Karyotypic characterization of Centromochlus schultzi Rössel 1962 (Auchenipteridae, Centromochlinae) from the Xingu River basin: New inferences on chromosomal evolution in Centromochlus.

Centromochlinae is a widely diverse subfamily with more than 50 species and several taxonomic conflicts due to morphological similarity between Tatia and Centromochlus species. However, cytogenetic studies on this group have been limited to only four species so far. Therefore, here we present the karyotype of Centromochlus schultzi from the Xingu River in Brazil using classic cytogenetic techniques, physical mapping of the 5S and 18S rDNAs, and telomeric sequences (TTAGGG)n. The species had 58 chromosomes, simple NORs and 18S rDNA sites. Heterochromatic regions were detected on the terminal position of most chromosomes, including pericentromeric and centromeric blocks that correspond to interstitial telomeric sites. The 5S rDNA had multiple sites, including a synteny with the 18S rDNA in the pair 24st, which is an ancestral feature for Doradidae, sister group of Auchenipteridae, but appears to be a homoplastic trait in this species. So far, C. schultzi is only the second species within Centromochlus to be karyotyped, but it has already presented characteristics with great potential to assist in future discussions on taxonomic issues in the subfamily Centromochlinae, including the first synteny between rDNAs in Auchenipteridae and also the presence of heterochromatic ITSs that could represent remnants of ancient chromosomal fusions.

Are scattered microsatellites weak chromosomal markers? Guided mapping reveals new insights into Trachelyopterus (Siluriformes: Auchenipteridae) diversity.

The scattered distribution pattern of microsatellites is a challenging problem in fish cytogenetics. This type of array hinders the identification of useful patterns and the comparison between species, often resulting in over-limited interpretations that only label it as "scattered" or "widely distributed". However, several studies have shown that the distribution pattern of microsatellites is non-random. Thus, here we tested whether a scattered microsatellite could have distinct distribution patterns on homeologous chromosomes of closely related species. The clustered sites of 18S and 5S rDNA, U2 snRNA and H3/H4 histone genes were used as a guide to compare the (GATA)n microsatellite distribution pattern on the homeologous chromosomes of six Trachelyopterus species: T. coriaceus and Trachelyopterus aff. galeatus from the Araguaia River basin; T. striatulus, T. galeatus and T. porosus from the Amazonas River basin; and Trachelyopterus aff. coriaceus from the Paraguay River basin. Most species had similar patterns of the (GATA)n microsatellite in the histone genes and 5S rDNA carriers. However, we have found a chromosomal polymorphism of the (GATA)n sequence in the 18S rDNA carriers of Trachelyopterus galeatus, which is in Hard-Weinberg equilibrium and possibly originated through amplification events; and a chromosome polymorphism in Trachelyopterus aff. galeatus, which combined with an inversion polymorphism of the U2 snRNA in the same chromosome pair resulted in six possible cytotypes, which are in Hardy-Weinberg disequilibrium. Therefore, comparing the distribution pattern on homeologous chromosomes across the species, using gene clusters as a guide to identify it, seems to be an effective way to further the analysis of scattered microsatellites in fish cytogenetics.

Identifying fish eggs and larvae: from classic methodologies to DNA metabarcoding.

Studies involving fish eggs and larvae date back to the end of the nineteenth century. Since then, studies with ichthyoplankton have proved to be an essential tool, generating information for the knowledge of the ichthyofauna and the environmental inventory. Most of these studies reveal the difficulty of obtaining a precise taxonomic identification of the collected materials, making research with ichthyoplankton extremely challenging. With the advent of molecular biology, the use of markers such as COI enabled greater taxonomic precision, helping to understand events involving ichthyofauna. Now we can observe the evolution of the molecular identification tool for ichthyoplankton via DNA barcoding, which has been increasingly used over the last few decades. From 2000 to 2010, we found six publications; from 2011 to 2021, 75 papers were published, and in 2022 four studies. Our survey also showed the accuracy of molecular identification when compared to the taxonomic identification of these. In this review, we show the state of the art of studies that used barcode and DNA metabarcoding to identify fish eggs and larvae in different environments and discuss their importance as the best practice for working with these organisms.

