Mapping of the 18S and 5S ribosomal RNA genes in the fish Prochilodus argenteus Agassiz, 1829 (Characiformes, Prochilodontidae)

Cytogenetic Trends in Two Families of the Neotropical Catfishes: Heptapteridae and Pseudopimelodidae (Siluriformes)

Several neotropical Siluriformes groups suffered important taxonomic revisions based on the evaluation of morphological and molecular characteristics that allow the construction of new phylogenetic hypothesis. In the present study were cytogenetically analyzed six species belonging to Heptapteridae (Cetopsorhamdia iheringi, Phenacorhamdia tenebrosa, Rhamdella eriarcha, Pimelodella meeki, Pimelodella australis, Heptapterus mustelinus) and two to Pseudopimelodidae families (Microglanis cottoides and Microglanis cibelae) by means of differential staining techniques to describe more precisely cytogenetic similarities and differences. The diploid number of R. eriarcha with 2n = 58 and M. cibelae with 2n = 56 were reported for the first time. Also, the lowest chromosome number (2n = 48) for P. tenebrosa was described. The chromosome-banding techniques for to put in evidence nucleolar organizers impregnated by silver nitrate ([AgNORs], chromomycin A₃ [CMA₃], and rDNA 18S) showed for all studied species conserved patterns, characteristic for each family. The rDNA 5S showed high variability among species or populations of both families, these regions could be simple or multiple, syntenic, or not with rDNA18S. The chromosome markers showed that both families are related not only from a morphologic point of view but also by their karyotypic characteristics, however, some of the present cytogenetic results evidence the importance of new morphologic, molecular, and phylogenetic studies to improve the knowledge of these fish groups.

Contributions to the systematic of Pimelodidae (Osteichthyes, Siluriformes): basic and molecular cytogenetics on seven species of Pimelodus from three Brazilian hydrographic systems

ABSTRACT Pimelodidae harbors several species and is widely distributed throughout the Neotropical region. Pimelodus is the genus with the largest number of species, however it is a polyphyletic group. Cytogenetic analyzes of the valid species still covers less than half of them. Herein, seven Pimelodus species from three Brazilian hydrographic systems were analyzed through basic (Giemsa, AgNORs and C banding) and molecular (5S and 18S rDNA-FISH) cytogenetic methods. All species had 2n=56 chromosomes with different karyotype formulas observed among the species. AgNORs were corresponding to 18S rDNA and localized on long arm of one chromosome pair in all species. Heterochromatin distribution follows the pattern commonly verified in the family and allows to identify each one of the studied species. 5S rDNA marker was interspecifically variable in number and position of cistrons. Pimelodus ortmanni had B chromosomes varying intra and inter-individually. We performed a discussion on our own and available cytogenetic data for Pimelodidae, and the associating of them with available phylogeny enable us identifying features that distinguish subgroups within Pimelodidae, such as NORs location (terminal/long arm for species belonging to “Iheringichthys-Parapimelodus” and “Pimelodus maculatus” subclades) and location of 5S rDNA sites (pericentromeric/interstitial/ long arm for species belonging to Pimelodus group).

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 Mapping of Repeat DNA in Bergiaria westermanni (Pimelodidae, Siluriformes): Localization of 45S rDNA in B Chromosomes

The occurrence of repetitive DNA in autosomes and B chromosomes of Bergiaria westermanni was examined using conventional and molecular cytogenetic techniques. This species exhibited 2n = 56 chromosomes, with intra- and interindividual variation in the number of heterochromatic B chromosomes (from 0 to 4). The 5S rDNA was localized in pairs 1 and 5, and histone probes (H1, H3, and H4) and U2 small nuclear RNA were syntenic with 5S rDNA in pair 5. Histone sequences were also located in chromosome pair 14. The (GATA)n sequence was dispersed throughout the autosomes and B chromosomes, with clusters (microsatellite accumulation) in some chromosome regions. The telomeric probe revealed no signs of chromosomal rearrangements in the genome of B. westermanni. The 45S rDNA sites were detected in the terminal region of pair 27; these sites corresponded to a GC-rich heterochromatin block. In addition, 3 of the 4 B chromosomes also contained 45S rDNA copies. Silver nitrate staining in interphase nuclei provided indirect evidence of the expression of these rRNA genes in B chromosomes, indicating the probable origin of these elements. This report shows plasticity in the chromosomal localization of repeat DNA in B. westermanni and features a discussion of genomic diversification.

