Chromosomal mapping of repetitive DNA in Melipona seminigra merrillae Cockerell, 1919 (Hymenoptera, Apidae, Meliponini).

Melipona Illiger, 1806 is represented by 74 known species of stingless bees, distributed throughout the Neotropical region. Cytogenetically it is the most studied stingless bee genus of the tribe Meliponini. Member species are divided in two groups based on the volume of heterochromatin. This study aim was to analyze the composition and organization of chromatin of the stingless bee subspecies Melipona seminigra merrillae Cockerell, 1919 using classical and molecular cytogenetic techniques, so contributing to a better understanding of the processes of chromosomal changes within the genus. We confirm that M. seminigra merrillae has a chromosome number of 2n = 22 and n = 11, results that differ from those reported for the genus in the absence of B chromosomes. The heterochromatic pattern revealed a karyotype composed of chromosomes with a high heterochromatin content, which makes it difficult to visualize the centromere. Silver nitrate impregnation (Ag-NOR) showed transcriptionally active sites on the second chromosomal pair. Staining of base-specific fluorophores DAPI-CMA3 indicated a homogeneous distribution of intensely DAPI-stained heterochromatin, while CMA3 markings appeared on those terminal portions of the chromosomes corresponding to euchromatin. Similar to Ag-NOR, fluorescence in situ hybridization (FISH) with 18S ribosomal DNA probe revealed distinct signals on the second pair of chromosomes. Microsatellite mapping (GA)15 showed markings distributed in euchromatic regions, while mapping with (CA)15 showed marking patterns in heterochromatic regions, together with a fully marked chromosome pair. Microsatellite hybridization, both in heterochromatic and euchromatic regions, may be related to the activity of transposable elements. These are capable of forming new microsatellites that can be dispersed and amplified in different regions of the genome, demonstrating that repetitive sequences can evolve rapidly, thus resulting in within-genus diversification.

Looking for genetic effects of polluted anthropized environments on Caiman crocodilus crocodilus (Reptilia, Crocodylia): A comparative genotoxic and chromosomal analysis.

The Amazon aquatic ecosystems have been modified by the human population growth, going through changes in their water bodies and aquatic biota. The spectacled alligator (Caiman crocodilus crocodilus) has a wide distribution and adaptability to several environments, even those polluted ones. This study aimed to investigate if a Caiman species living in urban streams of Manaus city (Amazonas State, Brazil) is affected by environmental pollution. For that, it was used classical and molecular cytogenetic procedures, in addition to micronucleus and comet assays. Although the karyotype macrostructure remains unaltered (2 n = 42 chromosomes; 24 t + 18 m/sm; NF = 60), the genotoxic analysis and the cytogenetic mapping of repetitive DNA sequences demonstrated that polluted environments alter the genome of the specimens, affecting both the chromosomal organization and the genetic material.

Cytogenetic analysis of three Ctenidae species (Araneae) from the Amazon.

Cytogenetic characterization was performed on three wandering spiders: Ctenus amphora Mello-Leitão, 1930, C. crulsi Mello-Leitão, 1930 and C. villasboasi Mello-Leitão, 1949. The three species had similar karyotypes, with 2n = 28 (26 + X1X20) in males, with sex chromosomes exhibiting positive heteropicnosis in meiotic cells. 18S rDNA mapping revealed gene sites at the terminal region of one chromosomal pair for all species, with one C. crulsi individual, showing markings in two pairs. C. villasboasi showed markers only in the pachytene phase. The distribution pattern of constitutive heterochromatin was found to be characteristic for the genus, with markings in the centromeric region of all chromosomes, suggesting an acrocentric morphology for all chromosomes of the three analysed species. The results support the fusion of sex chromosomes as an evolutionary tendency for this spider group.

Effects of environmental pollution on the rDNAomics of Amazonian fish.