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.

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)

Possible Common Origin of B Chromosomes in Neotropical Fish (Siluriformes, Auchenipteridae) Reinforced by Repetitive DNA Mapping

Abstract The aim of this paper was to present the second case of B chromosomes in Auchenipteridae (Trachelyopterus sp.), and to test the hypothesis that the B chromosomes of this species and Parauchenipterus galeatus might have a common origin, since these two species have phylogenetic proximity. Both species have 58 chromosomes in the A complement, heterochromatin preferentially located at terminal region of the most of chromosomes, simple Ag-NORs located at the short arm of a subtelocentric pair, which was confirmed by hybridization with 18S rDNA, two submetacentric pairs carrying 5S rDNA sites, and presence of B chromosomes. The B chromosomes of the two species are small, metacentric, and almost totally heterochromatic, with variation of number intra and interindividual. In addition, for the first time in fish, the telomeric sequence [TTAGGG]n was dispersed along the B chromosomes (both species). The [GATA]n microsatellite were scattered in all chromosomes of the A complement and absent in the B chromosomes, in both species. These aspects confirm the phylogenetic proximity between the genus Parauchenipterus and Trachelyopterus, and they suggest the hypothesis that the B chromosomes of the two species might have common origin, previous to the diversification of these genera.

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 analysis of Centromochlus heckelii (Siluriformes: Auchenipteridae), with a contribution to Centromochlus definition

Historically, there are divergences in the species allocation between Centromochlus and Tatia. This study aimed to generate the first cytogenetic data about Centromochlus and, by analyzing a population of Centromochlus heckelii from the Amazon River basin, to contribute as evidence to a historical taxonomic dilemma. Diploid number of 46 chromosomes and a heteromorphic pair was found in the female karyotypes, thus characterizing a ZZ/ZW sex chromosome system. Pale blocks of heterochromatin were located in centromeric regions of some chromosomes; however, the exclusive female chromosome (W) is almost entirely heterochromatic. AgNORs were detected in terminal position on the short arms of one acrocentric pair in males and two chromosome pairs in females, the acrocentric plus the sex chromosome pair. Notable differences between Centromochlus heckelii and previous data about species of Tatia are: lower diploid number, presence of a sex chromosome system and multiple AgNORs in Centromochlus, while species of Tatia have simple AgNORs and the absence of acrocentric chromosomes. Results in this study show that chromosomal markers could contribute as evidence to taxonomic delimitation studies.(AU)

Historicamente, há divergências na alocação de espécies entre Centromochlus e Tatia. Este estudo teve como objetivo gerar os primeiros dados citogenéticos para Centromochlus e, através da análise de uma população de Centromochlus heckelii da bacia do rio Amazonas, contribuir como evidência para o dilema histórico taxonômico. Foi encontrado o número diploide de 46 cromossomos e um par heteromórfico nos cariótipos das fêmeas, o que caracteriza um sistema sexual ZZ/ZW. Blocos pálidos de heterocromatina foram localizados na região centromérica de alguns cromossomos; no entanto, o cromossomo exclusivo das fêmeas (W) se apresenta quase todo heterocromático. As AgRONs foram detectadas na posição terminal do braço curto de um par acrocêntrico nos machos e em dois pares cromossômicos nas fêmeas, um par de cromossomos acrocêntricos e o par sexual. Notáveis diferenças entre os dados cromossômicos de Centromochlus heckelii e os dados anteriores das espécies de Tatia são: menor número diploide, presença de sistema de cromossomos sexuais e AgRONs múltiplas em Centromochlus, enquanto espécies de Tatia apresentam AgRON simples e ausência de cromossomos acrocêntricos. Resultados deste estudo mostram que marcadores cromossômicos podem contribuir como evidência para estudos de delimitação taxonômica.(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.

First report of B chromosomes in three neotropical thorny catfishes (Siluriformes, Doradidae).

