Corresponding author: P.C. Venere (
Academic editor: A. Maryańska-Nadachowska
Cichlids represent one of the most species-rich families of fishes and have attracted the attention of evolutionary biologists due to the rapid radiation occurring in some groups and the importance of some species in the world aquaculture. Cytogenetic analysis was conducted in 10 cichlid species from the Araguaia River, Amazon Basin, Brazil. The chromosome number was 2n=48 for all analyzed species except for
The family
The African and Neotropical cichlids,
The chromosome numbers of approximately 135 species of cichlids have been determined. Although more than 60% of the species present karyotypes with 2n=48, the diploid number ranges from 2n=32 to 2n=60 (
Synthesis of the cichlid species analyzed with respect to the karyotypic formulae, heterochromatin distribution and CMA3 patterns. m/sm, metacentric and submetacentric chromosomes; st/a, subtelocentric and acrocentric chromosomes; mi, microchromosomes; q, the long arm of a chromosome; p, the short arm of a chromosome; PeriC or C, pericentromeric regions; Prox, proximal portion of a chromosome; Term, Terminal portion of a chromosome; Int, interstitial portion of a chromosome; Adj, adjacent region; NOR, nucleolus organizing region; The numbers in the column “Additional blocks” indicate the number of chromosomes with the described pattern; in some cases, the ranking of these chromosomes are indicated in parentheses.
Tribes and species | Origin of animals | 2n | Karyotypic formulae | Heterochromatin distribution | CMA3 + blocks | References | |
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General pattern | Additional blocks | ||||||
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Das Mortes river, Araguaia basin, MT State, Brazil | 48 | 48st/a | PeriC | NOR; term 2 | NOR (term) | This work | |
Araguaia river, MT State, Brazil | 48 | 48st/a | C | NOR; int 1 q | absent |
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Uatumã and Solimões rivers, AM State, Brazil | 48 | 48a | PeriC | NOR; int 1 q | absent |
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Uatumã and Jaú rivers, AM State, Brazil | 48 | 48a | PeriC | NOR; int 1 q | absent |
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Das Mortes river, Araguaia basin, MT State, Brazil | 48 | 48st/a | PeriC | NOR; term 1 q | NOR (term) and PeriC | This work | |
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Tietê river, SP State, Brazil | 48 | 16m/sm + 32st/a | C | NOR | absent |
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Paraná river, Missiones, Argentina | 46 | 16m/sm + 30st/a | PeriC | absent | absent |
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Das Mortes river, Araguaia basin, MT State, Brazil | 48 | 4m/sm + 44st/a | PeriC | NOR; some prox blocks | NOR (int) | This work | |
Jupiá river, PR State, Brazil | 48 | 8m/sm + 40st/a | PeriC | NOR; 1 p almost completely heterochromatic (1st pair) | absent |
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Das Mortes river, Araguaia basin, MT State, Brazil | 48 | 6m/sm + 42st/a | PeriC | NOR; some prox blocks | NOR (term) and PeriC | This work | |
Negro and Solimões rivers, AM State, Brazil | 48 | 8m/sm + 40st/a | PeriC | NOR; term 1 q (19th pair) | absent |
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Negro and Solimões rivers, AM State, Brazil | 48 | 8m/sm + 40st/a | PeriC | adj NOR | absent |
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Iguaçu river, PR State, Brazil | 48 | 4m + 4sm + 14st + 26a | PeriC | Some term blocks | NOR |
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Negro and Solimões rives, AM State, Brazil | 48 | 6m/sm + 42st/a | PeriC | adj NOR | absent |
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São Gonçalo stream and Polegar lake, RS State, Brazil | 48 | 4m + 4sm + 40st/a | PeriC | term 1 p and 1 q (1st pair); int 1 q (1st pair) | NOR |
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Porto Rico region, Paraná river basin, PR State, Brazil | 48 | 2m + 4sm + 42st/a | PeriC | int 2 (1st and 5th pairs) | absent |
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Negro and Solimões rivers, AM State, Brazil | 48 | 8m/sm + 40st/a | PeriC | NOR; int 1 q (2nd pair) | absent |
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Paraná river, Missiones, Argentina | 48 | 6m/sm + 42st/a | PeriC | absent | absent |
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Negro and Solimões river, AM State, Brazil | 48 | 6m/sm + 42st/a | PeriC | adj NOR; int 1 q (10th pair) | absent |