Pollution is a growing environmental problem throughout the world, and the impact of human activities on biodiversity and the genetic variability of natural populations is increasingly preoccupying, given that adaptive processes depend on this variability, in particular that found in the repetitive DNA. In the present study, the mitochondrial DNA (COI) and the distribution of repetitive DNA sequences (18S and 5S rDNA) in the fish genome were analysed in fish populations inhabiting both polluted and unpolluted waters in the northern Amazon basin. The results indicate highly complex ribosomal sequences in the fish genome from the polluted environment because these sequences are involved primarily in the maintenance of genome integrity, mediated by a systematic increase in the number of copies of the ribosomal DNA in response to changes in environmental conditions.

Differential chromosomal organization between Saguinus midas and Saguinus bicolor with accumulation of differences the repetitive sequence DNA.

Saguinus is the largest and most complex genus of the subfamily Callitrichinae, with 23 species distributed from the south of Central America to the north of South America with Saguinus midas having the largest geographical distribution while Saguinus bicolor has a very restricted one, affected by the population expansion in the state of Amazonas. Considering the phylogenetic proximity of the two species along with evidence on the existence of hybrids between them, as well as cytogenetic studies on Saguinus describing a conserved karyotypic macrostructure, we carried out a physical mapping of DNA repeated sequences in the mitotic chromosome of both species, since these sequences are less susceptible to evolutionary pressure and possibly perform an important function in speciation. Both species presented 2n = 46 chromosomes; in S. midas, chromosome Y is the smallest. Multiple ribosomal sites occur in both species, but chromosome pairs three and four may be regarded as markers that differ the species when subjected to G banding and distribution of retroelement LINE 1, suggesting that it may be cytogenetic marker in which it can contribute to identification of first generation hybrids in contact zone. Saguinus bicolor also presented differences in the LINE 1 distribution pattern for sexual chromosome X in individuals from different urban fragments, probably due to geographical isolation. In this context, cytogenetic analyses reveal a differential genomic organization pattern between species S. midas and S. bicolor, in addition to indicating that individuals from different urban fragments have been accumulating differences because of the isolation between them.

Karyotypic Comparison of Hoplias malabaricus (Bloch, 1794) (Characiformes, Erythrinidae) in Central Amazon.

Hoplias malabaricus comprises seven karyomorphs (A-G) and evolutionary units have been described in some of them. In this study, the karyotypic composition and genomic organization of individual H. malabaricus from Central Amazon are described and to verify whether they can be classified according to known karyomorphs. Individuals from the Ducke Reserve have 2n = 42 chromosomes, similar to karyomorph A. Individuals from Catalão Lake and Marchantaria Island exhibit 2n = 40 chromosomes, similar to karyomorph C. Regarding the constitutive heterochromatin, individuals from all locations present centromeric/pericentromeric blocks, in addition to some bitelomeric and interstitial markings. The number of chromosomes with nucleolar organizer region, 5S rDNA and 18S rDNA sites varied among the different locations. The Rex 3 element has a compartmentalized distribution at the terminal and centromeric regions of most chromosomes, with subtle differences among populations. Fluorescence in situ hybridization performed with a telomeric probe allowed the detection of these regions only at the terminal ends of the chromosomes. Thus, only the chromosomal macrostructure (karyomorphs A-G) is not sufficient to establish evolutionary units within the H. malabaricus group, considering differences in the genome organization that are found among their populations. Such differences in the genomic organization could be mainly caused by the sedentary habits of this species.

Intense genomic reorganization in the genus Oecomys (Rodentia, Sigmodontinae): comparison between DNA barcoding and mapping of repetitive elements in three species of the Brazilian Amazon.