Studies in two allopatric populations of Hypostomus affinis (Steindachner, 1877): the role of mapping the ribosomal genes to understand the chromosome evolution of the group

Several cytogenetic markers show chromosomal diversity in the fish such as "armoured catfish". Although studies have characterized many species in the major genera representing these Siluridae, particularly in the genus Hypostomus Lacépède, 1803, trends in chromosome evolution of this group remain unclear. The Paraíba do Sul river basin contains the armoured catfish Hypostomus affinis Steindachner, 1877, which is unique because of its distribution of repetitive DNAs, the 5S and 18S rDNA. Identified samples and registered collections in Brazilian museums were identified as the same typological species, while we observed wide variations in the physical location of this gene in the karyotype based on fluorescent in situ hybridization results. In this study, we propose that these species can represent evolutionarily independent units, as these fish frequently undergo processes such as dispersion and vicariance and that the rDNA is associated with DNA that spreads in the genome, such as transposons. Additionally, the absence of gene flow due to the distance of the sample location could intensify evolutionary processes. The phenotypes found for the 18S rDNA showed minor changes in relation to the number of sites between the lower and upper drainage regions of Paraíba do Sul. The large difference in the number of sites found for the 5S rDNA entered the same region (upper drainage of the basin) and the literature data could represent a population dynamics where an expansion of the 5S rDNA sites provides an extinct or non-sampled cytotype in this work.

Hidden Diversity in the Populations of the Armored Catfish Ancistrus Kner, 1854 (Loricariidae, Hypostominae) from the Paraná River Basin Revealed by Molecular and Cytogenetic Data

Only one species of armored catfish, Ancistrus cirrhosus Valenciennes 1836, has been historically described in the basin of the Paraná River, from Misiones (Argentina). However, the ample variation found in the morphology and coloration of the populations sampled in the tributaries of the Brazilian state of Paraná makes it difficult to establish the real taxonomic status and evolutionary history of the Ancistrus specimens, suggesting that A. cirrhosus is not the only species found in this basin. By combining data on mitochondrial DNA (COI gene) and chromosomal markers from different Ancistrus populations, totaling 144 specimens, in the tributaries of the Paraná, and specimens from Misiones (type-locality of A. cirrhosus), we detected five distinct evolutionary lineages. All the specimens were 2n = 50, but had four distinct karyotype formulae. The results of the Generalized Mixed Yule Coalescent (GYMC) and the genetic distances (uncorrected P-values) between lineages ranged from 3 to 5%. Clusters of 18S rDNA were observed in a single chromosome pair in seven populations of Ancistrus, but at different positions, in some cases, in synteny with the 5S rDNA sites. Multiple 5S sites were observed in all populations. Overall, the cytogenetic data reinforce the genetic evidence of the diversification of lineages, and indicate the existence of candidate species in the study region. The evidence indicates that at least four candidate species of the Ancistrus may coexist in the Paraná basin besides A. cirrhosus. Overall, our results provide a comprehensive scenario for the genetic variation among Ancistrus populations and reinforce the conclusion that the true diversity of the freshwater fish of the Neotropical regions has been underestimated.

An Unusual Accumulation of Ribosomal Multigene Families and Microsatellite DNAs in the XX/XY Sex Chromosome System in the Trans-Andean Catfish Pimelodella cf. chagresi (Siluriformes:Heptapteridae)

This work constitutes the first cytogenetic characterization of a trans-Andean species of Heptapteridae. The catfish Pimelodella cf. chagresi from the Upper Rio Magdalena was studied, applying standard cytogenetic techniques (Giemsa, C-banding, and argyrophilic nucleolar organizer region [Ag-NOR]) and fluorescence in situ hybridization techniques using repetitive DNA probes: microsatellites (CA₁₅ and GA₁₅) and ribosomal RNA (rRNA) multigene families (18S and 5S recombinant DNA [rDNA] probes). The species showed a unique diploid chromosome number 2n = 50 (32m [metacentrics] +14sm [submetacentrics] +4st [subtelocentrics]) and a XX/XY sex chromosomal system, where the heteromorphic Y-chromosome revealed a conspicuous accumulation of all the assayed domains of repetitive DNA. P. cf. chagresi karyotype shares common features with other Heptapteridae, such as the predominance of metacentric and submetacentric chromosomes, and one pair of subtelomeric nucleolar organizer regions (NORs). These results reflect an independent karyological identity of a trans-Andean species and the relevance of repetitive DNA sequences in the process of sex chromosome differentiation in fish; it is the first case of syntenic accumulation of rRNA multigene families (18S and 5S rDNA) and microsatellite sequences (CA₁₅ and GA₁₅) in a differentiated sex chromosome in Neotropical fish.

Cytogenetics of Two Onychostoma Species in Taiwan by Ag-NOR and 18S rDNA Profiles

