Topotype-Based Chromosomal Diversity among Five Species of Freshwater Armored Catfishes in the Hypostomus auroguttatus Supergroup (Actinopterygii: Siluriformes).

Freshwater catfishes from the genus Hypostomus have been models for several cytogenetic studies, due to their intense variability in diploid number, chromosome morphology, and the distribution of repetitive DNAs. Taking into consideration the taxonomic complexity inherent to this group, the present study aims to describe the karyotypes of five species of Hypostomus collected in their type localities: Hypostomus albopunctatus (Regan, 1908), Hypostomus hermanni (Ihering, 1905), Hypostomus iheringii (Regan, 1908), and Hypostomus paulinus (Ihering, 1905) from the Piracicaba River (the Upper Paraná River Basin); and Hypostomus mutucae Knaack, 1999 from the Claro River (the Upper Paraguay River Basin). Our results evidenced a great inter-specific diploid-number variation: 2n = 72 (H. hermanni); 2n = 74 (H. albopunctatus); 2n = 76 (H. paulinus); 2n = 80 (H. iheringii); and 2n = 82 (H. mutucae), which reflects the important role of Robertsonian rearrangements in the karyotypic differentiation among these species. The distribution of heterochromatin also varied considerably among species, making it possible to distinguish each analyzed species, as well as to detect microstructural variations among populations of the same species. These data can support taxonomic revisions when further associated with molecular markers and morphological analyses to delimit, more consistently, the taxonomic status of these Hypostomus species, which have a complex taxonomic diagnosis history.

Karyotype Evolution of Talking Thorny Catfishes Anadoras (Doradidae, Astrodoradinae): A Process Mediated by Structural Rearrangements and Intense Reorganization of Repetitive DNAs.

Anadoras is a thorny catfish genus widespread through the Amazon and Paraguay river basins. It includes 2 nominal species, A. grypus and A. weddellii, plus Anadoras sp. "araguaia," an undescribed species only recognized morphologically. Since Anadoras occupies a basal position within the Astrodoradinae phylogeny, it is crucial to identify its cytogenetic features to comprehend the mechanisms involved in the chromosomal diversification of this subfamily. Therefore, we performed a comparative cytogenetic analysis including all species of Anadoras. Furthermore, we applied a species delimitation analysis based on 600 bp of the mitochondrial cytochrome oxidase subunit 1 (CO1) gene to investigate the taxonomic status of the species. Cytogenetic markers revealed a high degree of similarity among Anadoras weddellii and Anadoras sp. "araguaia," both have 2n = 56 chromosomes (24m + 10sm + 22st/a), single NOR sites on acrocentric pair 28, and 5S rDNA sites on submetacentric pair 15. A. grypus has the most divergent chromosomal characteristics because, even though it also has 2n = 56 chromosomes, it exhibits several differences in the chromosome formula, heterochromatin distribution, and number/position of the rDNA sites. In sum, we believe that the chromosome diversification of Anadoras is due to 4 mechanisms: centric fusion, pericentric/paracentric inversions, nonreciprocal translocations, and activity of transposable elements. Additionally, our phylogenetic tree revealed well-supported clades and, by barcode species delimitation analysis, confirmed the existence of 3 molecular operational taxonomic units, including the putative new species Anadoras sp. "araguaia."

Reconstruction of the Doradinae (Siluriformes-Doradidae) ancestral diploid number and NOR pattern reveals new insights about the karyotypic diversification of the Neotropical thorny catfishes.

Doradinae (Siluriformes: Doradidae) is the most species-rich subfamily among thorny catfishes, encompassing over 77 valid species, found mainly in Amazon and Platina hydrographic basins. Here, we analyzed seven Doradinae species using combined methods (e.g., cytogenetic tools and Mesquite ancestral reconstruction software) in order to scrutinize the processes that mediated the karyotype diversification in this subfamily. Our ancestral reconstruction recovered that 2n=58 chromosomes and simple nucleolar organizer regions (NOR) are ancestral features only for Wertheimerinae and the most clades of Doradinae. Some exceptions were found in Trachydoras paraguayensis (2n=56), Trachydoras steindachneri (2n=60), Ossancora punctata (2n=66) and Platydoras hancockii whose karyotypes showed a multiple NOR system. The large thorny catfishes, such as Pterodoras granulosus, Oxydoras niger and Centrodoras brachiatus share several karyotype features, with subtle variations only regarding their heterochromatin distribution. On the other hand, a remarkable karyotypic variability has been reported in the fimbriate barbells thorny catfishes. These two contrasting karyoevolution trajectories emerged from a complex interaction between chromosome rearrangements (e.g., inversions and Robertsonian translocations) and mechanisms of heterochromatin dispersion. Moreover, we believe that biological features, such as microhabitats preferences, populational size, low vagility and migratory behavior played a key role during the origin and maintenance of chromosome diversity in Doradinae subfamily.