Oecomys Thomas, 1906 is one of the most diverse and widely distributed genera within the tribe Oryzomyini. At least sixteen species in this genus have been described to date, but it is believed this genus contains undescribed species. Morphological, molecular and cytogenetic study has revealed an uncertain taxonomic status for several Oecomys species, suggesting the presence of a complex of species. The present work had the goal of contributing to the genetic characterization of the genus Oecomys in the Brazilian Amazon. Thirty specimens were collected from four locations in the Brazilian Amazon and three nominal species recognized: Oecomys auyantepui (Tate, 1939), Oecomys bicolor (Tomes, 1860) and Oecomys rutilus (Anthony, 1921). COI sequence analysis grouped Oecomys auyantepui, Oecomys bicolor and Oecomys rutilus specimens into one, three and two clades, respectively, which is consistent with their geographic distribution. Cytogenetic data for Oecomys auyantepui revealed the sympatric occurrence of two different diploid numbers, 2n=64/NFa=110 and 2n=66/NFa=114, suggesting polymorphism while Oecomys bicolor exhibited 2n=80/NFa=142 and Oecomys rutilus 2n=54/NFa=90. The distribution of constitutive heterochromatin followed a species-specific pattern. Interspecific variation was evident in the chromosomal location and number of 18S rDNA loci. However, not all loci showed signs of activity. All three species displayed a similar pattern for 5S rDNA, with only one pair carrying this locus. Interstitial telomeric sites were found only in Oecomys auyantepui. The data presented in this work reinforce intra- and interspecific variations observed in the diploid number of Oecomys species and indicate that chromosomal rearrangements have led to the appearance of different diploid numbers and karyotypic formulas.

Differential repetitive DNA composition in the centromeric region of chromosomes of Amazonian lizard species in the family Teiidae.

Differences in heterochromatin distribution patterns and its composition were observed in Amazonian teiid species. Studies have shown repetitive DNA harbors heterochromatic blocks which are located in centromeric and telomeric regions in Ameiva ameiva (Linnaeus, 1758), Kentropyx calcarata (Spix, 1825), Kentropyx pelviceps (Cope, 1868), and Tupinambis teguixin (Linnaeus, 1758). In Cnemidophorus sp.1, repetitive DNA has multiple signals along all chromosomes. The aim of this study was to characterize moderately and highly repetitive DNA sequences by C ot1-DNA from Ameiva ameiva and Cnemidophorus sp.1 genomes through cloning and DNA sequencing, as well as mapping them chromosomally to better understand its organization and genome dynamics. The results of sequencing of DNA libraries obtained by C ot1-DNA showed that different microsatellites, transposons, retrotransposons, and some gene families also comprise the fraction of repetitive DNA in the teiid species. FISH using C ot1-DNA probes isolated from both Ameiva ameiva and Cnemidophorus sp.1 showed these sequences mainly located in heterochromatic centromeric, and telomeric regions in Ameiva ameiva, Kentropyx calcarata, Kentropyx pelviceps, and Tupinambis teguixin chromosomes, indicating they play structural and functional roles in the genome of these species. In Cnemidophorus sp.1, C ot1-DNA probe isolated from Ameiva ameiva had multiple interstitial signals on chromosomes, whereas mapping of C ot1-DNA isolated from the Ameiva ameiva and Cnemidophorus sp.1 highlighted centromeric regions of some chromosomes. Thus, the data obtained showed that many repetitive DNA classes are part of the genome of Ameiva ameiva, Cnemidophorus sp.1, Kentroyx calcarata, Kentropyx pelviceps, and Tupinambis teguixin, and these sequences are shared among the analyzed teiid species, but they were not always allocated at the same chromosome position.

Comparative Cytotaxonomy of Two Species of Fish from the Genus Satanoperca Reveals the Presence of a B Chromosome.

The taxonomy of Satanoperca spp. is still unresolved, especially because coloring, one of the main diagnostic characters, is variable among species of this genus. Thus, the aim of this study was to elucidate the relationship between the genome and the organization of the chromosome in two Satanoperca species. Our main goal was to develop a method to better differentiate taxa and understand the evolution of Satanoperca jurupari and Satanoperca lilith karyotypes, which we analyzed with classical and molecular cytogenetics. Both species have the same diploid number (2n) of 48 and location of 5S rDNA sites on pair 5. Nonetheless, the distribution of heterochromatin and 18S rDNA sites followed a species-specific pattern. The interstitial telomeric sites were not highlighted in either species. Regardless, a single B chromosome was identified in some metaphases of S. lilith. These data show that Satanoperca species harbor chromosomal features that can be used to identify the two species of Satanoperca studied here, allowing for the use of cytogenetic markers to make taxonomic inferences within the genus.

Genomic Organization Under Different Environmental Conditions: Hoplosternum Littorale as a Model.

