Physical mapping of the 18S and 5S ribosomal genes in nine Characidae species (Teleostei, Characiformes)

High rDNA polymorphisms in Astyanax lacustris (Characiformes: Characidae): new insights about the cryptic diversity in A. bimaculatus species complex with emphasis on the Paraná River basin

Abstract This study aimed to identify species of Astyanax bimaculatus group from four Itaipu Reservoir tributaries (Paraná River Basin) by cytogenetics and molecular markers (COI) to investigate the possible occurrence of cryptic diversity in part of this basin. The four populations showed only one karyotype formula and simple AgNORs. FISH with 18S rDNA probe showed a high variation, and 5S rDNA probes evidenced simple sites in most of the specimens, although multiple sites are present in two specimens. The variations of 5S and 18S cistrons generated 13 cytotypes. The molecular data did not reveal cryptic diversity in the populations; however, its grouping with 82 sequences from other stretches of the Paraná River Basin originated three haplogroups (distances of 3.12% and 8.82%) and 33 haplotypes were identified. DNA Barcode suggests that cytogenetic variations represent a high polymorphism degree, and it identified the analyzed specimens as Astyanax lacustris, which confirms the morphological identification. Our data suggest that the cryptic diversity of this group in the tributaries of the Paraná River Basin is different than the proposed by the synonymizations of A. altiparanae and A. asuncionensis to A. lacustris. This study reinforces the importance of integrative cytogenetics and molecular methods for taxonomy.

Trends in Karyotype Evolution in Astyanax (Teleostei, Characiformes, Characidae): Insights From Molecular Data

The study of patterns and evolutionary processes in neotropical fish is not always an easy task due the wide distribution of major fish groups in large and extensive river basins. Thus, it is not always possible to detect or correlate possible effects of chromosome rearrangements in the evolution of biodiversity. In the Astyanax genus, chromosome data obtained since the 1970s have shown evidence of cryptic species, karyotypic plasticity, supernumerary chromosomes, triploidies, and minor chromosomal rearrangements. In the present work, we map and discuss the main chromosomal events compatible with the molecular evolution of the genus Astyanax (Characiformes, Characidae) using mitochondrial DNA sequence data, in the search for major chromosome evolutionary trends within this taxon.

Comparative cytogenetics of Astyanax (Teleostei: Characidae) from the upper Paraguay basin

ABSTRACT Astyanax is one of the most abundant and diverse taxa of fishes in the Neotropical region. In order to increase the amount of cytogenetic information for Astyanax as well as to exhibit data to subsidize future taxonomic studies, this work analyzed three species of Astyanax: two species are cryptic, and are here reported to live in syntopy (A. abramis and A. lacustris); the first karyotype description for A. pirapuan is also presented. Cytogenetic analyzes reveal a diploid number of 2n=50 chromosomes for three species, yet with differences in their karyotype morphology. The physical mapping of 18S rDNA showed up to thirteen sites in A. pirapuan and two in A. abramis and A. lacustris. The physical mapping of 5S rDNA has proven to be an effective marker for the characterization of species of Astyanax studied in this work.

Conserved number of U2 snDNA sites in Piabina argentea, Piabarchus stramineus and two Bryconamericus species (Characidae, Stevardiinae)

ABSTRACT The chromosomal location of 5S rRNA and U2 snRNA genes of Piabina argentea, Piabarchus stramineus and two Bryconamericus species from two different Brazilian river basins were investigated, in order to contribute to the understanding of evolutionary characteristics of these repetitive DNAs in the subfamily Stevardiinae. The diploid chromosome number was 2n = 52 for Bryconamericus cf. iheringii, Bryconamericus turiuba, Piabarchus stramineus and Piabina argentea. The 5S rDNA clusters were located on one chromosome pair in P. stramineus and B. cf. iheringii, and on two pairs in B. turiuba and P. argentea. The U2 snDNA clusters were located on the one pair in all species. Two-color FISH experiments showed that the co-localization between 5S rDNA and U2 snDNA in P. stramineus can represent a marker for this species. Thus, the present study demonstrated that the number of U2 snDNA clusters observed for the four species was conserved, but particular characteristics can be found in the genome of each species.

