimata vittata | Negro and Solimões river/AM | 54 | 42m + 12sm | 108 | 9 | term. long arm | - | - | - | 3 |
Curimatella alburna | Negro and Solimões river/AM | 54 | 46m + 8sm | 108 | 14 | term. long arm | - | - | - | 3 |
Curimatella dorsalis | Miranda river/MS | 54 | 46m + 8sm | 108 | 13 | term. short arm | - | - | Peric. | 7 |
Paraná river/AR | 54 | 54m/sm | 108 | 2 | term. long arm | - | - | Centr./term. | 11 | |
Curimatella imaculata | Araguaia river/GO | 54 | 46m + 8sm | 108 | 24 | inters. long arm | - | - | Peric. | 16 |
Curimatella lepidura | São Francisco river/SP | 54 | 54m/sm | 108 | 9 | term. short arm | - | - | - | 2 |
Curimatella meyeri | Negro and Solimões river/AM | 54 | 46m + 8sm | 108 | 9 | term. long arm | - | - | - | 3 |
Curimatopsis myersi | Miranda river/MS | 46 | 42m + 4sm | 92 | - | - | - | - | - | 7 |
Cyphocharax gilbert | Paraibuna river/SP | 54 | 44m + 10sm | 108 | 2 | term. short arm | - | - | Peric./term. | 16 |
Cyphocharax cf. gillii | Bento Gomes river/MT | 54 | 54m/sm | 108 | 1 | inters. long arm | - | - | - | 2 |
Cyphocharax gouldingi | Araguaia river/GO | 54 | 54m + B | 108 | 2 | term. long arm | - | - | Peric. | 16 |
Cyphocharax modestus | Tiête river/SP | 54 | 54m/sm/B | 108 | - | term. long arm | - | - | Centr./term. | 1 |
Águas de São Pedro/SP | 54 | 54m/sm | 108 | 2 | term. long arm | - | - | - | 2 | |
Três Bocas stream/PR | 54 | 54m/sm + B | 108 | 2 | term. long arm | 2 | - | Peric./term. | 6, 13, 15, 18, 19 | |
Mogi-Guaçu river/SP | 54 | 54m/sm + B | 108 | - | - | - | - | Peric. | 8 | |
Taquari river/PR | 54 | 54m/sm + B | 108 | 2 | term. long arm | 2 | - | Peric./term. | 13, 15 | |
Tibagi river/PR | 54 | 54m/sm | 108 | 2 | term. long arm | 2 | - | - | 15 | |
Água da Floresta river/PR | 54 | 54m/sm | 108 | 2 | term. long arm | 2 | - | - | 15 | |
Paranapanema river/SP | 54 | 54m/sm + B | 108 | 2 | term. long arm | 2 | 4/peric. short arm | Centr./term. | 12, 14, 17 | |
Tietê river/SP | 54 | 54m/sm | 108 | 2 | term. long arm | 2 | 4/peric. short arm | Centr./term. | 12, 14, 17 | |
Cyphocharax nagelii | Mogi-Guaçu river/SP | 54 | 54m/sm | 108 | 25 | term. short arm | - | - | - | 2 |
Mogi-Guaçu river/SP | 54 | 46m + 8sm | 108 | 1, 2, 6, 11, 21 | term. long /short arm | - | - | Peric./term. | 16 | |
Cyphocharax platanus | Paraná river/AR | 58 | 52m/sm + 6st | 116 | 5 | term. short arm | - | - | Centr. | 11 |
Pirá-Pytá stream/ AR | 58 | 48m + 4 sm + 6st | 116 | 6 | term. short arm | - | - | Peric./term. | 16 | |
Cyphocharax cf. spilurus | Madeira river/RO | 54 | 54m/sm | 108 | 10 | term. long arm | - | - | - | 2 |
Cyphocharax spilotus | Paraná river/AR | 54 | 54m/sm + B | 108 | 1 | inters. long arm | - | - | Centr./term. | 10, 11 |
Capivara stream/RS | 54 | 54m/sm + B | 108 | 2 | term. long arm | 2 | - | Peric./term. | 18, 19 | |
Gasômetro/RS | 54 | 54m/sm + B | 108 | 2 | term. long arm | 2 | 3/peric. short arm | Peric./term. | 18, 19 | |
Cyphocharax vanderi | Preto river/SP | 54 | 54m/sm | 108 | 6 | term. long arm | - | - | - | 2 |
Cyphocharax voga | Bolacha stream/RS | 54 | 54m/sm | 108 | 6 | term. long arm | - | - | - | 2 |
Paraná river/AR | 54 | 54m/sm | 108 | - | term. long arm | - | - | Inters./term. | 11 | |
Saco da Alemoa river/RS | 54 | 54m/sm + B | 108 | 5 | term. long arm | 2 | - | Peric./term. | 18, 19 | |
Capivara stream/RS | 54 | 54m/sm + B | 108 | 5 | term. long arm | 2 | - | Peric./term. | 18, 19 | |
Gasômetro/RS | 54 | 54m/sm + B | 108 | 5 | term. long arm | 2 | - | Peric./term. | 18, 19 | |
Barros lagoon/RS | 54 | 54m/sm + B | 108 | 5 | term. long arm | 2 | 2/peric. short arm | Peric./term. | 18, 19 | |
Quadros lagoon/RS | 54 | 54m/sm + B | 108 | 5 | term. long arm | 2 | - | Peric./term. | 18, 19 | |
