Short Communication |
Corresponding author: Fabilene Gomes Paim ( fabillene@yahoo.com.br ) Academic editor: Eugene Krysanov
© 2017 Fabilene Gomes Paim, Leandro Aragão da Hora Almeida, Paulo Roberto Antunes de Mello Affonso, Patrícia Elda Sobrinho-Scudeler, Claudio Oliveira, Débora Diniz.
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:
Paim FG, Almeida LAH, Affonso PRAM, Sobrinho-Scudeler PE, Oliveira C, Diniz D (2017) Chromosomal stasis in distinct families of marine Percomorpharia from South Atlantic. Comparative Cytogenetics 11(2): 299-307. https://doi.org/10.3897/CompCytogen.v11i2.11942
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The weakness of physical barriers in the marine environment and the dispersal potential of fish populations have been invoked as explanations of the apparent karyotype stasis of marine Percomorpha, but several taxa remain poorly studied cytogenetically. To increase the chromosomal data in this fish group, we analyzed cytogenetically three widespread Atlantic species from distinct families: Chaetodipterus faber Broussonet, 1782 (Ephippidae), Lutjanus synagris Linnaeus, 1758 (Lutjanidae) and Rypticus randalli Courtenay, 1967 (Serranidae). The three species shared a karyotype composed of 2n=48 acrocentric chromosomes, single nucleolus organizer regions (NORs) and reduced amounts of centromeric heterochromatin. A single NOR-bearing pair was identified in all species by physical mapping of 18S rDNA while non-syntenic 5S rRNA genes were located at centromeric region of a single pair. The similar karyotypic macrostructure observed in unrelated groups of Percomorpharia reinforces the conservative karyoevolution of marine teleosteans. Nonetheless, the species could be differentiated based on the pair bearing ribosomal cistrons, revealing the importance of microstructural analyses in species with symmetric and stable karyotypes.
Cytotaxonomy, Ephippiformes , ribosomal genes, South Atlantic
Perciformes have long been regarded as the largest order of vertebrates with nearly 10.000 species, 1540 genera, and 160 families, most of them inhabiting the marine environment (
In general, chromosomal studies in marine Percomorpharia reveal stable karyotypes composed of 2n=48 and a predominance of acrocentric pairs. Indeed, the presence of 24 acrocentric pairs is shared by several species from distinct families of Perciformes (
One of the hypotheses invoked to explain the conserved karyoevolution of this fish group refers to their biological traits, such as the absence or fragility of physical barriers in oceans that favor the connectivity among populations, wide range of most species and chromosomal or genomic peculiarities (
On the other hand, most families of marine Percomorpharia have been divided into two groups based on the rate of karyotype changes, comprising families of high karyotype stability or with moderate rates of karyoevolution (
To test the corollary that the high dispersal and gene flow associated with the weakness of geographic barriers accounts for the chromosomal stasis in marine Percomorpharia groups, we analyzed cytogenetically three widespread Atlantic species from distinct families: Chaetodipterus faber (Ephippidae), Lutjanus synagris (Lutjanidae) and Rypticus randalli (Serranidae). Besides inferring their karyoevolutionary pathways, we provided the first cytogenetic report in C. faber and R. randalli.
The specimens of Chaetodipterus faber (N=7, 1♀, 6 unidentified sex), Lutjanus synagris (N=8, 4♀, 4 unidentified sex), and Rypticus randalli (N=10, 3♂, 2♀, 5 unidentified sex) were collected by gillnets and snorkeling in Camamu Bay and Boipeba Island, located on the coast of Bahia, northeastern Brazil, South Atlantic. The vouchers were deposited in the Laboratory of Genetics of Aquatic Organisms (LAGOA) from Universidade Estadual do Sudoeste da Bahia, in Jequié, Bahia.
After collection, the specimens were mitotically stimulated by inoculation of fungal antigens and kept in fish tanks for 24 to 72 h (
The heterochromatin regions were visualized by C-banding (
The metaphase spreads were photographed using an epifluorescence microscope Olympus BX-51 equipped with the software ImagePro-Plus v. 6.2. (Media Cybernetics).The chromosomes were classified according to their arm ratio (
The species C. faber, L. synagris, and R. randalli share a modal diploid number of 2n = 48, composed exclusively of acrocentric chromosomes (Figure
Single NORs were invariably detected, but located at distinct pairs according to each species (Figure
The 18S rDNA sites were located at interstitial positions on the long arms of pairs 3, 20, and 23 in C. faber, R. randalli, and L. synagris, respectively. Size differences in the 18S rDNA clusters between homologs were observed in C. faber and R. randalli, as also revealed by silver nitrate staining (Figure
Karyotypes of Chaetodipterus faber (A), Lutjanus synagris (B), and Rypticus randalli (C) with 2n=48 acrocentric chromosomes after conventional Giemsa-staining (top), C-banding (center) and double FISH with 18S (green signals) and 5S (magenta signals) rDNA probes (bottom). In boxes, the pairs bearing nucleolus organizer regions after silver nitrate staining (Ag-NORs).
The three species studied in the present work shared a karyotype composed of 24 pairs of acrocentric chromosomes, regarded as a plesiomorphic feature for Perciformes sensu
Likewise, lutjanids (snappers) from the Brazilian coast invariably present 2n=48 acrocentric chromosomes (
The karyotypic results in C. faber represent the first cytogenetic data in the order Ephippiformes (
Besides the role of dispersal and formation of large populations (
The nucleolus organizer regions (NORs) are considered a highly informative cytogenetic marker in teleosteans (Gornung 2008). The presence of single NORs at pericentromeric region is considered the plesiomorphic condition for several families in Percomorpharia, particularly those characterized by species with 2n=48a (
On the other hand, the NOR-bearing pair seems to differ according to each species in some families, like Lutjanidae (
The identification of 5S rRNA genes was also informative to the karyotypic analyses of studied species. As commonly reported in marine fish, particularly Perciformes (Motta Neto et al. 2011a,
In conclusion, the present results highlight the extensive karyotype macrostructure stasis in marine Percomorpha, since several cytogenetic features were shared by three species from distinct families and groups within Percomorpharia, corroborating the hypothesis of conserved karyotype macrostructure in widespread marine species. However, the evolutionary dynamics of ribosomal genes seem to play a major role in the cytotaxonomy of marine fish, as pointed out in typical marine families with basal karyotypes like Lutjanidae (
The authors are grateful to FAPESB (PNE0019/2011, APP0064/2011) and “INCT de Ambientes Marinhos Tropicais” (SICONV 762228/2011) for the financial support, and ICMBIO/SISBIO for authorizing the collection of studied species (licenses 31360-1 and 27027-2).