Chiao-Chuan Han, Tsair-Bor Yen, Nian-Cih Chen, and Mei-Chen Tseng (2017) Both Onychostoma barbatulum and O. alticorpus are primary freshwater fish in Taiwan. The former has been developed as an aquaculture species with high economic value, while the latter is a native endemic species in Taiwan. Understanding the cytogenetic information of these two species is necessary for their selected breeding, recovery, and management. In this study, Giemsa staining, silver-binding nucleolar organizer region (Ag-NOR), C-banding, and fluorescence in situ hybridization (FISH) with 18S ribosomal (r)DNA probes were used to analyze the cytogenetic characteristics. Results of Giemsa staining showed that the two Onychostoma species shared the same number of chromosomes, 2n = 50. Respective karyotype formulas of the female and male were 10 m + 22 sm + 10 st + 8 t and 11 m + 22 sm + 10 st + 7 t in O. barbatulum, and 14 m + 18 sm + 8 st + 10 t and 15 m + 18 sm + 8 st + 9 t in O. alticorpus. Karyotypes of both species showed a pair of heteromorphic chromosomes in male fish. Their sex determination should be the XX/XY system. Two pairs of Ag-NORs were found in O. barbatulum, but only one pair occurred in O. alticorpus. C-banding areas were observed on centromeres or telomeres of some chromosomes. FISH revealed different cytogenetic characters between these two species. The above cytogenetic information will contribute to species identification, population recovery, and advantages for breeding and management in the future.

Repetitive DNA in the Catfish Genome: rDNA, Microsatellites, and Tc1-Mariner Transposon Sequences in Imparfinis Species (Siluriformes, Heptapteridae)

Physical mapping of repetitive DNA families in the karyotypes of fish is important to understand the organization and evolution of different orders, families, genera, or species. Fish in the genus Imparfinis show diverse karyotypes with various diploid numbers and ribosomal DNA (rDNA) locations. Here we isolated and characterized Tc1-mariner nucleotide sequences from Imparfinis schubarti, and mapped their locations together with 18S rDNA, 5S rDNA, and microsatellite probes in Imparfinis borodini and I. schubarti chromosomes. The physical mapping of Tc1/Mariner on chromosomes revealed dispersed signals in heterochromatin blocks with small accumulations in the terminal and interstitial regions of I. borodini and I. schubarti. Tc1/Mariner was coincident with rDNA chromosomes sites in both species, suggesting that this transposable element may have participated in the dispersion and evolution of these sequences in the fish genome. Our analysis suggests that different transposons and microsatellites have accumulated in the I. borodini and I. schubarti genomes and that the distribution patterns of these elements may be related to karyotype evolution within Imparfinis.

Gymnotus coatesi (Gymnotiformes): A Case of Colocation of Multiple Sites of 18S rDNA with Telomeric Sequences

Gymnotus coatesi is a small and rare species of banded knife fish that was originally described by LaMonte in 1935, found along the main stretch of the Amazon River. There is no described cytogenetic data on this species. We analyzed the karyotype of five specimens of G. coatesi collected from Cururutuia Stream in Bragança, Pará, Brazil. The obtained diploid number is 50 and the karyotypic formula is 24 m/sm +26 st/a. The constitutive heterochromatin is DAPI positive and distributed mainly in the centromeric and pericentromeric regions of the chromosomes. Ag-nucleolus organizer regions staining showed nine active sites. The 5S rDNA probe hybridized chromosome pair 17 in the interstitial part of the long arm. Fluorescence in situ hybridization (FISH) with telomeric probes revealed signals only at terminal regions of the chromosomes. The 18S rDNA probe hybridized to 21 sites, and these signals colocalized with the telomeric sequences. This relatively high number of 18S rDNA sites may reflect gene duplication mediated by transposable elements. These results indicate that although the diploid number of G. coatesi is within the range previously observed for other members of the genus, various karyotypic characteristics distinguish G. coatesi from the other species of the genus and members of the Gymnotiform order.

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.

Highest Diploid Number Among Gymnotiformes: First Cytogenetic Insights into Rhabdolichops (Sternopygidae)

We report the first comparative cytogenetic analysis of two species from electrogenic fish of genus Rhabdolichops (Sternopygidae, Gymnotiformes): Rhabdolichops troscheli and Rhabdolichops cf eastwardi. R. troscheli has 2n = 54 (fundamental number [FN] = 66), whereas R. cf. eastwardi has 2n = 74 (FN = 78). C-banding revealed centromeric constitutive heterochromatin in both species. Ag-NORs mapped on pair 6 in R. troscheli and pair 30 in R. cf eastwardi. Fluorescense in situ hybridization with 18S rDNA probes confirmed the Ag-NOR staining results and revealed additional (presumably silent) ribosomal genes on pairs 12, 13, 21, 23, 26, and 27 in R. cf eastwardi. 5S rDNA was found on the centromeres of pair 7 in both species. Telomeric probes showed only distal locations. Dispersed signal patterns were obtained using probes for retrotransposons Rex1 and Rex3. Histone H1 and H3 genes were found together on pair 6 in R. cf eastwardi. The high diploid number found in Rhabdolichops suggests that chromosome fission may have contributed to its chromosomal evolution, phylogenetic relationship of the Sternopygidae suggests that this increase in diploid number could be a synapomorphic characteristic of genus Rhabdolichops. Although both species are phylogenetically close related, their karyotype structure has undergone divergent evolutionary directions. All in all, our results strongly suggest that R. cf eastwardi experencied recent intense genome reorganization.

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.