The family Doradidae (Siluriformes) is an important group of fishes endemic to freshwater ecosystems in South America. Some cytogenetic studies have been conducted focused on the group; however, there are no reports on the occurrence of B chromosomes for the family. In this paper the chromosomal characteristics of Platydoras armatulus (Valenciennes, 1840), Pterodoras granulosus (Valenciennes, 1821) and Ossancora punctata (Kner, 1855) were investigated through classical cytogenetics approaches. The conventional staining reveals 2n=58 in Platydoras armatulus and Pterodoras granulosus, however with distinct karyotypic formulae, possibly originated by pericentric inversions. In Ossancora punctata a derivate karyotype was described with 2n=66 and predominance of acrocentric chromosomes. The C banding pattern was resolutive in discriminating the three species, being considered an important cytotaxonomic marker. All species showed B chromosomes totally heterochromatic with non-Mendelian segregation during meiosis and low frequencies in mitotic cells. The probably origin of these additional elements was through fragmentations of chromosomes of the standard complement, which occurred recently and independently in these three species. The diploid number observed in Ossancora punctata is an evidence of centric fusions and up to the moment it is the highest diploid number reported for Doradidae.

Karyotype Diversity and Evolutionary Trends in Armored Catfish Species of the Genus Harttia (Siluriformes: Loricariidae).

Most species of the genus Harttia inhabits the headwaters of small tributaries, but some species are restricted to the main channel of some rivers. This feature, combined with limited dispersal ability, leads to the formation of small isolated populations with reduced gene flow. Currently, there are 23 taxonomically defined and recognized species, and 17 of these are found in Brazil, distributed in several hydrographic basins. Despite this diversity, few chromosomal data for the species belonging to this genus are found in the literature. Thus, this study analyzed, by classical and molecular cytogenetics methodologies, the chromosomal diversity of this genus, to discuss the processes that are involved in the evolution and karyotype differentiation of the species of the group. Seven species of Harttia were analyzed: H. kronei, H. longipinna, H. gracilis, H. punctata, H. loricariformis, H. torrenticola, and H. carvalhoi. The chromosomal diversity found in these species includes different diploid and fundamental numbers, distinct distribution of several repetitive sequences, the presence of supernumerary chromosomes in H. longipinna and multiple sex chromosome systems of the type XX/XY1Y2 in H. carvalhoi and X1X1X2X2/X1X2Y in H. punctata. Lastly, our data highlight the genus Harttia as an excellent model for evolutionary studies.

Chromosome Analyses of Apareiodon argenteus and Apareiodon davisi (Characiformes, Parodontidae): An Extensive Chromosomal Polymorphism of 45S and 5S Ribosomal DNAs.

This study analyzed two Apareiodon species without available chromosome data: Apareiodon argenteus and Apareiodon davisi. Both species have 54 metacentric/submetacentric chromosomes, with centromeric blocks of heterochromatin. Nucleolus organizer regions were active in chromosome pair 2 in A. argenteus and pairs 4 and 9 in A. davisi. In A. argenteus, 45S and 5S ribosomal genes were located in chromosome pairs 2 and 18, respectively. Polymorphisms were observed in these ribosomal sequences in A. davisi, with variations in the number/position of sites, and colocalization of these genes in some chromosome pairs. The WAp repetitive fraction was dispersed along the chromosomes of the two species. The satellite DNA pPh2004 was identified in chromosome pairs 7, 8, 10, 11, and 18 in A. argenteus and in pair 24 in A. davisi. The present study describes the first case of chromosomal polymorphisms involving two ribosomal sequences in Parodontidae and discusses the role of repetitive DNAs in the genome and karyotype diversity of this family.

Occurrence of Natural Hybrids Among Sympatric Karyomorphs in Hoplerythrinus unitaeniatus (Characiformes, Erythrinidae).

In this study, 43 specimens of Hoplerythrinus unitaeniatus from the São Francisco River basin were chromosomally analyzed by conventional Giemsa staining, C-banding, silver nitrate impregnation, and fluorescence in situ hybridization (FISH) with probes of 5S and 18S rDNA. The diploid numbers found were 50 and 52 chromosomes, showing the existence of two well-defined biological entities in sympatry. Specimens with 51 chromosomes, which showed three distinct karyotypic forms, were also found and are characterized as natural hybrids due to the correspondence with the chromosomes of the specimens with 50 and 52 chromosomes. By FISH using 5S and 18S rDNA probes, it was possible to detect specific chromosomal markers for the specimens with 50 and 52 chromosomes, as well as the occurrence of common sites in both. The specimens with 51 chromosomes showed intermediate patterns for these markers, reinforcing the hypothesis that these are actual natural hybrids. A review and new classification for the karyomorphs of H. unitaeniatus have also been proposed.