A New Variant B Chromosome in Auchenipteridae: The Role of (GATA)n and (TTAGGG)n Sequences in Understanding the Evolution of Supernumeraries in Trachelyopterus.

Basic and molecular cytogenetic techniques were carried out in 3 Neotropical region populations of catfishes, two of Trachelyopterus galeatus (one from the marshlands of Paraguay River basin and another from Lago Catalão, Amazon River basin) and one of Trachelyopterus porosus, a sympatric population to T. galeatus from the Amazon River basin. This study aimed to describe and understand the structure and evolution of Trachelyopterus B chromosomes, mainly through physical mapping of repetitive elements. A diploid number of 58 chromosomes was found for all individuals, as well as the presence of B chromosomes. For T. porosus this is the first report of a supernumerary. The sympatric species of T. galeatus and T. porosus from Amazon River had 1-3 B chromosomes and T. galeatus from Paraguay River had 1-2 B chromosomes, all of them showed intra- and interindividual numerical variation. Two females of T. porosus exhibited a new variant B chromosome (B2), previously not seen in Auchenipteridae, which might have originated from B1 chromosomes. All B chromosomes were entirely heterochromatic. In contrast to all complement A and B2 chromosomes, in which the telomeric sequences were found in the telomeric regions, B1 chromosomes of all populations were totally marked by (TTAGGG)n probes. (GATA)n sequence sites were found through all complement A chromosomes, but B1 and B2 chromosomes exhibited only a clustered block in one of the chromosome arms. The most frequent B chromosomes (B1) in all populations/species, including those previously studied in Auchenipteridae catfishes, share the following characteristics: totally heterochromatic, small, metacentric, with accumulation of repetitive (TTAGGG)n sequences, and a low number of (GATA)n copies, which might suggest a common ancient origin in Trachelyopterus species/populations.

Contributions to the taxonomy of Trachelyopterus (Siluriformes): comparative cytogenetic analysis in three species of Auchenipteridae

Auchenipteridae is divided into subfamilies Centromochlinae and Auchenipterinae. Parauchenipterus is included in the latter and is subject of taxonomic discussions concerning its validation or synonymization with Trachelyopterus. Herein, three species from two hydrographic basins were cytogenetically analyzed: Parauchenipterus striatulus from Doce River and two sympatric species, P. galeatus and Trachelyopterus coriaceus, from the Araguaia River. Diploid number of 58 chromosomes was verified for all species, but P. striatulus has different karyotype formula from the others. The three species have heterochromatin located in terminal regions of almost all chromosomes and in pericentromeric region on acrocentric chromosomes. Simple NORs was verified on a subtelocentric chromosome for all species. 5S rDNA sites were detected in three submetacentric chromosome pairs in P. striatulus; in a metacentric chromosome pair and submetacentric pair in T. coriaceus; and in one metacentric chromosome pair in P. galeatus. The similarities found in the karyotypes of the three species suggest the existence of only one genus, Trachelyopterus; therefore, our data refutes the validation of Parauchenipterus. Moreover, the differences in 5S rDNA distribution in P. galeatus in comparison with other populations already studied, indicate the existence of a new taxonomic unit, which suggests a species complex in P. galeatus.(AU)

Auchenipteridae é dividida nas subfamílias Centromochlinae e Auchenipterinae. Parauchenipterus encontra-se incluído na última e tem sido alvo de discussões relacionadas com a problemática taxonômica de validação ou sinonimização com Trachelyopterus. Foram analisadas citogeneticamente três espécies de duas bacias hidrográficas: Parauchenipterus striatulus do rio Doce, P. galeatus e Trachelyopterus coriaceus, simpátricas do rio Araguaia. Todas as espécies analisadas apresentaram número diploide de 58 cromossomos, com diferença na fórmula cariotípica de P. striatulus. A heterocromatina foi localizada nas regiões terminais de quase todos os cromossomos e na região pericentromérica nos cromossomos acrocêntricos das três espécies. AgNORs e DNAr 18S detectaram RONs simples em um par de cromossomos subtelocêntricos nas três espécies. DNAr 5S foi detectado em três pares de cromossomos submetacêntricos em P. striatulus; em um par de cromossomos metacêntricos e um par submetacêntrico em T. coriaceus; e em apenas um par de cromossomos metacêntricos em P. galeatus. As semelhanças encontradas nos cariótipos das três espécies analisadas indicam a existência de somente Trachelyopterus (não validação de Parauchenipterus) e a diferença encontrada na distribuição de DNAr 5S de P. galeatus em relação às outras populações já estudadas sugere a existência de uma nova unidade taxonômica, portanto P. galeatus compreende um complexo de espécies.(AU)