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.

Allopatric chromosomal variation in Nematocharax venustus Weitzman, Menezes & Britski, 1986 (Actinopterygii: Characiformes) based on mapping of repetitive sequences

ABSTRACT Characiformes is the most cytogenetically studied group of freshwater Actinopterygii, but karyotypical data of several taxa remain unknown. This is the case of Nematocharax , regarded as a monotypic genus and characterized by marked sexual dimorphism. Therefore, we provide the first cytogenetic report of allopatric populations of Nematocharax venustus based on distinct methods of chromosomal banding and fluorescence in situ hybridization (FISH) with repetitive DNA probes (18S and 5S rDNA). The karyotype macrostructure was conserved in all specimens and populations, independently on sex, since they shared a diploid number (2n) of 50 chromosomes divided into 8m+26sm+14st+2a. The heterochromatin was mainly distributed at pericentromeric regions and base-specific fluorochrome staining revealed a single pair bearing GC-rich sites, coincident with nucleolar organizer regions (NORs). On the other hand, interpopulation variation in both number and position of repetitive sequences was observed, particularly in relation to 5S rDNA. Apparently, the short life cycles and restricted dispersal of small characins, such as N. venustus , might have favored the divergence of repetitive DNA among populations, indicating that this species might encompass populations with distinct evolutionary histories, which has important implications for conservation measures.

Cytogenetic and Molecular Data Suggest Deuterodon pedri Eigenmann, 1907 (Teleostei: Characidae) Is a Member of an Ancient Coastal Group

The genus Deuterodon has been taxonomically recently redefined. Seven of its species have been included in this genus, whereas three others are regarded as Incertae Sedis in Characidae. One of latter is Deuterodon pedri, an endemic species from Santo Antônio River in Minas Gerais. Cytogenetic and molecular data on 21 specimens of D. pedri allowed to reevaluate the phylogenetic position of this taxon. The specimens showed karyotypic formula 12m+12sm+20st+6a, low heterochromatin content, nucleolar organizer regions present in two chromosome pairs, and 10 and 2 labeled regions by fluorescence in situ hybridization with 18S and 5S probes respectively, a karyotype similar to Deuterodon stigmaturus. The phylogenetic tree generated by a cytochrome oxidase subunit I fragment revealed that D. pedri and Deuterodon singularis are closely related and are the sister-group of Deuterodon parahybae, Deuterodon iguape, Astyanax giton, Astyanax intermedius, Astyanax ribeirae, Astyanax scabripinnis, and Probolodus heterostomus. The same arrangement was partially recovered with the nuclear gene RAG2. Our data indicate the genus Deuterodon is not monophyletic and that it is closely related to other species that occur in Brazil coastal basins.

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.

Chromosomal microstructure diversity in three Astyanax (Characiformes, Characidae) species: comparative analysis of the chromosomal locations of the 18S and 5S rDNAs

The species of genus Astyanax is widely distributed in freshwater neotropical zones. Astyanax is considered to be taxonomically confused, similar to other genera placed incertae sedis in Characidae. The cytogenetics of this genus is well characterized; species vary widely in diploid number, from 2n=36 chromosomes in Astyanax schubarti to 2n=50 for most species studied. The size, number, and position of different cytological markers vary among species and populations of Astyanax. We analyzed the karyotypes of individuals from three Astyanax species (Astyanax abramis, Astyanax altiparanae, and Astyanax eigenmanniorum) from populations not previously analyzed. We describe variations in several cytogenetic markers and the karyotypic relationships between them, specifically focusing on the characteristics of the conserved and divergent locations of the ribosomal genes. Our data are useful for establishing relationships between species and for investigating the karyotype evolution within the genus.