Basic cytogenetics and physical mapping of 5S and 18S ribosomal genes in Hoplias malabaricus (Osteichthyes, Characiformes, Erythrinidae) from isolated natural lagoons: a conserved karyomorph along the Iguaçu river basin.

Erythrinidae include Neotropical teleost fish that are widely distributed in South America. Hoplias Gill, 1903 include two large groups: H. malabaricus Bloch, 1794 and H. lacerdae Miranda Ribeiro, 1908. Hoplias malabaricus is characterized by remarkable karyotype diversity, with some karyomorphs widely distributed geographically while others are more restricted to certain river basins. Cytogenetic analyzes were performed in a population of Hoplias malabaricus from the Wildlife Refuge of Campos de Palmas, the Iguaçu River basin. The specimens showed diploid number of 42 chromosomes (24m+18sm) without differentiated sex chromosomes system. The impregnation by silver nitrate showed multiple AgNORs. Seven pairs (4, 7, 10, 13, 16, 20 and 21) carrying 18S rDNA were detected by FISH. Heterochromatin was verified in the centromeric and pericentromeric region of most chromosomes and the terminal region of some pairs. FISH with 5S rDNA probes showed two chromosome pairs carrying these sites in the interstitial region (8 and 14). The data obtained in this study are similar to those found for two other populations of H. malabaricus already studied in the basin of the Iguaçu River, confirming the hypothesis that this species is natural, not having been introduced, as well as having an intrinsic characteristic, such as the largest number of sites of 18S rDNA.

Origin of the X1X1X2X2/X1X2Y sex chromosome system of Harttia punctata (Siluriformes, Loricariidae) inferred from chromosome painting and FISH with ribosomal DNA markers.

Harttia is a genus in the subfamily Loricariinae that accommodates fishes popularly known as armored catfishes. They show extensive karyotypic diversity regarding interspecific numerical/structural variation of the karyotypes, with the presence of the XX/XY1Y2 multiple sex chromosome system, as found in H. carvalhoi. In this context, this study aimed to characterize Harttia punctata chromosomally, for the first time, and to infer the rearrangements that originated the X1X1X2X2/X1X2Y multiple sex chromosome system present in this species. The data obtained in this study, with classical (Giemsa, C-banding and AgNORs) and molecular methodologies (fluorescence in situ hybridization) and chromosome microdissection, indicated that a translocation between distinct acrocentric chromosomes bearing rRNA genes, accompanied by deletions in both chromosomes, might have originated the neo-Y chromosome in this species. The data also suggest that the multiple sex chromosome systems present in H. carvalhoi and H. punctata had an independent origin, evidencing the recurrence of chromosome alterations in species from this genus.

Comparative chromosomal analysis and evolutionary considerations concerning two species of genus Tatia (Siluriformes, Auchenipteridae).

Auchenipteridae is divided in two subfamilies, Centromochlinae and Auchenipterinae. Centromochlinae has 31 valid species, from which 13 are included in the genus Tatia Miranda Ribeiro, 1911. Among these, Tatia jaracatia Pavanelli & Bifi, 2009 and Tatia neivai (Ihering, 1930) are the only two representative species from the Paraná-Paraguay basins. This study aimed to analyze cytogenetically these two species and thus provide the first chromosomal data for the genus. Although Tatia jaracatia and Tatia neivai presented 2n=58 chromosomes, some differences were observed in the karyotypic formula. The heterochromatin was dispersed in the centromeric and terminal regions of most chromosomes of Tatia jaracatia, and only in the terminal region of most chromosomes of Tatia neivai. The AgNORs were detected in the subtelocentric pair 28 for both species, which was confirmed by FISH with 18S rDNA probe. The 5S rDNA sites were detected in four chromosome pairs in Tatia jaracatia and three chromosome pairs in Tatia neivai. Both species of Tatia presented great chromosomal similarities among themselves; however, when compared to other species of Auchenipteridae, it was possible to identify some differences in the karyotype macrostructure, in the heterochromatin distribution pattern and in the number and position of 5S rDNA sites, which until now seems to be intrinsic to the genus Tatia.