Chromosomal Mapping of Repetitive DNA Sequences in the Genus Bryconamericus (Characidae) and DNA Barcoding to Differentiate Populations

The mapping of repetitive DNA sites by fluorescence in situ hybridization has been widely used for karyotype studies in different species of fish, especially when dealing with related species or even genera presenting high chromosome variability. This study analyzed three populations of Bryconamericus, with diploid number preserved, but with different karyotype formulae. Bryconamericus ecai, from the Forquetinha river/RS, presented three new cytotypes, increasing the number of karyotype forms to seven in this population. Other two populations of Bryconamericus sp. from the Vermelho stream/PR and Cambuta river/PR exhibited interpopulation variation. The chromosome mapping of rDNA sites revealed unique markings among the three populations, showing inter- and intrapopulation variability located in the terminal region. The molecular analysis using DNA barcoding complementing the cytogenetic analysis also showed differentiation among the three populations. The U2 small nuclear DNA repetitive sequence exhibited conserved features, being located in the interstitial region of a single chromosome pair. This is the first report on its occurrence in the genus Bryconamericus. Data obtained revealed a karyotype variability already assigned to the genus, along with polymorphism of ribosomal sites, demonstrating that this group of fish can be undergoing a divergent evolutionary process, constituting a substantive model for studies of chromosomal evolution.

Variability and evolutionary implications of repetitive DNA dynamics in genome of Astyanax scabripinnis (Teleostei, Characidae)

DNA sequences of multiple copies help in understanding evolutionary mechanisms, genomic structures and karyotype differentiation. The current study investigates the organization and distribution of different repetitive DNA in the standard complement and B chromosomes in Astyanax scabripinnis (Jenyns, 1842) chromosomes from three allopatric populations in Campos do Jordão region, São Paulo State, Brazil. The location of microsatellite sequences showed different chromosome distribution between Lavrinha Farm Stream (LFS) and Lake of Pedalinho (LP) populations. However, the karyotype of these populations basically followed the pattern of dispersed distribution in the A complement, conspicuous in telomeric/interstitial regions and preferential accumulation in the B chromosome. The B chromosome showed heterogeneous location of microsatellite probes CA, CAC and GA. The H3 and H4 histone genes were isolated from the total genome of the species and then the chromosomal mapping was performed by fluorescence in situ hybridization (FISH). The FISH signals showed high similarity for the probes H3 and H4 mapping in genomes of the populations analyzed. The sequences (GATA) _n revealed a sex-specific trend between the chromosomal location in males and females at (LFS) and (LP) populations. Although species that comprise the Astyanax scabripinnis complex do not have morphologically differentiated sex chromosomes, the preferential GATA location - sex-associated - may represent a sex chromosome in differentiation.

Karyotype Diversity in Doradidae (Siluriformes, Doradoidea) and Presence of the Heteromorphic ZZ/ZW Sex Chromosome System in the Family

Karyotypes and other chromosomal markers as revealed by conventional and molecular cytogenetic protocols in four species of the catfish family Doradidae from the Araguaia-Tocantins river basin, namely Hassar wilderi, Leptodoras cataniae, Tenellus leporhinus and Tenellus trimaculatus were examined. All species had diploid chromosome number 2n = 58 and karyotypes dominated by biarmed chromosomes, simple NOR phenotype, that is, one chromosome pair bearing this site in terminal position, but some differences in karyotypes and distribution of constitutive heterochromatin, position of rDNA sites. Such characteristics appeared species-specific. A ZZ/ZW sex chromosome system was found in Tenellus trimaculatus, resulting likely from the amplification of the heterochromatin, followed by a paracentric inversion. Our results confirmed low karyotype differentiation observed until now among representatives of this endemic catfish family.

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.

Evolutionary Dynamics of rDNAs and U2 Small Nuclear DNAs in Triportheus (Characiformes, Triportheidae): High Variability and Particular Syntenic Organization

Multigene families correspond to a group of genes tandemly repeated, showing enormous diversity in both number of units and genomic organization. In fishes, unlike rDNAs that have been well explored in cytogenetic studies, U2 small nuclear RNA (snRNA) genes are poorly investigated concerning their chromosomal localization. All Triportheus species (Characiformes, Triportheidae) studied so far carry a ZZ/ZW sex chromosomes system, where the W chromosome contains a huge 18S rDNA cistron. In some species the syntenic organization of rDNAs on autosomes was also verified. To explore this particular organization, we performed three-color-fluorescence in situ hybridization using 5S, 18S rDNA, and U2 snRNA genes as probes in eight Triportheus species. This work represents the first one analyzing the chromosomal distribution of U2 snRNA genes in genomes of Triportheidae. The variability in number of rDNA clusters, and the divergent syntenies for these three multigene families, put in evidence their evolutionary dynamism, revealing a much more complex organization of these genes than previously supposed for closely related species. Our study also provides additional data on the accumulation of repetitive sequences in the sex-specific chromosome. Besides, the chromosomal organization of U2 snDNAs among fish species is also reviewed.

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

ABSTRACT 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.