Contributions to the taxonomy of Trachelyopterus (Siluriformes): comparative cytogenetic analysis in three species of Auchenipteridae

Auchenipteridae is divided into subfamilies Centromochlinae and Auchenipterinae. Parauchenipterus is included in the latter and is subject of taxonomic discussions concerning its validation or synonymization with Trachelyopterus. Herein, three species from two hydrographic basins were cytogenetically analyzed: Parauchenipterus striatulus from Doce River and two sympatric species, P. galeatus and Trachelyopterus coriaceus, from the Araguaia River. Diploid number of 58 chromosomes was verified for all species, but P. striatulus has different karyotype formula from the others. The three species have heterochromatin located in terminal regions of almost all chromosomes and in pericentromeric region on acrocentric chromosomes. Simple NORs was verified on a subtelocentric chromosome for all species. 5S rDNA sites were detected in three submetacentric chromosome pairs in P. striatulus; in a metacentric chromosome pair and submetacentric pair in T. coriaceus; and in one metacentric chromosome pair in P. galeatus. The similarities found in the karyotypes of the three species suggest the existence of only one genus, Trachelyopterus; therefore, our data refutes the validation of Parauchenipterus. Moreover, the differences in 5S rDNA distribution in P. galeatus in comparison with other populations already studied, indicate the existence of a new taxonomic unit, which suggests a species complex in P. galeatus.(AU)

Auchenipteridae é dividida nas subfamílias Centromochlinae e Auchenipterinae. Parauchenipterus encontra-se incluído na última e tem sido alvo de discussões relacionadas com a problemática taxonômica de validação ou sinonimização com Trachelyopterus. Foram analisadas citogeneticamente três espécies de duas bacias hidrográficas: Parauchenipterus striatulus do rio Doce, P. galeatus e Trachelyopterus coriaceus, simpátricas do rio Araguaia. Todas as espécies analisadas apresentaram número diploide de 58 cromossomos, com diferença na fórmula cariotípica de P. striatulus. A heterocromatina foi localizada nas regiões terminais de quase todos os cromossomos e na região pericentromérica nos cromossomos acrocêntricos das três espécies. AgNORs e DNAr 18S detectaram RONs simples em um par de cromossomos subtelocêntricos nas três espécies. DNAr 5S foi detectado em três pares de cromossomos submetacêntricos em P. striatulus; em um par de cromossomos metacêntricos e um par submetacêntrico em T. coriaceus; e em apenas um par de cromossomos metacêntricos em P. galeatus. As semelhanças encontradas nos cariótipos das três espécies analisadas indicam a existência de somente Trachelyopterus (não validação de Parauchenipterus) e a diferença encontrada na distribuição de DNAr 5S de P. galeatus em relação às outras populações já estudadas sugere a existência de uma nova unidade taxonômica, portanto P. galeatus compreende um complexo de espécies.(AU)

Unrevealing the Karyotypic Evolution and Cytotaxonomy of Armored Catfishes (Loricariinae) with Emphasis in Sturisoma, Loricariichthys, Loricaria, Proloricaria, Pyxiloricaria, and Rineloricaria.

This study provides new insight into the chromosomal diversification in Loricariinae. We analyzed nine species from different Brazilian hydrographic basins, using conventional and molecular cytogenetic methods, aiming to understand the karyotypic diversification, and contribute with cytotaxonomic markers in this group considered one of the most diverse of Loricariidae. Our results evidenced a high karyotypic variability in diploid number (2n) ranging from 2n = 54 (Loricariichthys platymetopon and Loricariichthys anus), 2n = 60 (Rineloricaria reisi and Rineloricaria parva), 2n = 62 (Proloricaria prolixa), 2n = 64 (Loricaria cataphracta complex species), 2n = 66 (Sturisoma barbatum), and 2n = 68 (Pyxiloricaria menezesi). Different patterns of 18S and 5S ribosomal DNA (rDNA) were also identified, while slight divergences in heterochromatin distribution were observed. This high variability is probably related with independent events of Robertsonian translocations, pericentric inversions, and different mechanisms of rDNA sites dispersion (nonreciprocal translocation and transposable element [TEs] co-localization). In addition, our study provides a set of efficient chromosomal markers for the characterization of all analyzed species, and certainly, in future analyzes, will contribute as a useful cytotaxonomic tool in groups where the traditional taxonomy based on morphological data are not sufficient to clarify their relationship.

Chromosomal mapping of repetitive sequences in Hyphessobrycon eques (Characiformes, Characidae): a special case of the spreading of 5S rDNA clusters in a genome.