Cyphocharax saladensis | A.E.S UFRGS dam/RS | 54 | 54m/sm + B | 108 | 8 | term. long arm | 2 | 2/peric. short arm | Peric./term. | 18, 19 |
Potamorhina altamazonica | Negro and Solimões river/AM | 102 | 2m + 2sm + 98a | 106 | 5 | term. long arm | - | - | Peric./inters/term. | 4 |
Potamorhina latior | Negro and Solimões river/AM | 56 | 52m + 2sm + 2st | 112 | 25 | term. long arm | - | - | Peric./term. | 4 |
Potamorhina pristigaster | Negro and Solimões river/AM | 54 | 42m + 12sm | 108 | 25 | term. short arm | - | - | Peric. | 4 |
Potamorhina squamoralevis | Paraná river/AR | 102 | 14m/sm + 88a | 116 | - | term. long arm | - | - | Centr. | 11 |
Psectrogaster amazonica | Araguaia river/MT | 54 | 44m + 10sm | 108 | 17 | term. short arm | - | - | Peric. | 16 |
Psectrogaster curviventris | Miranda river/MS | 54 | 42m + 12sm | 108 | 20 | term. short arm | - | - | Peric. | 7 |
Paraná river/AR | 54 | 54m/sm | 108 | - | inters. long arm | - | - | Centr./term. | 11 | |
Psectrogaster rutiloides | Negro and Solimões river/AM | 54 | 42m + 12sm | 108 | 9 | term. long arm | - | - | - | 3 |
Steindachnerina amazonica | Araguaia river/GO | 54 | 42m + 12sm | 108 | 2, 23 | term. long arm | - | - | Peric./term. | 16 |
Steindachnerina biornata | Forquetinha river/RS | 54 | 54m/sm + B | 108 | 3 | term. long arm | 4 | - | Peric./term. | 18, 19 |
Steindachnerina brevipinna | Miranda river/MS | 54 | 48m + 6sm | 108 | 17 | term. short arm | - | - | Centr./term. | 7 |
Paraná river/AR | 54 | 54m/sm | 108 | 15 | term. long arm | - | - | Centr./inters./term. | 11 | |
Steindachnerina conspersa | Paraguai river/MS | 54 | 54m/sm | 108 | 2 | inters. long arm | - | - | - | 2 |
Paraná river/AR | 54 | 54m/sm | 108 | 2 | term. long arm | - | - | Centr./inters/term. | 11 | |
Steindachnerina elegans | São Francisco river/SP | 54 | 54m/sm | 108 | 25 | term. short arm | - | - | - | 2 |
Steindachnerina gracilis | Araguaia river/MT | 54 | 38m + 16sm | 108 | - | term. long arm | - | - | Peric. | 16 |
Steindachnerina cf. guentheri | São Francisco river/AC | 54 | 54m/sm | 108 | 24 | term. short arm | - | - | Peric./inters/term. | 9 |
Steindachnerina insculpta | Mogi-Guaçu river/SP | 54 | 54m/sm | 108 | 25 | term. short arm | - | - | - | 2 |
Passa-Cinco river/SP | 54 | 54m/sm | 108 | 25 | term. short arm | - | - | - | 2 | |
Paranapanema river/SP | 54 | 54m/sm + B | 108 | - | - | - | - | Peric. | 5 | |
Reserva Jurumirim/SP | 54 | 54m/sm + B | 108 | - | - | - | - | Peric. | 5 | |
Paranapanema river/SP | 54 | 54m/sm | 108 | 7 | term. short arm | 2 | 2/peric. short arm | Centr./term. | 12, 14, 17 | |
Tietê river/SP | 54 | 54m/sm | 108 | 7 | term. short arm | 2 | 2/peric. short arm | Centr./term. | 12, 14, 17 | |
Três Bocas stream/PR | 54 | 54m/sm + B | 108 | 7 | term. short arm | 2 | - | Peric./term. | 13, 15 | |
Taquari river/PR | 54 | 54m/sm | 108 | 7 | term. short arm | 2 | - | Peric./term. | 13, 15 | |
Tibagi river/PR | 54 | 54m/sm | 108 | 7 | term. short arm | 2 | - | Peric./term. | 13, 15 | |
Água da Floresta river/PR | 54 | 54m/sm | 108 | 7 | term. short arm | 2 | - | Peric./term. | 13, 15 | |
Cachoeira de Emas/SP | 54 | 54m/sm | 108 | 22 | term. short arm | - | - | Peric./term. | 16 | |
Água dos Patos river/SP | 54 | 54m/sm + B | 108 | 12 | term. short arm | 2 | - | Peric./term. | 18, 19 | |
Três Bocas streams/PR | 54 | 54m/sm + B | 108 | 12 | term. short arm | 2 | 2/peric. short arm | Peric./term. | 18, 19 | |
Pavão stream/PR | 54 | 54m/sm + B | 108 | 12 | term. short arm | 2 | - | Peric./term. | 18, 19 | |
Jacutinga river/PR | 54 | 54m/sm + B | 108 | 12 | term. short arm | 2 | - | Peric./term. | 18, 19 | |
Steindachnerina leucisca | Negro and Solimões river/AM | 54 | 48m + 6sm | 108 | 15 | term. short arm | - | - | - | 3 |
