Against the mainstream: exceptional evolutionary stability of ZW sex chromosomes across the fish families Triportheidae and Gasteropelecidae (Teleostei: Characiformes).

Teleost fishes exhibit a breath-taking diversity of sex determination and differentiation mechanisms. They encompass at least nine sex chromosome systems with often low degree of differentiation, high rate of inter- and intra-specific variability, and frequent turnovers. Nevertheless, several mainly female heterogametic systems at an advanced stage of genetic differentiation and high evolutionary stability have been also found across teleosts, especially among Neotropical characiforms.

Centric Fusions behind the Karyotype Evolution of Neotropical Pencilfishes (Characiforme, Lebiasinidae): First Insights from a Molecular Cytogenetic Perspective.

Lebiasinidae is a Neotropical freshwater family widely distributed throughout South and Central America. Due to their often very small body size, Lebiasinidae species are cytogenetically challenging and hence largely underexplored. However, the available but limited karyotype data already suggested a high interspecific variability in the diploid chromosome number (2), which is pronounced in the speciose genus , a popular taxon in ornamental fish trade due to its remarkable body coloration.

Deciphering the Evolutionary History of Arowana Fishes (Teleostei, Osteoglossiformes, Osteoglossidae): Insight from Comparative Cytogenomics.

Arowanas (Osteoglossinae) are charismatic freshwater fishes with six species and two genera ( and ) distributed in South America, Asia, and Australia. In an attempt to provide a better assessment of the processes shaping their evolution, we employed a set of cytogenetic and genomic approaches, including i) molecular cytogenetic analyses using C- and CMA/DAPI staining, repetitive DNA mapping, comparative genomic hybridization (CGH), and Zoo-FISH, along with ii) the genotypic analyses of single nucleotide polymorphisms (SNPs) generated by diversity array technology sequencing (DArTseq). We observed diploid chromosome numbers of 2 = 56 and 54 in and , respectively, and 2 = 50 in while and presented 2 = 48 and 44, respectively.

Cytogenetics, genomics and biodiversity of the South American and African Arapaimidae fish family (Teleostei, Osteoglossiformes).

Osteoglossiformes represents one of the most ancestral teleost lineages, currently widespread over almost all continents, except for Antarctica. However, data involving advanced molecular cytogenetics or comparative genomics are yet largely limited for this fish group. Therefore, the present investigations focus on the osteoglossiform family Arapaimidae, studying a unique fish model group with advanced molecular cytogenetic genomic tools.

Karyotype diversity and evolutionary trends in the Asian swamp eel Monopterus albus (Synbranchiformes, Synbranchidae): a case of chromosomal speciation?

Background: Synbranchidae or swamp eels are fishes belonging to the order Synbranchiformes that occur in both freshwater and occasionally in brackish. They are worldwide distributed in tropical and subtropical rivers of four different continents. A large degree of chromosomal variation has been found in this family, mainly through the use of conventional cytogenetic investigations.

Emerging patterns of genome organization in Notopteridae species (Teleostei, Osteoglossiformes) as revealed by Zoo-FISH and Comparative Genomic Hybridization (CGH).

Notopteridae (Teleostei, Osteoglossiformes) represents an old fish lineage with ten currently recognized species distributed in African and Southeastern Asian rivers. Their karyotype structures and diploid numbers remained conserved over long evolutionary periods, since African and Asian lineages diverged approximately 120 Mya. However, a significant genetic diversity was already identified for these species using molecular data.

Chromosomes of Asian cyprinid fishes: cytogenetic analysis of two representatives of small paleotetraploid tribe Probarbini.

Background: Polyploidy, although still poorly explored, represents an important evolutionary event in several cyprinid clades. Herein, and - representatives of the paleotetraploid tribe Probarbini, were characterized both by conventional and molecular cytogenetic methods.

Results: Alike most other paleotetraploid cyprinids (with 2n = 100), both species studied here shared 2n = 98 but differed in karyotypes: displayed 18m + 34sm + 46st/a; NF = 150, while exhibited 26m + 14sm + 58st/a; NF = 138.

Early Stages of XY Sex Chromosomes Differentiation in the Fish (Characiformes, Erythrinidae) Revealed by DNA Repeats Accumulation.

Background: Species with 'young' or nascent sex chromosomes provide unique opportunities to understand early evolutionary mechanisms (e.g. accumulation of repetitive sequences, cessation of recombination and gene loss) that drive the evolution of sex chromosomes.

