[Show abstract][Hide abstract]ABSTRACT: Lutjanidae is a family of primarily marine and carnivorous fishes distributed in the Atlantic, Indian, and Pacific oceans,
with enormous economic and ecological importance. In order to better clarify the conservative chromosomal evolution of Lutjanidae,
we analyzed the evolutionary dynamics of 5 repetitive DNA classes in 5 Lutjanus and in 1 Ocyurus species from the Western Atlantic. The ribosomal 18S sites were generally located in a single chromosome pair, except for
L. jocu and L. alexandrei where they are found in 2 pairs. In turn, the 5S rDNA sites are unique, terminal and nonsyntenic with the 18S rDNA sites.
In 3 species analyzed, H3 hisDNA genes were found in 1 chromosomal pair. However, while L. jocu presented 2 H3 sites, O. chrysurus showed a noteworthy dispersion of this gene in almost all chromosomes of the karyotype. Retrotransposons Rex1 and Rex3 do
not exhibit any association with the explosive distribution of H3 sequences in O. chrysurus. The low compartmentalization of Rex elements, in addition to the general nondynamic distribution of ribosomal and H3 genes,
corroborate the karyotype conservatism in Lutjanidae species, also at the microstructural level. However, some “disturbing
evolutionary waves” can break down this conservative scenario, as evidenced by the massive random dispersion of H3 hisDNA
in the genome of O. chrysurus. The implication of the genomic expansion of H3 histone genes and their functionality remain unknown, although suggesting
that they have higher evolutionary dynamics than previously thought.
Full-text · Article · Jan 2016 · Journal of Heredity
[Show abstract][Hide abstract]ABSTRACT: Background:The genusClarias(Clariidae, Siluriformes) contains at least 61 species naturally spread over vast regions of Asia, India and Africa. However,Clariasspecies have also been introduced in many different countries and represent the most widespread catfishes in the world. These fishes are also known as“walking catfishes”due to their ability to move over land. A large degree of chromosomal variation has been previously found in this family, mainly using conventional cytogenetic investigations, with diploid chromosome numbers ranging between 48 and 100. In this
study, we analyzed the karyotype structure and distribution of four repetitive DNA sequences (5S and 18S rDNAs and (CA)15 and (GA)15microsatellites) in threeClariasspecies (C. batrachus, C. gariepinus, C. macrocephalus), as well as in a probable natural hybrid of the two latter species from different Thailand river basins.
Results:Clarias gariepinusandC. macrocephalushad 2n= 56 and 2n= 54, respectively, as well as karyotypes composed mainly by metacentric and submetacentric chromosomes. Their karyotypes differed in the number and location of 5S and 18S rDNA sites and in the degree of microsatelliteaccumulation. An intermediate chromosomal pattern incorporating those of the parental species was found in the probable hybrid, confirming its interspecific origin.
Clarias batrachushad 2n = 104 chromosomes and its karyotype was dominated by mainly acrocentric elements, indicating that unusual multiple centric fissions were involved in its karyotype differentiation. The karyotype of this species presented an unexpected dispersion of ribosomal DNAs, possessing 54 and 12 sites of 5S and 18S rDNAs, respectively, as well as a high accumulation and differential distribution of both microsatellite repeats, representing‘hot spots’ for chromosomal rearrangement.
Conclusion:Both conventional and molecular cytogenetic markers were useful tools for demonstrating remarkable evolutionary dynamism and highlighting multiple chromosomal rearrangements and hybridization events correlated with the notable karyotypic diversity of these walking catfishes.