Twenty years of physical mapping of major ribosomal RNA genes across the teleosts: A review of research

Molecular cytogenetic data on the number and position of 45S ribosomal RNA genes (rDNA; located in nucleolus organizing regions, NORs) detected by FISH in 330 species of 77 families and 22 orders of bony fishes (Teleostei) and, additionally, 11 species of basal ray-finned fishes are compiled and analyzed. The portion of species with single rDNA sites in the sample amounts to 72%. The percentage of species with multiple NORs decreases with increasing numbers of rDNA loci per genome, i.e. scarcely 3% of species carry 4 or more rDNA-bearing chromosome pairs. 43% of all rDNA sites analyzed occur terminally on the short arms of chromosomes or constitute them. In general, terminal rDNA sites account for 87% of all examined cases. Interspecific variation in the location of single rDNA sites among related taxa, polymorphisms of multiple NORs in some groups of teleosts and analytical outcomes on the subject are reviewed.

Comparative cytogenetics in Astyanax (Characiformes: Characidae) with focus on the cytotaxonomy of the group

Astyanax is a diverse group of Neotropical fishes, whose different forms occupy different environments. This great diversity is also reflected on cytogenetic aspects and molecular markers, which have repeatedly been demonstrated by cytogenetic studies. In order to characterize the karyotype of species of this genus, six species were studied: Astyanax altiparanae, A.argyrimarginatus, A. elachylepis, A. xavante, and two new species provisionally called Astyanax sp. and A. aff. bimaculatus. A detailed cytogenetic study based on conventional staining with Giemsa, AgNORs, C-banding, base-specific fluorochromes, and FISH using ribosomal genes 18S and 5S was conducted, aiming to understand some of the chromosomal mechanisms associated with the high diversification that characterizes this group and culminated with the establishment of these species. The results showed 2n = 50 chromosomes for five species and a karyotype with 52 chromosomes in Astyanax sp. Small variations in the macrostructure of the karyotypes were identified, which were quite relevant when analyzed by classical banding, fluorochromes, and FISH methods. These differences among Astyanax spp. (2n = 50) are largely due to changes in the amount and types of heterochromatic blocks. Astyanax sp (2n = 52), in addition to variations due to heterochromatic blocks, has its origin possibly by events of centric fission in a pair of chromosomes followed by minor rearrangements.These results show an interesting karyotypic diversity in Astyanax and indicate the need of a review of the group referred as A. aff. bimaculatus and the description of Astyanax sp., including the possibility of inclusion of this unit in another genus.

Comparative cytogenetics among populations of Hollandichthys multifasciatus (Teleostei: Characidae)

Two populations of Hollandichthys multifasciatus from headwaters of adjacent river coastal basins in Paraná state, southern Brazil, were cytogenetically studied in order to evaluate intraspecific divergences. Both populations presented 2n = 50 chromosomes, divided into 14m + 18sm + 18st in the sample from Antonina and 14m + 20sm + 16st for the population from Guaraqueçaba. Analyses of active nucleolar organizer regions (Ag-NORs) and fluorescent in situ hybridization (FISH) with 18S rDNA probes revealed a single metacentric pair bearing marks at proximal positions on the short arms. The location of the 5S rDNA and GC-rich sites showed chromosomal divergence between both populations. Therefore, several population markers were detected, reflecting a population differentiation, possibly driven by the formation of Paranaguá Bay and Serra do Mar mountain range. Since the existence of a species complex in H. multifasciatus has been previously characterized by morphological, molecular, and karyotype population differentiation, this species needs to be taxonomically studied in detail.

