[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
Cytogenetic and Genome Research 02/2015; 144(4). DOI:10.1159/000373909 · 1.56 Impact Factor
[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.
Cytogenetic and Genome Research 12/2014; 254:62-66. DOI:10.1016/j.jcz.2014.11.003 · 1.56 Impact Factor
[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.
[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.
[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.
Anais da Academia Brasileira de Ciências 11/2014; DOI:10.1590/0001-3765201420130489 · 0.73 Impact Factor
[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.
Cytogenetic and Genome Research 10/2014; 2014(1):1-6. DOI:10.1159/000366301 · 1.56 Impact Factor
[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.
Journal of Fish Biology 09/2014; 85(5). DOI:10.1111/jfb.12526 · 1.66 Impact Factor
[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.
PLoS ONE 03/2014; 9(3):e90946. DOI:10.1371/journal.pone.0090946 · 3.23 Impact Factor
[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.
Helgoland Marine Research 02/2014; 68(1). DOI:10.1007/s10152-013-0365-0 · 1.36 Impact Factor
[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.
Genetics and molecular research: GMR 02/2014; · 0.78 Impact Factor
[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.
[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.
[Show abstract][Hide abstract] ABSTRACT: The family Characidae, one of the largest and more diversified fish families in the Neotropical region, is certainly not a monophyletic group, which is supported by the cytogenetic data showing its extensive chromosome variability. In this work, two species of the genus Serrapinnus, S. heterodon and S. piaba, from the São Francisco river basin were analyzed. Both species presented the same diploid number, 2n=52 chromosomes, and the same karyotypic formula, 16m+20sm+14st+2a. The heterochromatin distribution, evidenced by C-banding, was also similar between both species. On the other hand, two NORs were evidenced in S. heterodon, while a multiple NOR system was characterized in S. piaba, both confirmed by silver nitrate staining as well as by fluorescent in situ hybridization with 18S rDNA probe. Furthermore, two additional karyotypes (cytotypes) were observed in S. heterodon, with 15m+20sm+14st+3a and 17m+20sm+14st+la chromosomes, respectively, characterizing a structural chromosome polymorphism in the population. The differences between the three S. heterodon, karyotypic forms are probably due to pericentric inversions related to the 8th and 26th chromosome pairs.
[Show abstract][Hide abstract] ABSTRACT: Both males and females of the fish Prochilodus scrofa have a diploid number of 2n = 54. However, with the exception of a single female, all 59 specimens (25 ♀, 34 ♂) studied had 1–5 minutes accessory chromosomes. The unstable behavior of these chromosomes during mitosis and meiosis as well as their heterochromatic nature, as detected by C-banding, are characteristics that emphasize their supernumerary nature. This is the first report of chromosomes of this type in the Osteichthyes (Pisces).
[Show abstract][Hide abstract] ABSTRACT: In the present study, 10 neotropical species of family Cichlidae (Pisces, Perciformes) were submitted to analysis of the nucleolar organizing regions (NORs). In 8 of these species, the NORs were located in the first pair in the complement and coincided with the secondary constrictions observed there, whereas in Cichlasoma facetum and Geophagus brasiliensis the NORs were located in another chromosome pair. The possibility that the predominant location of NORs in the 1st pair in the karyotype indicates a more primitive condition of this group of fish is discussed. Variations in NOR size between homologous chromosomes of some species were also observed.