Full-text · Article · Jan 2016 · Molecular Cytogenetics
[Show abstract][Hide abstract]ABSTRACT: Repetitive DNAs comprise the largest fraction of the eukaryotic genome. They include microsatellites or simple sequence repeats (SSRs), which play an important role in the chromosome differentiation among fishes. Rachycentron canadum is the only representative of the family Rachycentridae. This species has been focused on several multidisciplinary studies in view of its important potential for marine fish farming. In the present study, distinct classes of repetitive DNAs, with emphasis on SSRs, were mapped in the chromosomes of this species to improve the knowledge of its genome organization. Microsatellites exhibited a diversified distribution, both dispersed in euchromatin and clustered in the heterochromatin. The multilocus location of SSRs strengthened the heterochromatin heterogeneity in this species, as suggested by some previous studies. The colocalization of SSRs with retrotransposons and transposons pointed to a close evolutionary relationship between these repetitive sequences. A number of heterochromatic regions highlighted a greater complex organization than previously supposed, harboring a diversity of repetitive elements. In this sense, there was also evidence of colocalization of active genetic regions and different classes of repetitive DNAs in a common heterochromatic region, which offers a potential opportunity for further researches regarding the interaction of these distinct fractions in fish genomes.
[Show abstract][Hide abstract]ABSTRACT: With nearly 2,000 species, Gobiidae is the most specious family of the vertebrates. This high level of speciation is accompanied by conspicuous karyotypic modifications, where the role of repetitive sequences remains largely unknown. This study analyzed the karyotype of 2 species of the genus Gobionellus and mapped 18S and 5S ribosomal RNA genes and (CA) 15 microsatellite sequences onto their chromosomes. G. oceanicus (2n = 56; ♂ 12 metacentrics (m) + 4 submetacentrics (sm) + 1 subtelocentric (st) + 39 acrocentrics (a); ♀ 12m + 4sm + 2st + 38a) and G. stomatus (2n = 56; ♂ 20m + 14sm + 1st + 21a; ♀ 20m + 14sm + 2st + 20a) possess the highest diploid chromosome number among the Gobiidae and have different karyotypes. Both species share an XX/XY sex chromosome system with a large subtelocentric X and a small acrocentric Y chromosome which is rich in (CA) 15 sequences and bears 5S rRNA sites. Although coding and noncoding repetitive DNA sequences may be involved in the genesis or differentiation
Full-text · Article · Feb 2015 · Cytogenetic and Genome Research
[Show abstract][Hide abstract]ABSTRACT: tAcanthurus is a representative and widespread genus of marine fish that plays a key role in ecologicaldynamics of coral reefs. Three species are common along coastal reefs of Western Atlantic: A. coeruleus,A. bahianus, and A. chirurgus. The cytogenetic patterns of these species indicated sequential steps ofchromosomal rearrangements dating back 19–5 millions of years ago (M.a.) that accounted for their inter-specific differences. A. coeruleus (2n = 48; 2sm + 4st + 42a), A. bahianus (2n = 36; 12m + 2sm + 4st + 18a), andA. chirurgus (2n = 34; 12m + 2sm + 4st + 16a) share an older set of three chromosomal pairs that were orig-inated through pericentric inversions. A set of six large metacentric pairs formed by Robertsonian (Rb)translocations found in A. bahianus and A. chirurgus and a putative in tandem fusion found in A. chirurgusare more recent events. In the present study, new cytogenetic data are being reported for these threeAcanthurus species based on mapping of repetitive sequences such as ribosomal 18S and 5S rDNA andtelomeric repeats to improve their karyotype evolutionary analyses. The lack of interstitial telomericsequences (ITS) in spite of several centric fusions in A. bahianus and A. chirurgus might be related to thelong period of time after their occurrence (estimated in 5 M.a.). Furthermore, the homeologies amongthe chromosome pairs bearing ribosomal genes, in addition to other structural features, highlight largeconserved chromosomal regions in the three species. Our findings indicate that macrostructural changesoccurred during the cladogenesis of these species were not followed by conspicuous microstructuralrearrangements in the karyotypes.
Full-text · Article · Dec 2014 · Cytogenetic and Genome Research
[Show abstract][Hide abstract]ABSTRACT: Several chromosomal features of Gerreidae fish have been found to be conserved. In this group, it is unclear whether the high degree of chromosomal stasis is maintained when analyzing more dynamic regions of chromosomes, such as rDNA sites that generally show a higher level of variability. Thus, cytogenetic analyses were performed on 3 Atlantic species of the genus Eucinostomus using conventional banding (C-banding, Ag-NOR), AT- and GC-specific fluorochromes, and fluorescence in situ hybridization mapping of telomeric sequences and 5S and 18S rDNA sites. The results showed that although the karyotypical macrostructure of these species is similar (2n = 48 chromosomes, simple Ag-NORs seemingly located on homeologous chromosomes and centromeric heterochromatin pattern), there are differences in the positions of rDNA subunits 5S and 18S. Thus, the ribosomal sites have demonstrated to be effective cytotaxonomic markers in Eucinostomus, presenting a different evolutionary dynamics in relation to other chromosomal regions and allowing access to important evolutionary changes in this group.