Cytogenetic and molecular markers reveal the complexity of the genus Piabina Reinhardt, 1867 (Characiformes: Characidae)

Cytogenetic and molecular analyses were carried out in fish representative of the genus Piabina. This study specifically involved the species P. argentea and P. anhembi collected from areas of the Paranapanema and Tietê River basins, Brazil. Our findings suggest that fish classified as Piabina argentea in the Paranapanema and Tietê Rivers may represent more than one species. The samples analyzed differed by cytogenetic particularities and molecular analyses using partial sequences of the genes COI and CytB as genetic markers revealed three distinct groups of P. argentea with genetic distances sufficient to support the conclusion that the three samples analyzed are three distinct taxonomic units.

HF, Dias AL. Cytogenetic comparison between two allopatric populations of Astyanax altiparanae Garutti et Britski, 2000 (Teleostei, Characidae), with emphasis on the localization of 18S and 5S rDNA

Two populations of Astyanax altiparanae (Garutti & Britski, 2000) of the Água dos Patos stream/SP and lake Igapó/PR were analyzed. All individuals showed 2n = 50, however, different karyotypic formulae were observed. The population of the Água dos Patos stream showed 8m +24sm+6st+12a (NF=88) and the population of lake Igapó, 8m+28sm+4st+10a (NF=90). Nucleolus organizing regions (AgNORs) were observed in the terminal position on the short and long arm of different chromosomes of both populations, showing a variation from 3 to 4 chromosomes. Fluorescent in situ hybridization (FISH) using 18S rDNA probes revealed only one pair of chromosomes with fluorescent signals in the terminal site on the short arm in the Igapó lake population, while the population of Água dos Patos stream showed 4 fluorescence terminal signals, characterizing a system of simple and multiple NORs, respectively. 5S rDNA fluorescent signals were detected in the interstitial position of a pair of chromosomes in the two studied populations. Some AgNOR sites revealed to be GC-rich when stained with Chromomycin A3 (CMA3), however, AT positive regions were not observed. The data obtained show that, despite the conservation of the diploid number and location of 5S DNAr, differences in both the distribution of 18S rDNA and karyotypic formula among the populations were found, thus corroborating the existing data on chromosome variability in Astyanax altiparanae that can be significant for cytotaxonomy in this group.

Cytogenetic data on Astyanax jacuhiensis (Characidae) in the lago Guaíba and tributaries, Brazil

Cytogenetic analyses were performed in Astyanax jacuhiensis from lago Guaíba, Brazil. The diploid number was 50, with a karyotype composed of 8m+30sm+4st+8a chromosomes, FN = 92. The AgNORs were observed in 2 to 5 chromosomes, with intra- and interindividual variation. The sm pair 8 observed always carried NORs on the short arms, presenting size heteromorphism between homologous. Fluorescence in situ hybridization (FISH) with an 18S rDNA probe only confirmed the location of ribosomal cistrons in the sm pair 8, and heteromorphism of these regions between the homologous chromosomes. C-banding revealed the occurrence of weak C-positive heterochromatin in the pericentromeric regions of several chromosomes, in addition to more evident bands interstitially located on some chromosome pairs and in the terminal region of the short arms in pair 8. C-banding plus CMA3 revealed light fluorescent signals in different chromosomes of the karyotype, with a strong terminal site in pair 8, indicating the occurrence of several GC-rich heterochromatic regions in this species. Our results provide the first description of the Astyanax jacuhiensis karyotype, showing karyotype similarities when compared to various populations of A. altiparanae and A. bimaculatus, indicating that chromosomal features are very similar for these three species.

Comparative cytogenetics among populations of Astyanax altiparanae (Characiformes, Characidae, Incertae sedis)

Cytogenetic data are presented for Astyanax altiparanae populations from three Brazilian hydrographic systems. The chromosomal data obtained in A. altiparanae support the hypothesis of diploid number conservation. However, small differences in the karyotype formula and number of nucleolar organizer regions were observed in these populations. The apparent karyotypical similarity among the studied populations strongly suggests a close relationship among them with some chromosomal divergences due to gene flow restriction.