The Amazon has abundant rivers, streams, and floodplains in both polluted and nonpolluted environments, which show great adaptability. Thus, the goal of this study was to map repetitive DNA sequences in both mitotic chromosomes and erythrocyte micronuclei of tamoatás from polluted and nonpolluted environments and to assess the possible genotoxic effects of these environments. Individuals were collected in Manaus, Amazonas (AM), and submitted to classical and molecular cytogenetic techniques, as well as to a blood micronucleus test. Diploid number equal to 60 chromosomes are present in all individuals, with 18S ribosomal DNA sites present in one chromosome pair and no interstitial telomeric sites on chromosomes. The micronucleus test showed no significant differences in pairwise comparisons between environments or collection sites, but the Rex3 retroelement was dispersed on the chromosomes of individuals from unpolluted environments and compartmentalized in individuals from polluted environments. Divergent numbers of 5S rDNA sites are present in individuals from unpolluted and polluted environments. The mapping of repetitive sequences revealed that micronuclei have different compositions both intra- and interindividually that suggests different regions are lost in the formation of micronuclei, and no single fragile region undergoes breaks, although repetitive DNA elements are involved in this process.

Karyoevolution in Potamorhina (Cope, 1878) (Ostariophysi, Curimatidae): Using Repetitive DNA for the Elucidation of Genome Organization.

Some families of Characiformes present the tendency toward stability of the karyotypic macrostructure as Curimatidae, which contains species with a 2n = 54 karyotype and metacentric and submetacentric chromosomes, however, some Potamorhina species contradict to this tendency. Some species of the central Amazon exhibit different diploid number and show intraspecific variation in the location of heterochromatin. By performing cytogenetic characterization by localization of heterochromatin and the nucleolus organizer region, as well as physical chromosome mapping using probes targeting 5S and 18S ribosomal DNA (rDNA), retroelement of Xiphophorus 1 (Rex1), Rex3, telomeres, and tropomyosin 1 (TPM1), we attempted to understand the evolutionary mechanisms involved in the differentiation of the Potamorhina species. The analyses showed that the heterochromatic regions of the examined species are distinct and transposable elements are involved in this evolutionary process, considering that the dynamic regions of the genome appear to include the terminal regions and particularly the heterochromatin-rich centromeric regions, which are involved in fission and fusion processes and promote the differentiation of chromosome pairs that bear ribosomal sites; these pairs were similar in the central Amazon species. Thus, we propose a phylogeny for this genus.

Intra-generic and interspecific karyotype patterns of Leptodactylus and Adenomera (Anura, Leptodactylidae) with inclusion of five species from Central Amazonia.

The genera Leptodactylus and Adenomera comprise 92 species distributed throughout the Neotropical region. These species have a modal diploid chromosome number 2n = 22. However, chromosome rearrangements are evident in the differentiation of five intra-generic groups in the genus Leptodactylus (L. fuscus, L. latrans, L. marmoratus (formally composed by the species of the genus Adenomera), L. melanonotus, L. pentadactylus), yet it is not clear if there is a karyotype pattern for each group. Aiming to understand the intra-generic and interspecific karyotype patterns of Leptodactylus and Adenomera, cytogenetic analyses were performed in A. andreae, L. macrosternum, L. pentadactylus, L. petersii, and L. riveroi using conventional staining, C-banding, nucleolus organizer region (NOR) and hybridization in situ fluorescent (FISH). The karyotype of Leptodactylus riveroi was described for the first time. Adenomera andreae had 2n = 26, while the remaining species 2n = 22. The NOR was found on pair No. 8 of A. andreae, L. macrosternum, L. pentadactylus, and L. riveroi, whereas L. petersii had it on pairs Nos. 6 and 10. These locations were confirmed by the FISH with 18S rDNA probe, except for pair No. 10 of L. petersii. The C-banding pattern was evident at the centromeres of chromosomes of all species and some interspecific variations were also observed. 2n = 22 was observed in the species of the L. latrans group, as well as in the intra-generic groups L. fuscus and L. pentadactylus; in the L. melanonotus group there were three diploid chromosome numbers 2n = 20, 22 and 24; and a larger variation in 2n was also evident in the L. marmoratus group.