Full-text · Article · Nov 2014 · Genetics and molecular research: GMR
[Show abstract][Hide abstract]ABSTRACT: n Carangidae, Caranx is taxonomically controversial because of slight morphological differences among species, as well as because of its relationship with the genus Carangoides. Cytogenetic data has contributed to taxonomic and phylogenetic classification for some groups of fish. In this study, we examined the chromosomes of Caranx latus, Caranx lugubris, and Carangoides bartholomaei using classical methods, including conventional staining, C-banding, silver staining for nuclear organizer regions, base-specific fluorochrome, and 18S and 5S ribosomal sequence mapping using in situ hybridization. These 3 species showed chromosome numbers of 2n = 48, simple nuclear organizer regions (pair 1), and mainly centromeric heterochomatin. However, C. latus (NF = 50) and C. bartholomaei (NF = 50) showed a structurally conserved karyotype compared with C. lugubris (NF = 54), with a larger number of 2-armed chromosomes. The richness of GC-positive heterochromatic segments and sites in 5S rDNA in specific locations compared to the other 2 species reinforce the higher evolutionary dynamism in C. lugubris. Cytogenetic aspects shared between C. latus and C. bartholomaei confirm the remarkable phylogenetic proximity between these genera.
Full-text · Article · Nov 2014 · Genetics and molecular research: GMR
[Show abstract][Hide abstract]ABSTRACT: Mechanisms of accumulation based on typical centromeric drive or of chromosomes carrying pericentric inversions are adjusted to the general karyotype differentiation in the principal Actinopterygii orders. Here, we show that meiotic drive in fish is also supported by preferential establishment of sex chromosome systems and B chromosomes in orders with predominantly bi-brachial chromosomes. The mosaic of trends acting at an infra-familiar level in fish could be explained as the interaction of the directional process of meiotic drive as background, modulated on a smaller scale by adaptive factors or specific karyotypic properties of each group, as proposed for the orthoselection model.
Full-text · Article · Nov 2014 · Anais da Academia Brasileira de Ciências
[Show abstract][Hide abstract]ABSTRACT: Rachycentron canadum , the only representative of the family Rachycentridae, has been the focus of biotechnological interest due to its significant potential in marine fish farming. The chromosome set of this species has been widely investigated with respect to the location of genes and multigene families. A FISH analysis was performed using 4 multigene families as probes, represented by 5S and 18S ribosomal genes and histones H2B-H2A and H3. Earlier data suggested that differential replication of heterochromatin could be partially associated with functional genes. Indeed, our results showed that the DNA contained in heterochromatic regions of R. canadum contains 5S and 18S ribosomal genes as well as the gene sequences of histones H2B-H2A and H3, which were colocalized. The distribution of H3 sequences in all heterochromatic regions, except in 13q, could indicate an important evolutionary role for this class of repetitive sequences. Besides, the presence of chromosome regions bearing multifunctional repetitive sequences formed by H2B-H2A/H3/18S rDNA and H2B-H2A/H3/5S rDNA clusterswas demonstrated for the first time in fishes. The implications of differential histone gene extension and its functionality in the karyotype of R. canadum remain unknown.
