On the diploid state of the fish order Ostariophysi

Chromosomal characterization of three species of Serrasalmini (Serrasalmidae: Characiformes)

The tribe Serrasalmini is a diverse group with paraphyletic genera and taxonomic uncertainties. Several studies have been carried out in this group of fish in order to understand this problem, including the cytogenetic approach. In this study, three species of a clade of Serrasalmini were characterized cytogenetically - Pristobrycon striolatus, Catoprion absconditus and Pygopristis denticulatus. The three species presented diploid number (2n) equal to 62 chromosomes, of one and two arms, with karyotypic formulas and species-specific fundamental numbers. Heterochromatin is centromeric and terminal (bi-telomeric) in most chromosomes, with a conspicuous interstitial block at pair 1 (m) in all three species. The nucleolar organizer regions were multiple and C-band positive, and their location was confirmed via 18S ribosomal DNA mapping; however, with additional sites. The 5S rDNA was located in interstitial region of long arm of pair 1 (m), in the three species (homeologous). Moreover, we observed synteny between 18S and 5S in the species C. absconditus and P. denticulatus, which, according to fiber-FISH, are interspersed. Thus, the maintenance of 2n (62) evidences the diversification of chromosomal formulas within the clade by non-Robertsonian rearrangements and reflects the paraphyly of the related species.

Molecular inferences about the genus Hypostomus Lacépède, 1803 (Siluriformes: Loricariidae): a review

This review compiles and discusses the use of genetic markers applied in the study of the fish genus Hypostomus Lacépède, 1803 (Siluriformes: Loricariidae). The database comprises 51 peer-review articles that were published in the last 52 years (1968-2020) and that approach analysis based on different classes of genetic markers. The use of cytogenetic and enzymatic markers was predominantly especially in population studies with the genus Hypostomus, while mitochondrial markers were the majority in phylogenetic studies. Although significant methodological advances have occurred for molecular evaluation, they are still modestly applied to the study of neotropical fish genera, in which Hypostomus is included. New perspectives, especially on integrative approaches, are needed to improve our knowledge of the genetic functionality of fishes.

First Record on Sex Chromosomes in a Species of the Family Cynodontidae: Cynodon gibbus (Agassiz, 1829)

The fish family Cynodontidae belongs to the superfamily Curimatoidea, together with the Hemiodontidae, Serrasalmidae, Parodontidae, Prochilodontidae, Chilodontidae, Curimatidae, and Anostomidae. The majority of the species of this superfamily that have been analyzed to date have a diploid chromosome number of 2n = 54. Differentiated sex chromosomes (with female heterogamety) have been observed only in the Prochilodontidae, Parodontidae, and Anostomidae. The present study provides the first description of differentiated sex chromosomes in the cynodontid species Cynodon gibbus, which has a ZZ/ZW system, and shows that repetitive DNA has played a fundamental role in the differentiation of these sex chromosomes.

Cytogenetic Characterization of Two Metynnis Species (Characiformes, Serrasalmidae) Reveals B Chromosomes Restricted to the Females

Karyotypes and chromosomal characteristics with focus on B chromosomes of 2 species of the serrasalmid genus Metynnis, namely M. lippincottianus and M. maculatus, were examined using conventional (C-banding) and molecular (FISH mapping of minor and major rDNAs and Rex1, Rex3, and Rex6 retrotransposable elements) protocols. Both species possessed a diploid chromosome number of 2n = 62 and karyotypes composed of 32 metacentric + 28 submetacentric + 2 subtelocentric and 32 metacentric + 26 submetacentric + 4 subtelocentric, respectively; one small B element was found in the female genome of M. lippincottianus. C-banding revealed heterochromatin in the pericentromeric and terminal portions of all chromosomes of both species; the B chromosome was entirely heterochromatic. FISH showed 18S rDNA sites in 2 chromosome pairs in both species (pairs 19 and 22), and a large block in the B chromosome, while 5S rDNA signals were detected in the first pair of subtelocentric chromosomes in both species, moreover in M. maculatus an additional labeled pair 4 was observed. Mapping of the Rex1, Rex3, and Rex6 retrotransposable elements in the genomes of M. lippincottianus and M. maculatus indicated that they were dispersed throughout nearly all the chromosomes of the complement, except for the B chromosome of M. lippincottianus.