Sex Chromosome Evolution and Genomic Divergence in the Fish (Characiformes, Erythrinidae).

The Erythrinidae family (Teleostei: Characiformes) is a small Neotropical fish group with a wide distribution throughout South America, where corresponds to the most widespread and cytogenetically studied taxon. This species possesses significant genetic variation, as well as huge karyotype diversity among populations, as reflected by its seven major karyotype forms (i.e.

First Chromosomal Analysis in Hepsetidae (Actinopterygii, Characiformes): Insights into Relationship between African and Neotropical Fish Groups.

Hepsetidae is a small fish family with only the genus , with six described species distributed throughout the South, Central and Western regions of Africa, showing a close relationship with the Alestidae and some Neotropical fish families. However, no cytogenetic information is available for both Hepsetidae and Alestidae species, thus preventing any evolutionary comparative studies at the chromosomal level. In the present study, we are providing new cytogenetic data for , including the standard karyotype, C-banding, repetitive DNAs mapping, comparative genomic hybridization (CGH) and whole chromosome painting (WCP), providing chromosomal patterns and subsidies for comparative cytogenetics with other characiform families.

Tracking the evolutionary pathway of sex chromosomes among fishes: characterizing the unique XX/XYY system in Hoplias malabaricus (Teleostei, Characiformes).

The Neotropical fish, Hoplias malabaricus, is one of the most cytogenetically studied fish taxon with seven distinct karyomorphs (A-G) comprising varying degrees of sex chromosome differentiation, ranging from homomorphic to highly differentiated simple and multiple sex chromosomes. Therefore, this fish offers a unique opportunity to track evolutionary mechanisms standing behind the sex chromosome evolution and differentiation. Here, we focused on a high-resolution cytogenetic characterization of the unique XX/XYY multiple sex chromosome system found in one of its karyomorphs (G).

Comparative cytogenetics in three Sciaenid species (Teleostei, Perciformes): evidence of interspecific chromosomal diversification.

Background: Species belonging to the Sciaenidae family present a karyotype composed by 48 acrocentric chromosomes and are thus considered a striking example of chromosomal conservation. In this family, three species are extensively studied including , and due to their importance in fishery and aquaculture in East Asia. Despite abundant data of population genetics available for some of them, cytogenetic information on these species is still scarce and obtained by conventional cytogenetic protocols.

Chromosomal Evolution in Lower Vertebrates: Sex Chromosomes in Neotropical Fishes.

Fishes exhibit the greatest diversity of species among vertebrates, offering a number of relevant models for genetic and evolutionary studies. The investigation of sex chromosome differentiation is a very active and striking research area of fish cytogenetics, as fishes represent one of the most vital model groups. Neotropical fish species show an amazing variety of sex chromosome systems, where different stages of differentiation can be found, ranging from homomorphic to highly differentiated sex chromosomes.

Evolutionary Relationships and Cytotaxonomy Considerations in the Genus Pyrrhulina (Characiformes, Lebiasinidae).

Although fishes exhibit the greatest biodiversity among the vertebrates, a large percentage of this fauna is still underexplored on evolutionary cytogenetic questions, particularly the miniature species. The Lebiasinidae family is a particular example for such case. This study is the first one presenting differential cytogenetic methods, such as C-banding, repetitive DNAs mapping, comparative genomic hybridization (CGH), and whole chromosome painting in lebiasinid 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.

Karyotype and Mapping of Repetitive DNAs in the African Butterfly Fish Pantodon buchholzi, the Sole Species of the Family Pantodontidae.

The monophyletic order Osteoglossiformes represents one of the most ancestral groups of teleosts and has at least 1 representative in all continents of the southern hemisphere, with the exception of Antarctica. However, despite its phylogenetic and biogeographical importance, cytogenetic data in Osteoglossiformes are scarce. Here, karyotype and chromosomal characteristics of the lower Niger River population of the African butterfly fish Pantodon buchholzi, the sole species of the family Pantodontidae (Osteoglossiformes), were examined using conventional and molecular cytogenetic approaches.

Chromosome mapping of repetitive DNAs in sergeant major fishes (Abudefdufinae, Pomacentridae): a general view on the chromosomal conservatism of the genus.