The role of chromosomal fusion in the karyotypic evolution of the genus Ageneiosus (Siluriformes: Auchenipteridae)

Ageneiosus is the most widely distributed genus of the family Auchenipteridae among South American river basins. Although chromosome studies in the family are scarce, this genus has the largest number of analyzed species, with 2n = 54 to 56 chromosomes, differing from the rest of the family (2n = 58). This study aimed to analyze Ageneiosus inermis from the Araguaia River basin. The diploid number found was of 56 chromosomes. Heterochromatin was allocated in terminal region of most chromosomes, plus a pericentromeric heterochromatic block in pair 1, a pair distinguished by size in relation to other chromosomes pairs. AgNORs were detected in only one submetacentric chromosome pair, which was confirmed by FISH. 5S rDNA was present in only one metacentric chromosome pair. Hybridization with [TTAGGG]n sequence marked the telomeres of all chromosomes, in addition to an ITS in the proximal region of the short arm of pair 1. The repetitive [GATA]n sequence was dispersed, with preferential location in terminal region of the chromosomes. Ageneiosus has a genomic organization somewhat different when compared to other Auchenipteridae species. Evidences indicate that a chromosomal fusion originated the first metacentric chromosome pair in A. inermis, rearrangement which may be a basal event for the genus.

Ageneiosus é o gênero da família Auchenipteridae mais amplamente distribuído em bacias da América do Sul. Apesar dos estudos cromossômicos nesta família serem escassos, este gênero tem o maior número de espécies analisadas, com número diploide variando de 54 a 56 cromossomos, o que difere do restante da família (2n = 58). Este estudo objetivou analisar Ageneiosus inermis da bacia do rio Araguaia. O número diploide encontrado foi de 56 cromossomos. A heterocromatina se mostrou localizada na região terminal da maioria dos cromossomos, além de um bloco heterocromático pericentromérico no par 1, um par facilmente distinguível no cariótipo pelo seu maior tamanho quando comparado aos outros pares do complemento. AgRONs foram detectadas em somente um par de cromossomos submetacêntricos, que foi confirmado pela FISH. 5S rDNA se mostrou presente em somente um par de cromossomos metacêntricos. A hibridização com a sequência [TTAGGG]n marcou os telômeros de todos os cromossomos, além de um ITS (sequência telomérica intersticial) na região proximal do braço curto do par 1. A sequência repetitiva [GATA]n se mostrou dispersa, com localização preferencial na região terminal dos cromossomos. Ageneiosus apresenta uma organização genômica um pouco diferente quando comparada a outras espécies de Auchenipteridae. As evidências indicam que uma fusão cromossômica originou o primeiro par de cromossomos metacêntricos de A. inermis, rearranjo que parece ser um evento basal para o gênero.

A recent transposition of river involving Paraná and São Francisco basins: effects on the genetic variability and structure of the neotropical fish Parauchenipterus galeatus (Siluriformes, Auchenipteridae).

This study analyzed sequences of the control region of mitochondrial DNA (D-loop) in three populations of Parauchenipterus galeatus from the basins of the Paraná, São Francisco, and Piumhi rivers, of which the last river being a region that suffered transposition river. A fragment of 850 base pairs was obtained with a total of 65 polymorphic sites. The data discuss aspects related to the genetic distance between the populations through the phylogenetic reconstruction methods (neighbor-joining, maximum-likelihood, and Bayesian analysis). Moreover, the data suggest that the Piumhi River population (transposition region) has recently gone through a significant bottleneck effect, which must be directly related to the anthropic action that occurred in this region, since the drainage the old existing swamp was necessary for the construction of the transposition channel potentially leading this population in to the current lack of genetic diversity.