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Iguaçu river, PR State, Brazil | 48 | 4m + 4sm + 14st + 26a | PeriC | Some term blocks | NOR |
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Iguaçu river, PR State, Brazil | 48 | 4m + 4sm + 14st + 26a | PeriC | Some term blocks | NOR |
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Socavão and Verde rivers, PR State, Brazil | 48 | 6sm + 42st/a | PeriC/C | absent | NOR |
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Jaguarriaíva river, PR State, Brazil | 48 | 6sm + 42st/a | PeriC/C | Some int blocks | NOR |
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Saco da Alemoa, Gasômero, RS State, Brazil | 48 | 4sm + 44st/a | PeriC | NOR | NOR |
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Cambezinho and Três Bocas stream, Tibagi river basin, PR State, Brazil | 48 | 4sm + 44st/a | C | NOR | NOR |
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Pirapo river, Paranapanema basin, PR State, Brazil | 48 | 8sm + 40st/a | PeriC | prox 1 p (10th pair) | absent |
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Das Mortes river, Araguaia basin, MT State, Brazil | 48 | 4m/sm + 44st/a | PeriC | NOR; 1 p almost completely heterochromatic | NOR (int) | This work | |
Paraná river, Missiones State, Argentina | 48 | 2m/sm + 46st/a | PeriC | absent | absent |
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Saco da Alemoa, Barra do Ribeiro, Gasômetro, RS State, Brazil | 48 | 4m + 44st/a; 6m + 42st/a | PeriC | NOR | NOR |
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Saco da Alemoa, Forqueta river, RS State, Brazil | 48 | 4m + 4sm + 40st/a | PeriC | absent | NOR |
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Paraná river, Missiones, Argentina | 48 | 2m/sm + 46st/a | PeriC | absent | absent |
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Das Mortes river, Araguaia basin, MT State, Brazil | 48 | 4m/sm + 44st/a | PeriC | absent | NOR | This work | |
Porto rico region, Parana river basin, PR State, Brazil | 48 | 6sm + 42st/a | PeriC | absent | absent |
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Araguaia river, MT State, Brazil | 48 | 12m/sm + 36st/a | PeriC | absent | NOR | This work | |
São Gonçalo stream and Polegar lake, RS State, Brazil | 48 | 22sm + 26st/a | PeriC/C | absent | NOR |
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Paraná river, Missiones, Argentina | 44 | 22m/sm + 8st/a + 14 mi | PeriC | NOR; p arm of 5th pair completely heterochromatic | absent |
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Paraná river, Missiones, Argentina | 48 | 8m/sm + 40st/a | PeriC | absent | absent |
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Tarumã lake, PR State, Brazil | 48 | 10sm + 38 st/a | PeriC/C | absent | NOR |
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Porto rico region, Parana river basin, PR State, Brazil | 48 | 20sm + 28 st/a | PeriC | prox 2 p (2nd and 9th pairs) | absent |
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Araguaia river, MT State, Brazil | 44 | 4m/sm + 40st/a | PeriC | absent | NOR | This work | |
Paraná river, PR State, Brazil | 43 | 5m + 38a | C | NOR | absent |
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44 | 4m + 40a | ||||||
45 | 3m + 42a | ||||||
46 | 2m + 44a | ||||||
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Araguaia river, MT State, Brazil | 48 | 8m/sm + 40st/a | PeriC | absent | NOR (term) and int 1 p | This work | |
Das Mortes river, Araguaia basin, MT State, Brazil | 48 | 14m/sm + 34st/a | PeriC | NOR; term 2 q | NOR (term) | This work | |
Jari river, PA State, Brazil | 48 | 12m/sm + 36st/a | PeriC/C | 1 p almost completely heterochromatic (1st pair) | NOR, some centromeres |
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Bauana lake, Tefé river, AM State, Brazil | 60 | 8m/sm + 8st/a +4mi; 50m/sm + 6st/a +4mi | PeriC | Some prox blocks; int 1 q (1st pair) | absent |
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Boi-boi stream, Negro river, AM State, Brazil | 60 | 50m/sm + 10st/a; 54m/sm + 6st/a | PeriC | Some prox blocks | absent |
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Manacapuru river, AM State, Brazil | 60 | 52m/sm + 4st/a +4mi | PeriC | Some prox blocks | absent |
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It was analyzed 10 South American cichlid species of the subfamily
Mitotic chromosome preparations were obtained from kidney cells according to
The chromosome structure was analyzed through silver nitrate staining, Chromomycin A3 (CMA3) staining and C-banding.