Chromosomal distribution of the retroelements Rex 1, Rex 3 and Rex 6 in species of the genus Harttia and Hypostomus (Siluriformes: Loricariidae)

ABSTRACT The transposable elements (TE) have been widely applied as physical chromosome markers. However, in Loricariidae there are few physical mapping analyses of these elements. Considering the importance of transposable elements for chromosomal evolution and genome organization, this study conducted the physical chromosome mapping of retroelements (RTEs) Rex1, Rex3 and Rex6 in seven species of the genus Harttia and four species of the genus Hypostomus, aiming to better understand the organization and dynamics of genomes of Loricariidae species. The results showed an intense accumulation of RTEs Rex1, Rex3 and Rex6 and dispersed distribution in heterochromatic and euchromatic regions in the genomes of the species studied here. The presence of retroelements in some chromosomal regions suggests their participation in various chromosomal rearrangements. In addition, the intense accumulation of three retroelements in all species of Harttia and Hypostomus, especially in euchromatic regions, can indicate the participation of these elements in the diversification and evolution of these species through the molecular domestication by genomes of hosts, with these sequences being a co-option for new functions.

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

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

Physical mapping of the 5S and 18S rDNA in ten species of Hypostomus Lacépède 1803 (Siluriformes: Loricariidae): evolutionary tendencies in the genus

Hypostomus is a diverse group with unclear aspects regarding its biology, including the mechanisms that led to chromosome diversification within the group. Fluorescence in situ hybridization (FISH) with 5S and 18S rDNA probes was performed on ten Hypostomini species. Hypostomus faveolus, H. cochliodon, H. albopunctatus, H. aff. paulinus, and H. topavae had only one chromosome pair with 18S rDNA sites, while H. ancistroides, H. commersoni, H. hermanni, H. regani, and H. strigaticeps had multiple 18S rDNA sites. Regarding the 5S rDNA genes, H. ancistroides, H. regani, H. albopunctatus, H. aff. paulinus, and H. topavae had 5S rDNA sites on only one chromosome pair and H. faveolus, H. cochliodon, H. commersoni, H. hermanni, and H. strigaticeps had multiple 5S rDNA sites. Most species had 18S rDNA sites in the telomeric region of the chromosomes. All species but H. cochliodon had 5S rDNA in the centromeric/pericentromeric region of one metacentric pair. Obtained results are discussed based on existent phylogenies for the genus, with comments on possible dispersion mechanisms to justify the variability of the rDNA sites in Hypostomus.

Chromosome mapping of repetitive sequences in four Serrasalmidae species (Characiformes)

The Serrasalmidae family is composed of a number of commercially interesting species, mainly in the Amazon region where most of these fishes occur. In the present study, we investigated the genomic organization of the 18S and 5S rDNA and telomeric sequences in mitotic chromosomes of four species from the basal clade of the Serrasalmidae family: Colossoma macropomum, Mylossoma aureum, M. duriventre, and Piaractus mesopotamicus, in order to understand the chromosomal evolution in the family. All the species studied had diploid numbers 2n = 54 and exclusively biarmed chromosomes, but variations of the karyotypic formulas were observed. C-banding resulted in similar patterns among the analyzed species, with heterochromatic blocks mainly present in centromeric regions. The 18S rDNA mapping of C. macropomum and P. mesopotamicus revealed multiple sites of this gene; 5S rDNA sites were detected in two chromosome pairs in all species, although not all of them were homeologs. Hybridization with a telomeric probe revealed signals in the terminal portions of chromosomes in all the species and an interstitial signal was observed in one pair of C. macropomum.