Cytogenetic data showed a variation in diploid chromosome number in the genus Hyphessobrycon ranging from 2n = 46 to 52, and studies involving repetitive DNA sequences are scarce in representatives of this genus. The purpose of this paper was the chromosomal mapping of repetitive sequences (rDNA, histone genes, U snDNA and microsatellites) and investigation of the amplification of 5S rDNA clusters in the Hyphessobrycon eques genome. Two H. eques populations displayed 2n = 52 chromosomes, with the acrocentric pair No. 24 bearing Ag-NORs corresponding with CMA3+/DAPI-. FISH with a 18S rDNA probe identified the NORs on the short (p) arms of the acrocentric pairs Nos. 22 and 24. The 5S rDNA probe visualized signals on almost all chromosomes in genomes of individuals from both populations (40 signals); FISH with H3 histone probe identified two chromosome pairs, with the pericentromeric location of signals; FISH with a U2 snDNA probe identified one chromosome pair bearing signals, on the interstitial chromosomal region. The mononucleotide (A), dinucleotide (CA) and tetranucleotide (GATA) repeats were observed on the centromeric/pericentromeric and/or terminal positions of all chromosomes, while the trinucleotide (CAG) repeat showed signals on few chromosomes. Molecular analysis of 5S rDNA and non-transcribed spacers (NTS) showed microsatellites (GATA and A repeats) and a fragment of retrotransposon (SINE3/5S-Sauria) inside the sequences. This study expanded the available cytogenetic data for H. eques and demonstrated to the dispersion of the 5S rDNA sequences on almost all chromosomes.

Chromosomal Diversity of Thorny Catfishes (Siluriformes-Doradidae): A Case of Allopatric Speciation Among Wertheimerinae Species of São Francisco and Brazilian Eastern Coastal Drainages.

Wertheimerinae is a small subfamily of thorny catfish composed of two species found in eastern Brazilian coastal drainages: Wertheimeria maculata and Kalyptodoras bahiensis. According to molecular phylogenetic analysis, Franciscodoras marmoratus an endemic species of the São Francisco River is also a member of this subfamily. Even though both phylogenetic approaches suggest that this group is one of the oldest lineages of the Doradidae, a disagreement remains about the constitution of Wertheimerinae. Hence, cytogenetic analysis is important to understand the karyotypic evolution of thorny catfish and can be a useful cytotaxonomic tool to clarify the relationships between these species. All Wertheimerinae species, and F. marmoratus here analyzed, shared 2n = 58 chromosomes, karyotypic formulas (24m+12sm +8st +14a), and nucleolus organizer region (NOR) pattern (terminal 18S rDNA sites on pair 22). Differences were noted in heterochromatin and 5S rDNA site distribution. The chromosomal markers here applied added to the molecular data, reinforcing that these three species actually represent a well-resolved taxonomic unit. Our results represent one more evidence of the ancient connectivity between eastern coastal drainages and São Francisco River, whose separation represented an important event for the allopatric speciation that produced the current forms of Wertheimerinae subfamily.

First chromosomal analysis of Gymnorhamphichthys britskii: the remarkable lowest diploid value within the family Rhamphichthyidae (Gymnotiformes)

Gymnorhamphichthys britskii is a Neotropical electric fish of family Rhamphichthyidae described from the Paraná-Paraguay system. This study reports the first karyotypic description of G. britskii collected from the upper Paraná river basin, which presented 2n=38 chromosomes, karyotype composed of 14 metacentric, 8 submetacentric, 2 subtelocentric and 14 acrocentric chromosomes, and fundamental number as 62 for both sexes. Heteromorphic sex chromosomes were absent. A single pair of nucleolar organizing regions (NORs) was detected in the submetacentric chromosome pair number 9 by silver staining and confirmed by the 18S rDNA probe. The 5S rDNA was located in a single chromosome pair. Heterochromatic regions were clearly observed in the short arms of the NOR-bearing chromosome pair and in the telomeric positions of most acrocentric chromosomes. Besides the present data are valuable to help in understanding karyotypic evolution in Rhamphichthyidae, data from NORs confirmed the tendency of this family in presenting simple NORs sites, similar to the other Gymnotiformes clades. Yet, the presence of a large heterochromatic block in the NOR-bearing chromosome can be used as cytogenetic markers for G. britskii, and that centric fusions appear to be an important mechanism in the karyotype evolution and differentiation among Gymnotiformes species.(AU)