Besides the presence of B chromosomes, another striking feature of the Curimatidae species are the nucleolus organizer regions. Previous works have described the AgNORs of Cyphocharax spilotus and Steindachnerina insculpta on other pairs besides those observed here (Table
All studied populations of Cyphocharax modestus presented the AgNOR on pair 2. The populations of C. voga presented the AgNOR mainly on pair 5 (Table
In many fish groups, including Curimatidae, there is a high correlation between AgNORs and secondary constriction (
The results of FISH in Steindachnerina biornata showed another species with multiple NOR patterns among Curimatidae. The above method revealed an unusual feature, which was observed only in Curimata inornata Vari, 1989, Cyphocharax nagelii (Steindachner, 1881), Steindachnerina amazonica (Steindachner, 1911), and S. gracilis Vari & Vari, 1989 (
The existing literature presents scarce data on fluorochrome staining in the family Curimatidae, with reports only in Cyphocharax modestus and Steindachnerina insculpta (
NOR heteromorphism in the homologous chromosomes of two individuals of Cyphocharax voga from the population of the Lagoa dos Barros/RS may be attributable to unequal crossing over, where the small site may have become inactive, or could not be detected by silver nitrate or CMA3 because of their size.
FISH with the 5S rDNA probe revealed results coincident with those found by
To explain the presence of larger and smaller 5S rDNA sites,
C-banding analyses did not allow us to characterize and differentiate among the species and/or genera analyzed in this study. However,
The difference in the amount of heterochromatin in Curimatidae reflects the interpopulation variability occurring within this family. It is believed that the amount of heterochromatin can play a significant role in the chromosome evolution in this fish group. As previously mentioned, Curimatidae can be established in isolated populations under different environmental conditions. Such conditions may enable increased variations in the distribution of heterochromatin.
CMA3 fluorochrome staining revealed fluorescent signals in the heterochromatic regions of many chromosomes of the complement, showing that heterochromatin in these species consists mostly of GC base pairs. A chromosomal pair detected in Steindachnerina biornata can be considered a species-specific marker, since we evidenced heterochromatin in the two terminal regions of the NOR-bearing pair, i.e., a block on the long arm associated with the NOR and a more discreet marking on the short arm. The NOR adjacent to the heterochromatic blocks may facilitate chromosome breakage, leading to structural rearrangements in these regions (
In Cyphocharax modestus, C. saladensis, and Steindachnerina insculpta, the B microchromosome presented itself entirely heterochromatic, indicating the total absence of gene activity, as in other studied populations of C. modestus (
Two hypotheses have been proposed for the origin of B chromosomes in Curimatidae (
In conclusion, these data associated with the previously existing studies for the group, show that, although Curimatidae have a very conservative karyotype macrostructure, the interpopulation variation in NOR locations and distribution of heterochromatin are caused by important mechanisms of chromosome alterations, such as translocations and/or inversions, leading to the evolution and diversification of this group of fish.
The authors are grateful to Dra. Lucia Giuliano-Caetano and MSc Juceli Gonzalez Gouveia for the collection of fish samples. This research was supported by a grant from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and received permission from Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis (IBAMA) to collect fish specimens.