Karyotype analysis of three species of Corydoras (Siluriformes: Callichthyidae) from southern Brazil: rearranged karyotypes and cytotaxonomy

ABSTRACT The genus Corydoras comprises a diversity of species with different diploid numbers. We compared cytogenetic data among Corydoras species from different rivers of the Ponta Grossa Arch region in southern Brazil. Corydoras ehrhardti and C. aff. paleatus have a similar karyotype formula and the same diploid number (2n = 44). Corydoras lacrimostigmata has a higher diploid number, with 2n = 58 chromosomes. Fluorescence in situ hybridization using 5S and 18S ribosomal DNA probes suggests that these ribosomal DNA sequences are involved in chromosomal rearrangements in these Corydoras species. 5S rDNA is a chromosomal marker that is considered to be unique to the species analyzed in this study. Signals of interstitial telomeric sites are seen in a chromosome pair of C. lacrimostigmata, suggesting chromosomal rearrangements via fusions or translocations. This study revealed that C. ehrhardti and C. aff. paleatus have exclusive chromosomal markers associated with chromosome differentiation, which we speculate to prevent genetic introgression.

Cytogenetic data on Ancistrus sp. (Siluriformes, Loricariidae) of the Paraguay River basin (MS) sheds light on intrageneric karyotype diversification

Ancistrus Kner, 1854 is a diverse catfish genus, currently comprising 66 valid species, but karyotype data were recorded for 33 species, although only ten have their taxonomic status defined. Considerable karyotype diversity has been found within this genus, with 2n varying from 34 to 54 and structural variability including heteromorphic sex chromosomes. In many cases, uncertainty on the taxonomic status of the study populations hampers reliable interpretation of the complex chromosomal evolutionary history of the group. This study aims to present the first karyotype data for a population of the Ancistrus sp. collected in Criminoso stream (tributary of the Paraguay River Basin, Mato Grosso do Sul, Brazil) in which a combination of different chromosomal markers was used and results integrated in broad discussion on karyotype evolution in the genus. The specimens presented 2n=42 with 18m+16sm+8st and a single NOR revealed by silver nitrate and fluorescence in situ hybridization (FISH) with 18S rDNA probe, located in pair No. 10. Clusters of 5S rDNA were located in the pericentromeric region of three chromosomes: pair No. 1 (metacentric) and one of the homologues of the nucleolar pair No. 10. Heterogeneity in the molecular composition of the heterochromatin was confirmed by the association of C-banding and fluorochrome CMA₃/DAPI-staining. Exploring the differential composition of constitutive heterochromatin in Ancistrus may provide an important perspective to understand genome organization and evolution within this group. Our data reinforce the chromosomal diversity present in Ancistrus genus and we discuss the potential sources these variation. The karyotype structure of Ancistrus sp. "Criminoso stream" appears to be consistent with the existence of a new candidate species.

First cytogenetic analysis of Ichthyoelephas humeralis (Günther, 1860) by conventional and molecular methods with comments on the karyotypic evolution in Prochilodontidae

We used conventional cytogenetic techniques (Giemsa, C-banding, Ag-NOR), and fluorescent in situ hybridization (FISH) with 5S and 18S rDNA probes to investigate the karyotype and cytogenetic characteristics of Ichthyoelephas humeralis (Günther, 1860) from Ecuador. The specimens studied have a karyotype with 2n=54 biarmed chromosomes (32 M + 22 SM) and C-positive heterochromatin located on the centromeric, pericentromeric, interstitial, and terminal regions of some chromosomes. The nucleolus organizer regions occurred terminally on the long arm of chromosome pair 2. FISH confirmed the presence of only one 18S rDNA cluster with nonsyntenic localization with the 5S rDNA. Cytogenetic data allow us to refute the earlier morphological hypothesis of a sister relationship between Semaprochilodus Fowler, 1941 and Ichthyoelephas Posada Arango, 1909 and support the molecular proposal that Ichthyoelephas is a sister group to the monophyletic clade containing Prochilodus Agassiz, 1829 and Semaprochilodus.

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.

New insights of karyoevolution in the Amazonian turtles Podocnemis expansa and Podocnemis unifilis (Testudines, Podocnemidae)

BACKGROUND

Cytogenetic studies were conducted in the Brazilian Amazon turtles, Podocnemis expansa Schweigger, 1912 (PEX) and Podocnemis unifilis Troschel, 1848 (PUN) to understand their karyoevolution. Their chromosomal complements were compared using banding techniques (C, G-, Ag-NOR and Chromomycin A₃) and fluorescence in situ hybridization (FISH), and efforts were made to establish evolutionary chromosomal relationships within the Podocnemidae family.