Full-text · Article · Oct 2014 · Cytogenetic and Genome Research
[Show abstract][Hide abstract]ABSTRACT: In this study, genetic differentiation between karyomorphs A (2n = 42) and D (2n = 39/40) of the wolf fish Hoplias malabaricus, which is comprised of several cryptic species that present a wide variety of diploid chromosome numbers and sex chromosome systems, resulting in the identification of seven distinct karyomorphs (A–G), was investigated using a combination of molecular and cytogenetic tools. Deep sequence divergences for both karyomorphs were observed and indicate a long period of reproductive isolation between karyomorphs A and D. Additionally, one individual with 61 chromosomes was identified, which, as far as is known, is the first case of natural triploidy resulting from the hybridization between these highly differentiated karyomorphs of H. malabaricus. Molecular and cytogenetic analyses revealed that this allotriploid specimen carries two sets of maternal chromosomes from karyomorph D (2n = 40) and one set of chromosomes from karyomorph A (n = 21). Moreover, ribosomal sites and active nucleolus organizer regions from both parental contributors were found in the triploid hybrid. Considering the significant genetic distances between karyomorphs A and D, one of the primary reasons for the lack of recurrent reports of hybridization in the H. malabaricus species complex may be due to post-zygotic barriers, such as hybrid sterility or unviability.
Full-text · Article · Sep 2014 · Journal of Fish Biology
[Show abstract][Hide abstract]ABSTRACT: The process of preferential chromosome segregation during meiosis has been suggested to be responsible for the predominance of certain chromosome types in the karyotypes of mammals, birds and insects. We developed an extensive analysis of the fixation of mono- or bibrachial chromosomes in the karyotypes of the large Actinopterygii fish group, a key link in the evolution of terrestrial vertebrates, in order to investigate the generality of meiotic drive in determining karyotypic macrotrends. Unlike mammals, fishes have markedly undergone several types of preferential chromosomal rearrangements throughout evolution. Data from the analyzed orders indicate a prevalence of karyotypes with few (<33%) or many (>66%) acrocentric chromosomes and a low number of karyotypes with balanced numbers of mono- and bi-brachial elements. Parallel trends towards a higher number of karyotypes with prevalence of monobrachial chromosomes occurred in phylogenetically close orders (e.g. Perciformes and Tetraodontiformes, and in the order Mugiliformes) and in clades with prevalence of bibrachial elements (e.g. Characiformes, Gymnotiformes, Siluriformes, and Cypriniformes). Some orders where fewer species were available for study, such as Atheriniformes and Anguilliformes, showed karyotype assemblages where both trends were present. Our results strongly suggest a primary role of meiotic drive in karyotypic evolution as indicated by the accumulation of monobrachial chromosomes in Perciformes and Cypriniformes, or bibrachial chromosomes in Siluriformes and Characiformes. Further examinations of the interaction between life history traits, environmental characteristics, and the fixation of chromosomal rearrangements would be exceedingly valuable.
[Show abstract][Hide abstract]ABSTRACT: Dolphinfishes (Coryphaenidae) are pelagic predators distributed throughout all tropical and subtropical oceans and are very important for commercial, traditional, and sport fishing. This small family contains the Coryphaena hippurus and Coryphaena equiselis species whose chromosomal aspects remain unknown, despite recent advances in cytogenetic data assimilation for Perciformes. In this study, both species were cytogenetically analyzed using different staining techniques (C-, Ag-, and CMA3 banding) and fluorescence in situ hybridization, to detect 18S rDNA and 5S rDNA. C. hippurus females exhibit 2n = 48 chromosomes, with 2m+4sm+42a (NF = 54). In C. equiselis, where both sexes could be analyzed, females displayed 2n = 48 chromosomes (2m+6sm+40a) and males exhibited 2n = 47 chromosomes (3m+6sm+38a) (NF = 56), indicating the presence of X1X1X2X2/X1X2Y multiple sex chromosomes. Sex-chromosome systems are rare in Perciformes, with this study demonstrating the first occurrence in a marine pelagic species. It remains unknown as to whether this system extends to other populations; however, these data are important with respect to evolutionary, phylogenetic, and speciation issues, as well as for elucidating the genesis of this unique sex system.