Population divergence and peculiar karyoevolutionary trends in the loricariid fish Hypostomus aff. unae from northeastern Brazil

Loricariidae (Siluriformes, Hypostominae) is one of the most diverse catfish families. In spite of the wide distribution of loricariids in South America, cytogenetic reports are available for only a few species, mostly from southern and southeastern Brazil. We made the first chromosomal analysis of Hypostomus aff. unae from the Contas River basin in northeastern Brazil. Four populations isolated by short distances but from distinct landscapes were studied based on conventional staining, C-banding, argyrophilic nucleolar organizer regions (Ag-NOR), CMA(3)/DAPI fluorochrome staining, and fluorescent in situ hybridization with 18S rDNA probes. Although sharing the same diploid number (2n = 76) and NOR locations, each population presented exclusive karyotype formulae and specific patterns of heterochromatic and AT-rich regions. The derived karyotypes of H. aff. unae (2n >54; high number of acrocentrics bearing AT-rich interstitial heterochromatin) indicated a divergent karyoevolution, mostly driven by centric fissions, pericentric inversions and particular heterochromatin dispersion models. This finding of distinct evolutionary units in H. aff. unae will be useful for understanding the natural history of loricariids from relatively unexplored coastal basins in South America.

First karyotype description of Hypostomus iheringii (Regan, 1908): a case of heterochromatic polymorphism

In this study, which is the first karyotype analysis of Hypostomus iheringii, nine specimens collected in Córrego da Lapa (tributary of the Passa-Cinco River) showed a diploid number of 80 chromosomes. Silver nitrate staining and fluorescence in situ hybridization (FISH) with an 18S rDNA probe revealed the presence of multiple nucleolus organizer regions (NORs) (chromosome pairs 13, 20, and 34). FISH with a 5S rDNA probe showed that this cistron was only present in chromosome pair 2. When the karyotypes of individual animals were compared, unique heterochromatic polymorphisms were detected on chromosome pairs 1 and 5. Specifically, specimens had heterochromatic blocks (h+h+) on both chromosomes, one chromosome with heterochromatic blocks (h+h-) or chromosomes that lacked heterochromatic blocks (h-h-). Considering that heteromorphic pattern is not correlated with variation in size, the process of heterochromatinization might act on the long arms of these chromosomes. In summary, all chromosomal markers indicate that the karyotype of Hypostomus iheringii is highly differentiated and that the heterochromatinization of chromosomal segments may have contributed to its karyotypic differentiation.

Cytogenetic characterization of four species of the genus Hypostomus Lacépède, 1803 (Siluriformes, Loricariidae) with comments on its chromosomal diversity

Cytogenetic analyses were performed on fishes of the genus Hypostomus (Hypostomus ancistroides (Ihering, 1911), Hypostomus strigaticeps (Regan, 1908), Hypostomus regani (Ihering, 1905), and Hypostomus paulinus (Ihering, 1905)) from the seven tributaries of the Paranapanema River Basin (Brazil) by means of different staining techniques (C-, Ag-, CMA3- and DAPI-banding) and fluorescence in situ hybridization (FISH) to detect 18S rDNA sites. All species showed different diploid numbers: 2n=68 (10m+26sm+32st-a) in Hypostomus ancistroides, 2n=72 (10m+16sm+46st-a) in Hypostomus strigaticeps, 2n=72 (10m+18sm+44st-a) in Hypostomus regani and 2n=76 (6m+16sm+54st-a) in Hypostomus paulinus. Ag-staining and FISH revealed various numbers and locations of NORs in the group. NORs were usually located terminally on the subtelocentric/acrocentric chromosomes: on the long arm in Hypostomus strigaticeps (2 to 4) and Hypostomus paulinus (2); and on the short arm in Hypostomus ancistroides (2 to 8) and Hypostomus regani (2 to 4). Conspicuous differences in heterochromatin distribution and composition were found among the species, terminally located in some st-a chromosomes in Hypostomus ancistroides, Hypostomus strigaticeps, and Hypostomus paulinus, and interstitially dispersed in most st-a chromosomes, in Hypostomus regani. The fluorochrome staining indicated that different classes of GC and/or AT-rich repetitive DNA evolved in this group. Our results indicate that chromosomal rearrangements and heterochromatin base-pair composition were significant events during the course of differentiation of this group. These features emerge as an excellent cytotaxonomic marker, providing a better understanding of the evolutionary mechanisms underlying the chromosomal diversity in Hypostomus species.