Gymnorhamphichthys britskii é um peixe neotropical da família Rhamphichthyidae descrita no sistema Paraná-Paraguai. Este estudo relata a primeira descrição cariotípica de G. britskii coletado na bacia do alto rio Paraná, que apresentou 2n = 38 cromossomos, cariótipo composto por 14 metacêntricos, 8 submetacêntricos, 2 subtelocêntricos e 14 acrocêntricos, e número fundamental 62 para ambos sexos. Cromossomos sexuais heteromórficos estavam ausentes. Um único par de regiões organizadoras de nucléolos (RONs) foi detectado no par de cromossomos submetacêntricos número 9 por coloração com prata e confirmado pela sonda DNAr 18S. O DNAr 5S foi localizado em um único par cromossômico. Regiões heterocromáticas foram claramente observadas nos braços curtos do par de cromossomos que carrega a RON e nas posições teloméricas da maioria dos cromossomos acrocêntricos. Além dos dados presentes serem valiosos para auxiliar na compreensão da evolução cariotípica em Rhamphichthyidae, dados de RONs confirmaram a tendência desta família em apresentar sítios simples de RONs, semelhantes aos demais clados de Gymnotiformes. No entanto, a presença de um grande bloco heterocromático no cromossomo portador da RON, pode ser usado como marcador citogenético para G. britskii e as fusões cêntricas parecem ser um mecanismo importante na evolução e diferenciação cariotípica entre as espécies de Gymnotiformes.(AU)

First chromosomal analysis of Gymnorhamphichthys britskii: the remarkable lowest diploid value within the family Rhamphichthyidae (Gymnotiformes)

Gymnorhamphichthys britskii is a Neotropical electric fish of family Rhamphichthyidae described from the Paraná-Paraguay system. This study reports the first karyotypic description of G. britskii collected from the upper Paraná river basin, which presented 2n=38 chromosomes, karyotype composed of 14 metacentric, 8 submetacentric, 2 subtelocentric and 14 acrocentric chromosomes, and fundamental number as 62 for both sexes. Heteromorphic sex chromosomes were absent. A single pair of nucleolar organizing regions (NORs) was detected in the submetacentric chromosome pair number 9 by silver staining and confirmed by the 18S rDNA probe. The 5S rDNA was located in a single chromosome pair. Heterochromatic regions were clearly observed in the short arms of the NOR-bearing chromosome pair and in the telomeric positions of most acrocentric chromosomes. Besides the present data are valuable to help in understanding karyotypic evolution in Rhamphichthyidae, data from NORs confirmed the tendency of this family in presenting simple NORs sites, similar to the other Gymnotiformes clades. Yet, the presence of a large heterochromatic block in the NOR-bearing chromosome can be used as cytogenetic markers for G. britskii, and that centric fusions appear to be an important mechanism in the karyotype evolution and differentiation among Gymnotiformes species.(AU)

Gymnorhamphichthys britskii é um peixe neotropical da família Rhamphichthyidae descrita no sistema Paraná-Paraguai. Este estudo relata a primeira descrição cariotípica de G. britskii coletado na bacia do alto rio Paraná, que apresentou 2n = 38 cromossomos, cariótipo composto por 14 metacêntricos, 8 submetacêntricos, 2 subtelocêntricos e 14 acrocêntricos, e número fundamental 62 para ambos sexos. Cromossomos sexuais heteromórficos estavam ausentes. Um único par de regiões organizadoras de nucléolos (RONs) foi detectado no par de cromossomos submetacêntricos número 9 por coloração com prata e confirmado pela sonda DNAr 18S. O DNAr 5S foi localizado em um único par cromossômico. Regiões heterocromáticas foram claramente observadas nos braços curtos do par de cromossomos que carrega a RON e nas posições teloméricas da maioria dos cromossomos acrocêntricos. Além dos dados presentes serem valiosos para auxiliar na compreensão da evolução cariotípica em Rhamphichthyidae, dados de RONs confirmaram a tendência desta família em apresentar sítios simples de RONs, semelhantes aos demais clados de Gymnotiformes. No entanto, a presença de um grande bloco heterocromático no cromossomo portador da RON, pode ser usado como marcador citogenético para G. britskii e as fusões cêntricas parecem ser um mecanismo importante na evolução e diferenciação cariotípica entre as espécies de Gymnotiformes.(AU)

Comparative Cytogenetics Analysis on Five Genera of Thorny Catfish (Siluriformes, Doradidae): Chromosome Review in the Family and Inferences About Chromosomal Evolution Integrated with Phylogenetic Proposals.