Species of the Abudefduf genus (sergeant-majors) are widely distributed in the Indian, Pacific and Atlantic oceans, with large schools inhabiting rocky coastal regions and coral reefs. This genus consists of twenty recognized species are of generalist habit, showing typical characteristics of colonizers. Some populations maintain gene flow between large oceanic areas, a condition that may influence their cytogenetic features.

W Chromosome Dynamics in Triportheus Species (Characiformes, Triportheidae): An Ongoing Process Narrated by Repetitive Sequences.

Characterizing the abundance and genomic distribution of repetitive DNAs provides information on genome evolution, especially regarding the origin and differentiation of sex chromosomes. Triportheus fishes offer a useful model to explore the evolution of sex chromosomes, since they represent a monophyletic group in which all species share a ZZ/ZW sex chromosome system. In this study, we analyzed the distribution of 13 classes of repetitive DNA sequences by FISH, including microsatellites, rDNAs, and transposable elements in 6 Triportheus species, in order to investigate the fate of the sex-specific chromosome among them.

Repetitive DNAs highlight the role of chromosomal fusions in the karyotype evolution of Dascyllus species (Pomacentridae, Perciformes).

The Dascyllus genus consists of 11 species spread over vast regions of the Indo-Pacific, showing remarkable reductions in the diploid chromosome numbers (2n). The present study analyzed the karyotypes and other chromosomal characteristics of D. trimaculatus (2n = 48; 2st + 46a; NF = 50), D.

Hypermethylated Chromosome Regions in Nine Fish Species with Heteromorphic Sex Chromosomes.

Sites and amounts of 5-methylcytosine (5-MeC)-rich chromosome regions were detected in the karyotypes of 9 Brazilian species of Characiformes fishes by indirect immunofluorescence using a monoclonal anti-5-MeC antibody. These species, belonging to the genera Leporinus, Triportheus and Hoplias, are characterized by highly differentiated and heteromorphic ZW and XY sex chromosomes. In all species, the hypermethylated regions are confined to constitutive heterochromatin.

Genomic organization of repetitive DNAs highlights chromosomal evolution in the genus Clarias (Clariidae, Siluriformes).

Background: The genus Clarias (Clariidae, Siluriformes) contains at least 61 species naturally spread over vast regions of Asia, India and Africa. However, Clarias species have also been introduced in many different countries and represent the most widespread catfishes in the world. These fishes are also known as "walking catfishes" due to their ability to move over land.

Comparative cytogenetics in the genus Hoplias (Characiformes, Erythrinidae) highlights contrasting karyotype evolution among congeneric species.

Background: The Erythrinidae fish family contains three genera, Hoplias, Erythrinus and Hoplerythrinus widely distributed in Neotropical region. Remarkably, species from this family are characterized by an extensive karyotype diversity, with 2n ranging from 39 to 54 chromosomes and the occurrence of single and/or multiple sex chromosome systems in some species. However, inside the Hoplias genus, while H.

Genomic Organization of Repetitive DNA Elements and Its Implications for the Chromosomal Evolution of Channid Fishes (Actinopterygii, Perciformes).

Channid fishes, commonly referred to as "snakeheads", are currently very important in Asian fishery and aquaculture due to the substantial decline in natural populations because of overexploitation. A large degree of chromosomal variation has been found in this family, mainly through the use of conventional cytogenetic investigations. In this study, we analyzed the karyotype structure and the distribution of 7 repetitive DNA sequences in several Channa species from different Thailand river basins.

Genomic organization of repetitive DNAs and its implications for male karyotype and the neo-Y chromosome differentiation in Erythrinus erythrinus (Characiformes, Erythrinidae).

Studies have demonstrated the effective participation of repetitive DNA sequences in the origin and differentiation of the sex chromosomes in some biological groups. In this study several microsatellites and retrotranposable sequences were cytogenetically mapped in the Erythrinus erythrinus (Bloch & Schneider, 1801) male genome (karyomorph C), focusing on the distribution of these sequences in the sex chromosomes and in the evolutionary processes related to their differentiation. Males of E.

Chromosomal mapping of repetitive DNAs in Triportheus trifurcatus (Characidae, Characiformes): insights into the differentiation of the Z and W chromosomes.

Repetitive DNA sequences play an important role in the structural and functional organization of chromosomes, especially in sex chromosome differentiation. The genus Triportheus represents an interesting model for such studies because all of its species analyzed so far contain a ZZ/ZW sex chromosome system. A close relationship has been found between the differentiation of the W chromosome and heterochromatinization, with the involvement of different types of repetitive DNA in this process.