RESULTS

Our results revealed that both species have a chromosome complement of 2n = 28. For PEX and PUN, the fundamental numbers (FNs) were 54 and 52, respectively and the karyotypic formulas (KFs) were 24 m/sm + 2st + 2a and 22 m/sm + 2st + 4a, respectively. G-banding evidenced homologies between the two species and allowed identify a heteromorphic pair (chromosome pair 10) in PUN. In PEX, constitutive heterochromatin (CH) was found in the centromeric regions of pairs 1, 2, 4, 6 and 11 and on 9p. In PUN, CH was observed in the centromeric regions of all chromosomes, and in small proximal bands on 1p, 2p, 3q, 4q, 5q, 9q, 10q and 11q. Moreover, CH amplification was seen in one of the homologs of pair 10 (the heteromorphic pair). The CMA3 staining results were consistent with the CH findings. Ag-NOR staining showed that nucleolar organizing regions (NORs) were localized in the pericentromeric region of pair 1 in both species, and this result was confirmed by the 18S rDNA FISH probe. FISH with telomeric probes identified telomeric sequences in the distal regions of all chromosomes. In addition, interstitial telomeric sequences (ITSs) were present in seven chromosome pairs of PUN, perhaps reflecting the amplification of telomere-like sequences. FISH with a probe against the transposable element (TE), Rex 6, revealed that it is dispersed in euchromatic regions of the first chromosome pairs of both species. This is the first report describing the FISH-based analysis of PEX and PUN for the 18S rDNA, Rex 6 and human telomeric sequences.

CONCLUSIONS

Our results contribute to clarifying the chromosomal homologies and rearrangement mechanisms that occurred during the evolution of these species, and may help researchers uncover new markers that will improve our understanding of the taxonomy and systematic classification of Podocnemidae.

TRIAL REGISTRATION

ISRCTN ISRCTN73824458. Registered 28 September 2014. Retrospectively registered.

Comparative Cytogenetics of Hoplerythrinus unitaeniatus (Agassiz, 1829) (Characiformes, Erythrinidae) Species Complex from Different Brazilian Hydrographic Basins

Chromosomal characteristics of Hoplerythrinus unitaeniatus populations from 5 Brazilian river basins, namely Arinos (Amazonas basin), Araguaia, Paraguai, Alto Paraná, and São Francisco were analyzed by conventional Giemsa staining, C-banding, silver nitrate impregnation, and fluorescence in situ hybridization (FISH) with 18S and 5S rDNA and telomeric sequence (TTAGGG)n probes. The diploid chromosome number was 2n = 48 in representatives of the populations from Paraguai and Alto Paraná River basins and 2n = 52 for those from the Arinos and Araguaia River basins. The São Francisco population had individuals with 2n = 50 and 52 occurring in sympatry. C-banding showed heterochromatic blocks mainly located at interstitial and pericentromeric positions in most of the chromosomes. Silver nitrate impregnation demonstrated simple NORs for representatives from Arinos and Araguaia River populations and multiple NORs for specimens from Paraguai, Alto Paraná, and São Francisco River populations. FISH with 18S and 5S rDNA probes revealed many chromosomes carrying these cistrons, with up to 21 chromosomes bearing 18S rDNA sites (Alto Rio Paraná basin) and up to 12 chromosomes with 5S rDNA sites (Paraguai basin), besides the occurrence of colocalization in all populations. FISH with telomeric sequence (TTAGGG)n detected sites in the terminal portion of the chromosomes in all populations. These data reinforce the idea that H. unitaeniatus is a species complex. Evolutionary and biogeographical aspects of the group in the Neotropical region are discussed.

Chromosomal Spreading of Microsatellites and (TTAGGG)n Sequences in the Characidium zebra and C. gomesi Genomes (Characiformes: Crenuchidae)

Sex chromosome evolution involves the accumulation of repeat sequences such as multigenic families, noncoding repetitive DNA (satellite, minisatellite, and microsatellite), and mobile elements such as transposons and retrotransposons. Most species of Characidium exhibit heteromorphic ZZ/ZW sex chromosomes; the W is characterized by an intense accumulation of repetitive DNA including dispersed satellite DNA sequences and transposable elements. The aim of this study was to analyze the distribution pattern of 18 different tandem repeats, including (GATA)n and (TTAGGG)n, in the genomes of C. zebra and C. gomesi, especially in the C. gomesi W chromosome. In the C. gomesi W chromosome, weak signals were seen for (CAA)10, (CAC)10, (CAT)10, (CGG)10, (GAC)10, and (CA)15 probes. (GA)15 and (TA)15 hybridized to the autosomes but not to the W chromosome. The (GATA)n probe hybridized to the short arms of the W chromosome as well as the (CG)15 probe. The (GATA)n repeat is known to be a protein-binding motif. GATA-binding proteins are necessary for the decondensation of heterochromatic regions that hold coding genes, especially in some heteromorphic sex chromosomes that may keep genes related to oocyte development. The (TAA)10 repeat is accumulated in the entire W chromosome, and this microsatellite accumulation is probably involved in the sex chromosome differentiation process and crossover suppression in C. gomesi. These additional data on the W chromosome DNA composition help to explain the evolution of sex chromosomes in Characidium.

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.