Chromosomal distribution of microsatellite repeats in Amazon cichlids genome (Pisces, Cichlidae).

Fish of the family Cichlidae are recognized as an excellent model for evolutionary studies because of their morphological and behavioral adaptations to a wide diversity of explored ecological niches. In addition, the family has a dynamic genome with variable structure, composition and karyotype organization. Microsatellites represent the most dynamic genomic component and a better understanding of their organization may help clarify the role of repetitive DNA elements in the mechanisms of chromosomal evolution. Thus, in this study, microsatellite sequences were mapped in the chromosomes of Cichla monoculus Agassiz, 1831, Pterophyllum scalare Schultze, 1823, and Symphysodon discus Heckel, 1840. Four microsatellites demonstrated positive results in the genome of Cichla monoculus and Symphysodon discus, and five demonstrated positive results in the genome of Pterophyllum scalare. In most cases, the microsatellite was dispersed in the chromosome with conspicuous markings in the centromeric or telomeric regions, which suggests that sequences contribute to chromosome structure and may have played a role in the evolution of this fish family. The comparative genome mapping data presented here provide novel information on the structure and organization of the repetitive DNA region of the cichlid genome and contribute to a better understanding of this fish family's genome.

Cytogenetic analyses of five amazon lizard species of the subfamilies Teiinae and Tupinambinae and review of karyotyped diversity the family Teiidae.

Lizards of the family Teiidae (infraorder Scincomorpha) were formerly known as Macroteiidae. There are 13 species of such lizards in the Amazon, in the genera Ameiva (Meyer, 1795), Cnemidophorus (Wagler, 1830), Crocodilurus (Spix, 1825), Dracaena (Daudin, 1801), Kentropyx (Spix, 1825) and Tupinambis (Daudin, 1802). Cytogenetic studies of this group are restricted to karyotype macrostructure. Here we give a compilation of cytogenetic data of the family Teiidae, including classic and molecular cytogenetic analysis of Ameiva ameiva (Linnaeus, 1758), Cnemidophorus sp.1, Kentropyx calcarata (Spix, 1825), Kentropyx pelviceps (Cope, 1868) and Tupinambis teguixin (Linnaeus, 1758) collected in the state of Amazonas, Brazil. Ameiva ameiva, Kentropyx calcarata and Kentropyx pelviceps have 2n=50 chromosomes classified by a gradual series of acrocentric chromosomes. Cnemidophorus sp.1 has 2n=48 chromosomes with 2 biarmed chromosomes, 24 uniarmed chromosomes and 22 microchromosomes. Tupinambis teguixin has 2n=36 chromosomes, including 12 macrochromosomes and 24 microchromosomes. Constitutive heterochromatin was distributed in the centromeric and terminal regions in most chromosomes. The nucleolus organizer region was simple, varying in its position among the species, as evidenced both by AgNO3 impregnation and by hybridization with 18S rDNA probes. The data reveal a karyotype variation with respect to the diploid number, fundamental number and karyotype formula, which reinforces the importance of increasing chromosomal analyses in the Teiidae.

Karyotypic diversity in seven Amazonian anurans in the genus Hypsiboas (family Hylidae).