Doradidae has been a target of phylogenetic studies over the last few years, but chromosomal information about the family is still scarce. Therefore, new cytogenetic data are provided herein and they are correlated with phylogenetic proposals to contribute to the knowledge of chromosomal evolution within doradids. Cytogenetic studies were performed on Trachydoras paraguayensis, Anadoras sp. "araguaia," Ossancora eigenmanni, Platydoras armatulus, and Rhinodoras dorbignyi. O. eigenmanni, P. armatulus, and R. dorbignyi had 2n = 58 chromosomes as found for most doradids, but T. paraguayensis and Anadoras sp. "araguaia" had 2n = 56 chromosomes, probably caused by a chromosomal reduction. There is a great maintenance of 2n = 58 verified in doradids, but karyotype formulas are diverse. Moreover, other markers (i.e., nucleolar organizer regions, heterochromatin distribution, and 5S and 18S rDNA) showed a great diversity among the analyzed species. Contrasting the variability in the chromosomal markers with the maintenance of diploid number, it is likely that inversions and translocations played an important role in chromosome differentiation in Doradidae. Herein, we created an integrative discussion linking cytogenetic data to phylogenetic proposals, based on morphological and genetic features, enabling us to identify possible cytogenetic traits, as well as probable chromosomal plesiomorphy and apomorphy of Doradidae species.

Chromosomal Diversity of Three Species of Hypostomus Lacépède, 1803 (Siluriformes, Loricariidae), from the Paraná River Basin, Brazil: A Species Complex in Hypostomus ancistroides Reinforced by a ZZ/ZW Sex Chromosome System.

Hypostomus shows wide morphological patterns, corroborated by great chromosomal diversity that has suggested the existence of new species, especially from small tributaries. Cytogenetic analysis has contributed to estimate a cryptic diversity providing important data for taxonomic and evolutionary studies. Cytogenetic techniques were carried out on species from a small tributary of Ivaí River, Keller River (upper Paraná River basin): Hypostomus aff. ancistroides, Hypostomus topavae, and Hypostomus aff. hermanni that presented 2n = 68, 80, and 72 chromosomes, respectively. Each species showed the same diploid number from previous descriptions for other populations but different karyotype formulas, and Hypostomus aff. ancistroides had a ZZ/ZW sex chromosome system. Multiple NORs (nucleolar organizer regions) and pericentromeric heterochromatin blocks were found in the three species. Moreover, each of them showed species-specific heterochromatins. Multiple 5S rDNA sites were detected in Hypostomus aff. ancistroides and H. topavae, whereas Hypostomus aff. hermanni had only one pair bearing these sites. In addition to the divergence in the karyotype formulas, chromosomal markers used showed karyotype differences in the three species related to other respective populations studied. Furthermore, the first description of a ZZ/ZW system for Hypostomus aff. ancistroides reinforces the hypothesis that it may correspond to a species complex and yet, confirming an unknown cryptic diversity existent in small rivers.

Comparative Cytogenetics of the Black Ghost Knifefish (Gymnotiformes: Apteronotidae): Evidence of Chromosomal Fusion and Pericentric Inversions in Karyotypes of Two Apteronotus Species.

The karyotype and chromosomal characteristics of Apteronotus albifrons and Apteronotus caudimaculosus collected from populations of two different large Brazilian river basins were analyzed by conventional and molecular cytogenetic techniques, to contribute to the differentiation and identification of the species in this genus. The diploid chromosome number was 2n = 24 for A. albifrons, but with difference in the karyotype structure and fundamental number values between two populations under study. In A. caudimaculosus, the diploid chromosome number was 2n = 26, which was classified as 22 metacentric (m), 2 submetacentric (sm), and 2 acrocentric (a) chromosomes. Heterochromatins were preferentially located in pericentromeric regions for both species. However, there are more C-banded chromosomes in A. caudimaculosus than A. albifrons. The sites of 18S DNA as revealed by fluorescence in situ hybridization (FISH) in the karyotypes of both species corresponded to sites revealed by Ag impregnation, although some additional 18S rDNA sites were observed in the genome of A. caudimaculosus. FISH with 5S rDNA-probe revealed interstitial sites on the m pair No. 1 for individuals of both A. albifrons populations, and in pericentromeric regions on the long arm of pair Nos. 5 and 9 in those of A. caudimaculosus. The karyotypes of A. albifrons and A. caudimaculosus indicated a reduction of 2n resulting from chromosomal fusion, as could be hypothesized from the presence of an interstitial telomere sequence in two chromosome pairs in karyotype of A. caudimaculosus. Thus, the present study demonstrated species-specific cytogenetic markers of otherwise morphologically very similar species A. albifrons and A. caudimaculosus.