Chromosomal characterization in two species of an Astyanax bimaculatus complex (Characidae, Characiformes) using different techniques of chromosome banding

Astyanax has been the subject of extensive cytogenetic studies due to its wide karyotypic diversity. This genus comprises species complexes, namely groups of fish of difficult morphological differentiation, such as the bimaculatus complex, which includes the characids with a rounded humeral spot. Thence, the present study proposed to accomplish a cytogenetic characterization of two species of this complex: A. asuncionensis and A. altiparanae, aiming to find chromosomal markers that differentiate these species, as well as achieve a better understanding of the karyotype evolution in the genus. For this we used different techniques of chromosome banding as C-banding, impregnation by silver nitrate, fluorochrome staining and FISH with 18S rDNA probe. This is the first cytogenetic study in A. asuncionensis, from Miranda river, which presented 2n = 50 and 18 m + 22sm + 6st + 4a (FN = 96) and single NORs. The populations of A. altiparanae also presented 2n = 50, but with different karyotypic formulae: the population of the Quexada river presented 16 m + 24sm + 4st + 6a (FN = 94) and the Esperança stream and Jacutinga river showed 16 m + 20sm + 4st + 10a (FN = 90). All analyzed populations showed an interindividual variation in the number and location of the nucleolar organizer regions (NORs). Single and multiple NORs were detected either by impregnation with silver nitrate or by FISH with 18S rDNA probe. After C-banding, the two species differed in relation to the composition and heterochromatin distribution. The meiotic cells of A. altiparanae male individuals were also analyzed, showing that, despite the high karyotype variability, chromosome pairing occurs normally. The data show that A. altiparanae and A. asuncionensis share some characteristics with other species of the bimaculatus complex, suggesting a close phylogenetic relationship among those species. However, some features can be used as differentiation chromosomal markers in altiparanae/asuncionensis morphotypes, which could result from a natural speciation process.

Comparative cytogenetic analysis of four species of Dendropsophus (Hylinae) from the Brazilian Atlantic forest

We conducted a cytogenetic study of four hyline frog species (Dendropsophus elegans, D. microps, D. minutus and D. werneri) from southern Brazil. All species had 2n = 30 chromosomes, with interspecific and intraspecific variation in the numbers of metacentric, submetacentric, subtelocentric and telocentric chromosomes. C-banding and fluorochrome staining revealed conservative GC-rich heterochromatin localized in the pericentromeric regions of all species. The location of the nucleolus organizer regions, as confirmed by fluorescent in situ hybridization, differed between species. Telomeric probes detected sites that were restricted to the terminal regions of all chromosomes and no interstitial or centromeric signals were observed. Our study corroborates the generic synapomorphy of 2n = 30 chromosomes for Dendropsophus and adds data that may become useful for future taxonomic revisions and a broader understanding of chromosomal evolution among hylids.

Paecilomyces variotii: A Fungus Capable of Removing Ammonia Nitrogen and Inhibiting Ammonia Emission from Manure

Ammonia (NH3) emissions from animal manure are a significant environmental and public concern. Despite the numerous studies regarding NH3 emissions from manure, few of them have considered microbial nitrification approaches, especially fungal nitrification. In this study, a filamentous fungus was isolated from chicken manure and was used for nitrification. The species was Paecilomyces variotii by morphological characteristics and 18S rDNA gene sequencing. It played the biggest role in the removal of ammonium at pH 4.0-7.0, C/N ratio of 10-40, temperature of 25-37°C, shaking speed of 150 rpm, and with glucose as the available carbon source. Further analysis revealed that all ammonium was removed when the initial ammonium concentration was less than 100 mg/L; 40% ammonium was removed when the initial ammonium concentration was 1100 mg/L. The results showed that the concentration of ammonia from chicken manure with strain Paecilomyces variotii was significantly lower than that in the control group. We concluded that Paecilomyces variotii has good potential for future applications in in situ ammonium removal as well as ammonia emissions control from poultry manure.

Chromosomal phylogeny of Vampyressine bats (Chiroptera, Phyllostomidae) with description of two new sex chromosome systems

BACKGROUND

The subtribe Vampyressina (sensu Baker et al. 2003) encompasses approximately 43 species and seven genera and is a recent and diversified group of New World leaf-nosed bats specialized in fruit eating. The systematics of this group continues to be debated mainly because of the lack of congruence between topologies generated by molecular and morphological data. We analyzed seven species of all genera of vampyressine bats by multidirectional chromosome painting, using whole-chromosome-painting probes from Carollia brevicauda and Phyllostomus hastatus. Phylogenetic analyses were performed using shared discrete chromosomal segments as characters and the Phylogenetic Analysis Using Parsimony (PAUP) software package, using Desmodontinae as outgroup. We also used the Tree Analysis Using New Technology (TNT) software.

RESULTS

The result showed a well-supported phylogeny congruent with molecular topologies regarding the sister taxa relationship of Vampyressa and Mesophylla genera, as well as the close relationship between the genus Chiroderma and Vampyriscus.