Description of karyotype in Hypostomus regani (Ihering, 1905) (Teleostei, oricariidae) from the Piumhi river in Brazil with comments on karyotype variation found in Hypostomus

The paper represents a comparative cytogenetic analysis of three populations of Hypostomus regani in Brazil.Two populations belong to the Upper Paraná River Basin and the third one, the karyotype of which is described for the first time, was probably introduced into the São Francisco River Basin through transposition from the Piumhi River. Karyotype features of populations of Hypostomus regani from the Piracicaba and Tietê River Basins are also discussed. The occurrence of Hypostomus regani in the São Francisco River Basin is reported for the first time here. The study also revealed distinct differences in the location of the Ag-NORs between the analyzed populations that enable individuals from the Piumhi River, Mogi-Guaçu River and Tietê River to be distinguished from one another. Thus, the data obtained indicate the possibility of geographic variation fixing different karyotypes even in the same basin of origin.

Mechanisms of chromosomal evolution and its possible relation to natural history characteristics in Ancistrus catfishes (Siluriformes: Loricariidae)

Ancistrus is the most speciose genus of the tribe Ancistrini, with 58 valid species and many yet to be described. Cytogenetic studies were conducted on five apparently undescribed species from the Amazon basin, which showed different diploid numbers: Ancistrus sp. Purus (2n = 34); Ancistrus sp. Macoari (2n = 46); Ancistrus sp. Dimona (2n = 52); Ancistrus sp. Vermelho (2n = 42) and Ancistrus sp. Trombetas (2n = 38). All species possessed only one pair of NOR-carrying chromosomes, but with extensive variation in both the location on the chromosome as well as in the position of the ribosomal sites on the karyotype. The karyotypic evolution of Ancistrus species seems to be based on chromosomal rearrangements, with a tendency to a reduction of the diploid number. Two new instances of XX/XY sex chromosomes for Ancistrus species, based on the heteromorphism in the male karyotype, were also recorded. The large karyotypic diversity among Ancistrus species may be related to biological and behavioural characteristics of these fish that include microhabitat preferences, territoriality and specialized reproductive tactics. These characteristics may lead to a fast rate of fixation of chromosomal mutations and eventually speciation across the basin.

Karyotypic relationships among the tribes of Hypostominae (Siluriformes: Loricariidae) with description of XO sex chromosome system in a Neotropical fish species

The family Loricariidae, with about 683 species, is one the largest fish families in the world. The subfamily Hypostominae was recently reviewed and is now divided in five tribes. With the main objective of contributing to a better understanding of the relationships of the members of the subfamily Hypostominae, cytogenetic analyses were conducted in seven species (three Hypostomini, three Pterygoplichthini and two Ancistrini) from Brazil and Venezuela. In Pterygoplichthini, all species show 2n = 52 chromosomes. In Hypostomini Hypostomus ancistroides has 2n = 68, H. regani 2n = 72 and Hypostomus goyazensis 2n = 72 chromosomes. In Ancistrini Ancistrus n. sp. 1 has 2n = 39/40 with a sex chromosome system of the type XX/X0, which is a novelty for neotropical fishes, and Ancistrus n. sp. 2 has 2n = 52 chromosomes. Six species have single Ag-NORs and two multiple Ag-NORs. The possible cytogenetic relationships among the species of Hypostominae are discussed.