To detect nucleolus organizer regions (NORs), the silver staining of the chromosomes was performed according to
The constitutive heterochromatin was detected using saline solution according to
The CMA3 staining was conducted according to the method by
The chromosome spreads were analyzed using an Olympus BX 61 microscope, and the images were captured with the Olympus DP71 digital camera with the software Image-Pro MC 6.0. There were analyzed 30 metaphase spreads for all cytogenetic procedures performed for each animal sample. Karyotypes were arranged in the order of decreasing chromosome size, and the chromosomes were classified as either meta/submetacentrics (m/sm) or subtelo/acrocentrics (st/a).
All of the species analyzed have 2n=48 except
The results of C-banding revealed the heterochromatin generally restricted to pericentromeric regions. Additional blocks of heterochromatin were noticed in
Characteristic heterochromatic blocks corresponding to AgNOR bearing regions (two blocks, one in each homologue) were observed in all species, and these blocks were consistent with CMA3 positive (CMA3+) blocks (
Representative karyotypes of
Metaphases of several cichlid species under different chromosome treatments. The species are indicated on the left. The first, second and third columns show C-banded, AgNOR- and CMA3- stained metaphases, respectively. The third column shows chromosomes bearing AgNORs in the box. The arrows indicate the NOR-bearing chromosomes. Bar = 10 μm.
Metaphases of several cichlid species under different chromosome treatments. The species are indicated on the left. The first, second and third columns show C-banded, AgNOR- and CMA3- stained metaphases, respectively. The third column shows chromosomes bearing AgNORs in the box. The arrows indicate the NOR-bearing chromosomes. For some metaphases (without arrows) it was not possible to identify the NOR-carrying chromosomes. Bar = 10 µm.
The diploid number reported for the species in this study, in general are in agreement with the conserved 2n=48 chromosomes commonly found in South American cichlids and in contrast with the presence of 2n=44 chromosomes in African cichlids. All species, except
Chromosomal variability was observed in derived lineages, such as the
Chromosomal rearrangements such the ones reported here could lead to the karyotypic diversification of the species. In fact, chromosomal rearrangements have contributed to karyotypic evolution in a range of fishes, including the cichlids
Although the cichlid cytogenetics suggests that the ancestral karyotype (2n=48 st/a) could have undergone major changes (pericentric inversions, fusions, fissions and chromosomal translocations) in the macro-structure of the South American species (
C-banding analyses in this study revealed that the conserved pattern of heterochromatin distribution was mostly restricted to the pericentromeric regions of cichlid chromosomes, which has been commonly reported in American and African representatives but with variations in both groups (
Concerning the singular heterochromatic blocks reported here,
The fluorochrome CMA3 showed the presence of GC-rich blocks coinciding with AgNOR sites in all species, which is a common trait in cichlids. The variation in the extension of these blocks also matches the size variation in the AgNOR sites in some species. Additional CMA3+ blocks are uncommon patterns in cichlids species, but they have been reported here for some species. In addition, this trait has only been previously reported in the
With respect to AgNOR, length variation between homologous chromosomes could be explained by the duplication or deletion of 45S rDNA repeat units. All AgNOR sites in the species analyzed here are heterochromatic as aforementioned. The length variation detected and extensively observed in other organisms may be caused by the presence of repetitive sequences, errors during the replication process, unequal crossing-over (
The heterochromatin, CMA3+ blocks and AgNOR regions are classic cases of enriched repetitive elements regions, such as satellite DNA, transposable elements, and rDNA. Among cichlids, it has been reported that the pericentromeric regions, which are commonly evidenced by C-banding, are repositories for a great amount of repetitive elements, such as transposable elements (
The study was supported by Fundação de Amparo à Pesquisa do Estado de Mato Grosso (FAPEMAT), Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP), Coordenadoria de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).