Cytogenetics of Gymnogeophagus setequedas (Cichlidae: Geophaginae), with comments on its geographical distribution

We provide cytogenetic data for the threatened species Gymnogeophagus setequedas, and the first record of that species collected in the Iguaçu River, within the Iguaçu National Park's area of environmental preservation, which is an unexpected occurrence for that species. We verified a diploid number of 2n = 48 chromosomes (4sm + 24st + 20a) and the presence of heterochromatin in centromeric and pericentromeric regions, which are conserved characters in the Geophagini. The multiple nucleolar organizer regions observed in G. setequedas are considered to be apomorphic characters in the Geophagini, whereas the simple 5S rDNA cistrons located interstitially on the long arm of subtelocentric chromosomes represent a plesiomorphic character. Because G. setequedas is a threatened species that occurs in lotic waters, we recommend the maintenance of undammed environments within its known area of distribution.(AU)

Fornecemos dados citogenéticos para a espécie ameaçada Gymnogeophagus setequedas, e o primeiro registro da espécie coletado no rio Iguaçu, na área de preservação ambiental do Parque Nacional do Iguaçu, a qual é uma área de ocorrência inesperada para esta espécie. Verificamos em G. setequedas 2n = 48 cromossomos (4sm + 24st + 20a) e heterocromatina presente nas regiões centroméricas e pericentroméricas, as quais indicam caracteres conservados em Geophagini. Múltiplas regiões organizadoras de nucléolos foram observadas em G. setequedas e são consideradas características apomórficas em Geophagini, enquanto cístrons de DNAr 5S simples e localizados intersticialmente no braço longo de cromossomos subtelocêntricos representam uma característica plesiomórfica. Visto que G. setequedas é uma espécie ameaçada de extinção que ocorre em águas lóticas, recomendamos a manutenção de ambientes livre de barragens em sua área de distribuição.(AU)

Cytogenetics of Gymnogeophagus setequedas (Cichlidae: Geophaginae), with comments on its geographical distribution

We provide cytogenetic data for the threatened species Gymnogeophagus setequedas, and the first record of that species collected in the Iguaçu River, within the Iguaçu National Park's area of environmental preservation, which is an unexpected occurrence for that species. We verified a diploid number of 2n = 48 chromosomes (4sm + 24st + 20a) and the presence of heterochromatin in centromeric and pericentromeric regions, which are conserved characters in the Geophagini. The multiple nucleolar organizer regions observed in G. setequedas are considered to be apomorphic characters in the Geophagini, whereas the simple 5S rDNA cistrons located interstitially on the long arm of subtelocentric chromosomes represent a plesiomorphic character. Because G. setequedas is a threatened species that occurs in lotic waters, we recommend the maintenance of undammed environments within its known area of distribution.(AU)

Fornecemos dados citogenéticos para a espécie ameaçada Gymnogeophagus setequedas, e o primeiro registro da espécie coletado no rio Iguaçu, na área de preservação ambiental do Parque Nacional do Iguaçu, a qual é uma área de ocorrência inesperada para esta espécie. Verificamos em G. setequedas 2n = 48 cromossomos (4sm + 24st + 20a) e heterocromatina presente nas regiões centroméricas e pericentroméricas, as quais indicam caracteres conservados em Geophagini. Múltiplas regiões organizadoras de nucléolos foram observadas em G. setequedas e são consideradas características apomórficas em Geophagini, enquanto cístrons de DNAr 5S simples e localizados intersticialmente no braço longo de cromossomos subtelocêntricos representam uma característica plesiomórfica. Visto que G. setequedas é uma espécie ameaçada de extinção que ocorre em águas lóticas, recomendamos a manutenção de ambientes livre de barragens em sua área de distribuição.(AU)

Cytogenetics of the Thorny Catfish Trachydoras paraguayensis (Eigenmann & Ward, 1907), (Siluriformes, Doradidae): Evidence of Pericentric Inversions and Chromosomal Fusion.

The karyotype and chromosomal characteristics of Trachydorasparaguayensis, a representative of the South American catfish family Doradidae, were analyzed by conventional (Giemsa staining, silver staining, C-banding) and molecular (FISH with rDNA and telomeric probes) cytogenetic techniques. The diploid chromosome number was 2n = 56, with 36 metacentric, 16 submetacentric, and 4 subtelocentric chromosomes in both sexes; however, a remarkable heteromorphism in pair 22 (submetacentric and metacentric elements) was detected in 6 individuals. Compared to other representatives of Doradidae which mostly have 58 chromosomes, the karyotype of T. paraguayensis suggests a reduction in 2n due to chromosomal fusion, as could be deduced from the presence of an interstitial telomere sequence in the submetacentric pair 19. Pale heterochromatic blocks were present in the terminal regions of some chromosomes, very similar to other species of Doradidae. The interstitial position of the NORs observed in the karyotype of T. paraguayensis differs from those reported for most Doradidae species, indicating that it is a derived character. FISH with 5S rDNA revealed 2 interstitial fluorescent signals in the submetacentric pair 22, and the polymorphism of these sites likely resulted from a pericentric inversion.

An uncommon co-localization of rDNA 5S with major rDNA clusters in Callichthyidae (Siluriformes): a report case in Corydoras carlae Nijssen & Isbrücker, 1983.