CONCLUSIONS

Our results supported the hypothesis that all genera of this subtribe have compound sex chromosome systems that originated from an X-autosome translocation, an ancestral condition observed in the Stenodermatinae. Additional rearrangements occurred independently in the genus Vampyressa and Mesophylla yielding the X1X1X2X2/X1X2Y sex chromosome system. This work presents additional data supporting the hypothesis based on molecular studies regarding the polyphyly of the genus Vampyressa and its sister relationship to Mesophylla.

Chromosome Mapping of 18S Ribosomal RNA Genes in Eleven Hypostomus Species (Siluriformes, Loricariidae): Diversity Analysis of the Sites

We investigated the chromosomal distribution of 18S ribosomal DNA (rDNA) in different populations of 11 species of Hypostomus collected in important Brazilian basins, namely South Atlantic, Upper Paraná, and Paraguay applying the fluorescence in situ hybridization (FISH). Hypostomus cochliodon, Hypostomus commersoni, Hypostomus hermanni, Hypostomus regani, Hypostomus albopunctatus, Hypostomus paulinus, Hypostomus aff. paulinus, Hypostomus iheringii, and Hypostomus mutucae presented multiple 18S rDNA sites while Hypostomus strigaticeps and Hypostomus nigromaculatus exhibited a single pair of chromosomes with 18S rDNA sites. The studied species presented variations in the number and position of these sites. The results accomplished were similar to those obtained by the analysis of AgNORs, revealing the same interspecific variability. Each species exhibited distinctive patterns of AgNOR and 18S rDNA distribution, which can be considered cytogenetic markers in each species of the genus and help improve the discussions on the phylogeny of the group.

ZZ/ZW sex chromosome system in the endangered fish Lignobrycon myersi Miranda-Ribeiro, 1956 (Teleostei, Characiformes, Triportheidae)

Lignobrycon myersi is an endemic fish species from a few coastal rivers in northeastern Brazil. Based on molecular evidence, Lignobrycon myersi and genera Triportheus Cope, 1872, Agoniates Müller & Troschel, 1845, Clupeacharax Pearson, 1924 and Engraulisoma Castro, 1981 were placed in the family Triportheidae. In the present work, we report the first cytogenetic data for Lignobrycon myersi to test the hypothesis that Lignobrycon and Triportheus are closely related. Studied specimens presented 2n=52 with 28 metacentric (m), 18 submetacentric (sm) and six subtelocentric (st) chromosomes for males and 27 m, 19 sm and 6 st for females, characterizing a ZZ/ZW sex chromosome system. The Z chromosome corresponds to the largest chromosome in karyotype while the W is about 50% smaller than the Z and largely heterochromatic. Terminal nucleolus organizer regions, GC-rich sites and 18S rDNA signals were detected on pair 14. However, additional 18S rDNA sites were observed in the W chromosome. The 5S rDNA was mainly detected on long arms of pair 7. The apparent synapomorphic chromosomal traits of Triportheus and Lignobrycon myersi reinforce their close phylogenetic relationship, suggesting that the ZZ/ZW chromosome system in both genera has arisen before cladogenic events.

Evolutionary trends in the family Curimatidae (Characiformes): inferences from chromosome banding

The family Curimatidae is a fish group usually considered chromosomally conserved in their diploid number. However, some studies show small changes in the karyotype microstructure, and the presence of B chromosomes, indicating a chromosomal diversification within the group, even if structural changes in the karyotypes are not visible. Few studies associate this trait with an evolutionary pattern within the family. This study aimed to characterize the karyotype, nucleolus organizer regions (NORs), and heterochromatin distribution of six species of Curimatidae of the genera Cyphocharax Fowler, 1906 and Steindachnerina Fowler, 1906: Cyphocharax voga (Hensel, 1870), Cyphocharax spilotus (Vari, 1987), Cyphocharax saladensis (Meinken, 1933), Cyphocharax modestus (Fernández-Yépez, 1948), Steindachnerina biornata (Braga et Azpelicueta, 1987) and Steindachnerina insculpta (Fernández-Yépez, 1948) and contribute data to a better understanding of the mechanisms involved in the chromosomal evolution of this group of fish. All specimens had 2n=54, m-sm, and B microchromosomes. Five species exhibited single NORs, except for Steindachnerina biornata, which showed a multiple pattern of ribosomal sites. NORs were chromomycin A3 positive (CMA3 (+)) and 4'-6-diamino-2-phenylindole (DAPI(-)) negative, exhibiting differences in the pair and chromosomal location of each individual of the species. FISH with 5S rDNA probe revealed sites in the pericentrometic position of a pair of chromosomes of five species. However, another site was detected on a metacentric chromosome of Cyphocharax spilotus. Heterochromatin distributed both in the pericentromeric and some terminal regions was revealed to be CMA3 (+)/DAPI(-). These data associated with the previously existing ones confirm that, although Curimatidae have a very conservative karyotype macrostructure, NORs and heterochromatin variability are caused by mechanisms of chromosome alterations, such as translocations and/or inversions, leading to the evolution and diversification of this group of fish.