BACKGROUND: Hypsiboas species have been divided into seven groups using morphological and genetic characters, but for most of the species, there is no cytogenetic information available. A cytogenetic analysis using conventional staining, C-banding, silver staining, and fluorescence in situ hybridization (FISH) with telomeric sequence probes were used to investigate the karyotype of seven Amazon species of the genus Hypsiboas belonging to the following intrageneric groups: H. punctatus (H. cinerascens), H. semilineatus (H. boans, H. geographicus, and H. wavrini), and H. albopunctatus (H. lanciformis, H. multifasciatus, and H. raniceps). The aim was to differentiate between the karyotypes and use the chromosomal markers to distinguish between the Hypsiboas groups. The data were compared with a previous phylogenetic proposal for these anurans. In addition, H. lanciformis, H. boans, and H. wavrini are described here for the first time, and we characterize the diploid numbers for H. cinerascens, H. geographicus, H. multifasciatus, and H. raniceps. RESULTS: The diploid number for all of the species analyzed was 24, with the exception of Hypsiboas lanciformis, which had 2n = 22 chromosomes. The constitutive heterochromatin distribution, nucleolar organizer region locations, and interstitial telomeric sites differed between the species. A hypothesis that the heterochromatic patterns are evolving is proposed, with the divergence of the groups probably involving events such as an increase in the heterochromatin in the species of the H. semilineatus group. The FISH conducted with the telomeric probes detected sites in the terminal regions of all of the chromosomes of all species. Interstitial telomeric sites were detected in three species belonging to the H. semilineatus group: H. boans, H. geographicus, and H. wavrini. CONCLUSION: The results of this study reinforce the complexity previously observed within the genus Hypsiboas and in the different groups that compose this taxon. More studies are needed focusing on this group and covering larger sampling areas, especially in the Brazilian Amazon, to improve our understanding of this fascinating and complex group.

Evolutionary dynamics of retrotransposable elements Rex1, Rex3 and Rex6 in neotropical cichlid genomes.

BACKGROUND: Transposable elements (TEs) have the potential to produce broad changes in the genomes of their hosts, acting as a type of evolutionary toolbox and generating a collection of new regulatory and coding sequences. Several TE classes have been studied in Neotropical cichlids; however, the information gained from these studies is restricted to the physical chromosome mapping, whereas the genetic diversity of the TEs remains unknown. Therefore, the genomic organization of the non-LTR retrotransposons Rex1, Rex3, and Rex6 in five Amazonian cichlid species was evaluated using physical chromosome mapping and DNA sequencing to provide information about the role of TEs in the evolution of cichlid genomes. RESULTS: Physical mapping revealed abundant TE clusters dispersed throughout the chromosomes. Furthermore, several species showed conspicuous clusters accumulation in the centromeric and terminal portions of the chromosomes. These TE chromosomal sites are associated with both heterochromatic and euchromatic regions. A higher number of Rex1 clusters were observed among the derived species. The Rex1 and Rex3 nucleotide sequences were more conserved in the basal species than in the derived species; however, this pattern was not observed in Rex6. In addition, it was possible to observe conserved blocks corresponding to the reverse transcriptase fragment of the Rex1 and Rex3 clones and to the endonuclease of Rex6. CONCLUSION: Our data showed no congruence between the Bayesian trees generated for Rex1, Rex3 and Rex6 of cichlid species and phylogenetic hypothesis described for the group. Rex1 and Rex3 nucleotide sequences were more conserved in the basal species whereas Rex6 exhibited high substitution rates in both basal and derived species. The distribution of Rex elements in cichlid genomes suggests that such elements are under the action of evolutionary mechanisms that lead to their accumulation in particular chromosome regions, mostly in heterochromatins.

Structure and organization of the mitochondrial DNA control region with tandemly repeated sequence in the Amazon ornamental fish.

Tandemly repeated sequences are a common feature of vertebrate mitochondrial DNA control regions. However, questions still remain about their mode of evolution and function. To better understand patterns of variation in length and to explore the existence of previously described domain, we have characterized the control region structure of the Amazonian ornamental fish Nannostomus eques and Nannostomus unifasciatus. The control region ranged from 1121 to 1142 bp in length and could be separated into three domains: the domain associated with the extended terminal associated sequences, the central conserved domain, and the conserved sequence blocks domain. In the first domain, we encountered a sequence repeated 10 times in tandem (variable number tandem repeat (VNTR)) that could adopt an "inverted repetitions" type structural conformation. The results suggest that the VNTR pattern encountered in both N. eques and N. unifasciatus is consistent with the prerequisites of the illegitimate elongation model in which the unequal pairing of the chains near the 5'-end of the control region favors the formation of repetitions.

Repetitive sequences associated with differentiation of W chromosome in Semaprochilodus taeniurus.