[Show abstract][Hide abstract]ABSTRACT: Repetitive DNA sequences play an important role in the structural and functional organization of chromosomes, especially in sex chromosome differentiation. The genus Triportheus represents an interesting model for such studies because all of its species analyzed so far contain a ZZ/ZW sex chromosome system. A close relationship has been found between the differentiation of the W chromosome and heterochromatinization, with the involvement of different types of repetitive DNA in this process. This study investigated several aspects of this association in the W chromosome of Triportheus trifurcatus (2n = 52 chromosomes), including the cytogenetic mapping of repetitive DNAs such as telomeric sequences (TTAGGG)n, microsatellites and retrotransposons. A remarkable heterochromatic segment on the W chromosome was observed with a preferential accumulation of (CAC)10, (CAG)10, (CGG)10, (GAA)10 and (TA)15. The retrotransposons Rex1 and Rex3 showed a general distribution pattern in the chromosomes, and Rex6 showed a different distribution on the W chromosome. The telomeric repeat (TTAGGG)n was highly evident in both telomeres of all chromosomes without the occurrence of ITS. Thus, the differentiation of the W chromosome of T. trifurcatus is clearly associated with the formation of heterochromatin and different types of repetitive DNA, suggesting that these elements had a prominent role in this evolutionary process.
[Show abstract][Hide abstract]ABSTRACT: Isolated oceanic islands constitute interesting model systems for the study of colonization processes, as several climatic and oceanographic phenomena have played an important role in the history of the marine ichthyofauna. The present study describes the presence of two morphotypes of Caranx lugubris, in the St. Peter and St. Paul Archipelago located in the mid-Atlantic. Morphotypes were compared in regard to their morphological and cytogenetic patterns, using C-banding, Ag-NORs, staining with CMA3/DAPI fluorochromes and chromosome mapping by dual-color FISH analysis with 5S rDNA and 18S rDNA probes. We found differences in chromosome patterns and marked divergence in body patterns which suggest that different populations of the Atlantic or other provinces can be found in the Archipelago of St. Peter and St. Paul.
Full-text · Article · Feb 2014 · Helgoland Marine Research
[Show abstract][Hide abstract]ABSTRACT: Erythrinus erythrinus, a Neotropical fish species of the Erythrinidae family, has a wide distribution in South America. Previous cytogenetic analysis showed that this species presents extensive karyotype diversity, with 4 karyomorphs (A-D) described herein. This study investigated the karyotypic structure of 2 new populations of E. erythrinus from the Brazilian Pantanal region, in order to improve the knowledge of the chromosomal diversity in this species. Both populations showed typical characteristics of karyomorph A, with 2n = 54 chromosomes (6 m + 2 st + 46 a), without differentiation between males and females. In addition, identical supernumerary B chromosomes, appearing as double minute ones, were also found in both the populations. These findings suggest the presence of mitotic instability in view of their high intra and inter-individual numerical variation. The presence of these chromosomes is likely a basal characteristic for this group, since the same kind of Bs also occurs in some other populations and karyomorphs of E. erythrinus. As such, they are important markers of biodiversity found in this nominal species, which probably corresponds to a species complex.
Full-text · Article · Feb 2014 · Genetics and molecular research: GMR
[Show abstract][Hide abstract]ABSTRACT: Chromosomal data for Myleus micans, a species of the subfamily Serrasalminae endemic to the São Francisco river basin, Brazil, are presented for the first time. The diploid number was found to be 2n=58, with 26M+18SM+8ST+6A chromosomes for both sexes. Heterochromatin was seen in the pericentromeric region in few chromosomes, and in the telomeric region only in the 27th pair. Multiple Ag-NORs were detected after silver nitrate staining, and located in four chromosomes. CMA3 staining also revealed four chromosomes sites, two of them not coincinding with those evidenced by silver nitrate. On the other hand, seven 18S rDNA sites were seen after fluorescent in situ hybridization (FISH), and only one chromosome pair bearing the 5S rDNA genes. The relationships between Myleus and the other Serrasalminae genera are discussed.
No preview · Article · Jan 2014 · Caryologia -Firenze-
[Show abstract][Hide abstract]ABSTRACT: Neotropical characiform fishes present two main trends of chromosomal evolution: some taxa show a heterogeneous pattern, with an extensive numerical and structural variation while others show a more homogeneous one, with a clear stability in their karyotype macrostructure. The implications of the populational features and some other conditions to these two general paths are discussed.
Full-text · Article · Jan 2014 · Caryologia -Firenze-