Comparative cytogenetic analysis of eleven species of subfamilies Neoplecostominae and Hypostominae (Siluriformes: Loricariidae)

The family Loricariidae with about 690 species divided into six subfamilies, is one of the world's largest fish families. Recent studies have shown the existence of several problems in the definition of natural groups in the family, which has made the characterization of the subfamilies and even of some genera quite difficult. With the main objective of contributing for a better understanding of the relationships between loricariids, cytogenetic analysis were conducted with two species of Neoplecostominae and nine species of Hypostominae that, according to morphological and molecular data, may belong to a new monophyletic unit. The results obtained showed a marked chromosomal conservation with the presence of 2n = 54 chromosomes and single interstitial Ag-NORs in all species analyzed. Considering that Neoplecostominae is the primitive sister-group of all other loricariids, with exception of Lithogeneinae, this karyotypic structure may represent the primitive condition for the family Loricariidae. The cytogenetic characteristics partaken by the species of Neoplecostominae and Hypostominae analyzed in the present study reinforce the hypothesis that the species of both these subfamilies might belong to a natural group.

Karyotypic diversity and evolution of Loricariidae (Pisces, Siluriformes)

We present cytogenetic analyses of four fish species, belonging to four Loricariidae subfamilies: Neoplecostomus microps (Neoplecostominae) with 2n=54 chromosomes, Harttia loricariformis (Loricariinae) with 2n=56 chromosomes, Hypostomus affinis (Hypostominae) with 2n=66 chromosomes and Upsilodus sp. (Upsilodinae), with 2n=96 chromosomes. In addition to karyotypes, data on the location of 18s rDNA sites are presented, derived from indirect (silver nitrate impregnation) and direct (FISH) methods. There is only one pair of nucleolar organizing regions (NORs) per species, except in H. affinis. Diversity and NOR macrokaryotypic evolution in the species analyzed are discussed in relation to the evolution of the Loricariidae as a whole. In addition, a revision of the cytogenetic data available for this family is presented.

Application of comparative genomics in fish endocrinology

This review discusses the ways in which comparative genomics can contribute to the study of fish endocrinology. First, the phylogenetic position of fish and an overview of their specific endocrine systems are presented. The emphasis will be on teleosts because they are the most abundant fishes and because most data are available for this group. Second, the complexity of fish genomics is reviewed. With the vast array of genome sizes and ploidy levels, assignment of gene orthology is more difficult in fish, but this is an absolute prerequisite in functional analysis and it is important to be aware of such genome plasticity when cloning genes. The ease with which a gene is cloned at the genomic level is directly related to genome size and complexity, a factor that is not known in the majority of fish species. Finally, the methodology is presented along with specific examples of parathyroid hormone-related protein (PTHrP) (a previously unidentified hormone in fish), calcium-sensing receptor, and calcitonin (with a duplication of this particular ligand in Fugu rubripes). Preliminary data also suggest that there are further duplicated genes in the calcium regulatory system. Comparative genomics has provided a valuable approach for isolating and characterizing a range of fish genes involved in calcium regulation. However, for understanding the physiology and endocrine regulation of this system, particularly with regard to gene duplication, an alternative approach is required in which conventional endocrinology techniques will play a significant role.

Trends in the karyotype evolution of Loricariidae fish (Siluriformes)

Six species of Loricariidae belonging to the subfamilies Hypostominae (Hypostomus emarginatus, Rhinelepsis aspera, Pogonopoma wertheimeri), Ancistrinae (Panaque cf. nigrolineatus, Hemiancistrus sp.) and Loricariinae (Sturisoma cf. nigrirostrum) were studied cytogenetically. The results show that 2n = 54 represents the basal diploid number for this fish family. Different trends in the karyotypic evolution can be seen among the subfamilies: Hypostominae and Loricariinae species present diversified karyotypic macrostructures, while the Ancistrinae appear to show more conserved karyotypes. Among the Hypostominae, the genus Hypostomus had a wide karyotypic variation (2n = 52 to 80), where centric fissions seem to play an important role in this chromosomal divergence. The nucleolar organizing regions were diversified, and occurrence of multiple NORs was frequent. Heteromorphic chromosomes belonging to distinct sex chromosome systems can also occur infrequently among the Loricariidae.