The possible origins and differentiation of a ZZ/ZW sex chromosome system in Semaprochilodus taeniurus, the only species of the family Prochilodontidae known to possess heteromorphic sex chromosomes, were examined by conventional (C-banding) and molecular (cross-species hybridization of W-specific WCP, Fluorescence in situ hybridization (FISH) with telomere (TTAGGG)n, and Rex1 probes) cytogenetic protocols. Several segments obtained by W-specific probe were cloned, and the sequences localized on the W chromosome were identified by DNA sequencing and search of nucleotide collections of the NCBI and GIRI using BLAST and CENSOR, respectively. Blocks of constitutive heterochromatin in chromosomes of S. taeniurus were observed in the centromere of all autosomal chromosomes and in the terminal, interstitial, and pericentromeric regions of the W chromosome, which did not demonstrate interstitial telomeric sites with FISH of the telomere probe. The Rex1 probe displayed a compartmentalized distribution pattern in some chromosomes and showed signs of invasion of the pericentromeric region in the W chromosome. Chromosomal painting with the W-specific WCP of S. taeniurus onto its own chromosomes showed complete staining of the W chromosome, centromeric sites, and the ends of the Z chromosome, as well as other autosomes. However, cross-species painting using this WCP on chromosomes of S. insignis, Prochilodus lineatus, and P. nigricans did not reveal a proto-W element, but instead demonstrated scattered positive signals of repetitive DNAs. Identification of the W-specific repetitive sequences showed high similarity to microsatellites and transposable elements. Classes of repetitive DNA identified in the W chromosome suggested that the genetic degeneration of this chromosome in S. taeniurus occurred through accumulation of these repetitive DNAs.

Epifluorescence and light microscopy evidencing structural and functional polymorphism of ribosomal DNA in fish (Teleostei: Astyanax fasciatus).

New karyotypic data are presented for the Astyanax fasciatus species complex from four different locations on the Upper Tibagi River in the state of Paraná, Brazil. Chromosome markers were analyzed using conventional (Ag-NOR) and molecular (FISH with 18S biotinylated probes) methods. Two cytotypes were found in cell counts with diploid number 2n=48 chromosomes and 2n=50 chromosomes, previously denominated Cytotype A and B, respectively. Two specific patterns of Ag-NORs markers (ribosomal gene activity) were found, with intra-population and inter-population variations. Cytotype A exhibited two to three chromosomes with NOR sites in the metaphases analyzed. In Cytotype B specimens, up to three markers were found, demonstrating greater intra-population and inter-population variation. All individuals with only one chromosome pair with NORs were located in the telomeric region of the short arm of Chromosome 5. This characteristic was interpreted as ancestral for the species. Another identified pattern revealed a site in the telomeric region probably in the long arm of Chromosome 4 and another submetacentric chromosome with bitelomeric marks exclusively in specimens with 2n=50 chromosomes. In the FISH analysis (ribosomal gene structure), five to seven markers were identified in Cytotype A and three to seven markers were identified in Cytotype B. Structural chromosome events and/or transposable elements are required to explain the ribosomal gene location diversity in these organisms. The results of the present study corroborate the hypothesis that the A. fasciatus of the Upper Tibagi River region constitute a species complex.

Comparative cytogenetics of Carnegiella marthae and Carnegiella strigata (Characiformes, Gasteropelecidae) and description of a ZZ/ZW sex chromosome system

Comparative cytogenetic analyses of hatchetfishes Carnegiella marthae and Carnegiella strigata (Gasteropelecidae) from the Rio Negro basin were performed using conventional Giemsa staining, silver (Ag) -staining and C-banding. The diploid chromosome numbers of both species equaled 2n = 50 but their karyotypes were distinct. We found evidence for sex chromosomes in C. marthae since karyotype of males presented 20 M + 12 SM + 4 ST + 14 A and ZZ ST chromosomes while the females presented 20 M + 12 SM + 4 ST + 14 A and ZW ST chromosomes of distinct size. Conversely, C. strigata presented 4 M + 4 SM + 2 ST + 40 A chromosomes without sex chromosome heteromorphism. Karyotypes of both species had two NOR-bearing SM chromosomes of distinct size indicating the presence of multiple NOR phenotypes. The sex chromosome pair had specific C-banding pattern allowing identification of both Z and W. This heteromorphic system has previously been described for the gasteropelecids.