Corydoras Lacepède, 1803 is the most specious genus of Corydoradinae subfamily and many of its species are still unknown in relation to molecular cytogenetic markers. However, the diploid number and karyotypic formula were recorded for many species of this group. In current study, we provided the first cytogenetic information of Corydoras carlae Nijssen & Isbrücker, 1983, an endemic fish species from Iguassu River basin, Paraná State, Brazil. The individuals were collected in Florido River, a tributary of Iguassu River and analysed with respect to diploid number, heterochromatin distribution pattern, Ag-NORs and mapping of 5S and 18S ribosomal genes. The karyotype of this species comprises 46 chromosomes arranged in 22m+22sm+2st. The heterochromatin is distributed in centromeric and pericentromeric positions in most of the chromosomes, and also associated with NORs. The Ag-NORs were detected in the terminal position on the long arm of the metacentric pair 6. The double-FISH technique showed that 5S rDNA and 18S rDNA were co-localized in the terminal portion on the long arm of the metacentric pair 6. This condition of co-localization of ribosomal genes in Corydoras carlae seems to represent a marker for this species.

Basic cytogenetics and physical mapping of ribosomal genes in four Astyanax species (Characiformes, Characidae) collected in Middle Paraná River, Iguassu National Park: considerations on taxonomy and systematics of the genus.

Karyotypes and chromosomal characteristics of both minor and major rDNAs in four fish species known popularly as "lambaris", namely Astyanaxabramis (Jenyns, 1842), Astyanaxasuncionensis Géry, 1972, Astyanaxcorrentinus (Holmberg, 1891) and Astyanax sp. collected from downstream of the Iguassu Falls (Middle Paraná River basin), preservation area of the Iguassu National Park, were analyzed by conventional and molecular protocols. Astyanaxabramis had diploid chromosome number 2n=50 (4m+30sm+8st+8a) and single AgNORs (pair 22), Astyanaxasuncionensis had 2n=50 (8m+24sm+6st+12a) and single AgNORs (pair 20), Astyanax sp. had 2n=50 (4m+26sm+8st+12a) and single AgNORs (pair 25), and Astyanaxcorrentinus had 2n=36 (12m+16sm+2st+6a) and multiple AgNORs (pairs 12, 15, 16, 17). FISH with 18S rDNA showed a single site for Astyanaxabramis, Astyanaxasuncionensis and Astyanax sp. and multiple for Astyanaxcorrentinus (14 sites). FISH with 5S rDNA showed single 5S-bearing loci chromosome pair only for Astyanaxasuncionensis and multiple for Astyanaxabramis (four sites), Astyanaxcorrentinus (five sites) and Astyanax sp. (four sites). Distinct distribution patterns of heterochromatin were observed for karyotypes of all species, with the exception of the first acrocentric chromosome pair characterized by centromeric, interstitial-proximal and telomeric blocks of heterochromatin on the long arm, which may represent homeology between karyotypes of Astyanaxabramis and Astyanaxasuncionensis. Our study showed species-specific characteristics which can serve in diagnosis and differentiation between Astyanaxabramis and Astyanaxasuncionensis, considered cryptic species, as well as strengthening the occurrence of a species of Astyanax not yet described taxonomically. In addition, the data obtained from first cytogenetic studies in Astyanaxcorrentinus suggest a high similarity with Astyanaxschubarti Britski, 1964, suggesting that these species may belong to the same morphological group and that can be phylogenetically related.

Heterochromatin polymorphism and physical mapping of 5S and 18S ribosomal DNA in four populations of Hypostomus strigaticeps (Regan, 1907) from the Paraná River basin, Brazil: evolutionary and environmental correlation.

A cytogenetic analysis was performed on four populations of Hypostomus strigaticeps from the Paraná River basin, Brazil. Two populations were collected from the large channel river at the Itaipu reservoir area and the other two were from the upper stretches of tributaries of the Paraná River. All populations showed 2n=72 chromosomes (12m+12sm+18st+30a), intra- and interpopulation 18S rDNA site polymorphisms (two to three acrocentric chromosome pairs), and multiple 5S rDNA sites in three chromosome pairs (4, 21, and 28). C-banding revealed heterochromatin located in the centromere and pericentromere regions of most chromosome; however, large heterochromatic blocks (CMA3(-)/DAPI(+)) on the long arm of acrocentric chromosomes identified intra- and interpopulation polymorphism. The amount and distribution of heterochromatin seem to be correlated to biogeographical characteristics of H. strigaticeps along the Paraná River. Morphometric results also showed diversity among the populations, suggesting phenotypic plasticity of this species. Evolutionary, taxonomy, and biogeographical approaches with regard to H. strigaticeps and interrelationships in Hypostomus are discussed.