Characterization of three corticotropin-releasing factor receptors in catfish: a novel third receptor is predominantly expressed in pituitary and urophysis

The present study reports the isolation of three complementary DNA (cDNA) clones encoding distinct subtypes of CRF receptors from the diploid catfish (cf) species, Ameiurus nebulosus. The first clone encodes a 446-amino acid protein (cfCRF-R1) that is highly homologous to mouse (m) CRF-R1 (93% identical). The cfCRF-R1 messenger RNA is highly expressed in the brain, and its distribution pattern correlates well with that of mammalian CRF-R1, except for weak expression in the pituitary. When transiently expressed in COS-7 cells, cfCRF-R1 bound CRF, urotensin I, and sauvagine with similar affinities. The second full-length cDNA, which was cloned from catfish heart, encodes a 406-amino acid protein that showed homology to murine CRF-R2 (88%) and when expressed in COS-7 cells preferentially bound sauvagine. The highest level of cfCRF-R2 expression was observed in the heart. The third full-length cDNA clone, which encodes a 428-amino acid protein, is structurally closer to cfCRF-R1 (85%) than to cfCRF-R2 (80%). This novel CRF receptor (cfCRF-R3) bound CRF with a 5-fold higher affinity than urotensin I and sauvagine and was expressed in the pituitary gland, urophysis, and brain. The presence of three different CRF receptors, each with distinct tissue distribution and ligand binding properties, suggests a complex CRF/urotensin I system.

Heterochromatin patterns and karyotype relationships within and between the genera Brycon and Salminus (Pisces, Characidae)

Chromosomes of two Brycon species (B. lundii and B. microlepis) and Salminus hilarii were analyzed. Based on constitutive heterochromatin distribution patterns, karyotypic relationships within and between Bryconinae and Salmininae were examined. A monophyletic origin for the genus Brycon, comprising at least two chromosome synapomorphies (presence of two large submetacentric bearing paracentromeric and telomeric heterochromatin), is suggested. Moreover, Bryconinae and Salmininae may represent a monophyletic unit among Characidae, as they share several chromosome features.

Fish cell lines: establishment of a line from ovaries of channel catfish

A cell line was established from the ovaries of a healthy, juvenile channel catfish, Ictalurus punctatus. These cells, designated CCO, have been passed 130 times during 3 years. The cells grow well in Eagle's MEM-10 at a temperature of 30 degrees C. Species of origin of the cells was confirmed by a cytotoxic dye exclusion test. The cells were found to be free of bacterial and fungal contamination. A study of chromosome preparations indicated that the karyotype is still in a state of flux. The CCO line replicated channel catfish virus but was refractory to 12 other viruses, 4 from fish, 1 from birds, and 7 from mammals.

DNA reassociation kinetics in diploid and phylogenetically tetraploid cyprinidae

Four diploid and three phylogenetically tetraploid Cyprinidae (Ostariophysi) have been characterized as for nuclear DNA content, modal chromosome number and DNA reassociation kinetics (hydroxyapatite chromatography). Among the diploid species nuclear DNA content (10(-12) g DNA/2C) was 1.62 for Tinca tinca, 1.87 for Scardinius erythrophthalmus, 2.53 for Leuciscus cephalus and 2.75 for Alburnus alburnus, while the phylogenetically tetraploid species Carassius auratus, Barbus barbus and Cyprinus carpio attained 3.40, 3.66 and 3.80 respectively. Modal chromosome number was 2n = 48-50 for diploid individuals and 2n = 100-104 for phylogenetically tetraploid ones. In all the species 5--8% of the genome is represented by highly repetitive and foldback DNA. In DNA reassociation kinetics of phylogenetically tetraploid Cyprinidae a distinct plateau separates an intermediate reassociating sequence fraction (about 22% of the genome; with average repetition frequencies between 1,000 and 1,400) from a slow reassociating one (unique DNA; about 72% of the genome). These two genome fractions are not clearly distinguishable from each other in Cot curves of the diploid Cyprinidae, where a similar plateau is not evident. Since simple ploidy changes are not expected to affect DNA reassociation kinetics we suggest a different evolution in the genome organization of the two ploidy groups. Some possible hypotheses are discussed.