Chromosome complements of Channalucius and C.striata from Phu Quoc Island and karyotypic evolution in snakehead fishes (Actinopterygii, Channidae).

Snakehead fishes of the family Channidae are obligatory air-breathers freshwater predators, the vast majority of which belong to the genus Channa Scopoli, 1777. Channa species are characterized by high karyotypic diversity due to various types of chromosomal rearrangements. It is assumed that, in addition to the lifestyle, fragmentation and isolation of snakehead populations contribute to an increase in karyotypic diversity. However, the chromosome complements of many isolated populations of widespread Channa species remain unknown, and the direction of karyotype transformations is poorly understood. This paper describes the previously unstudied karyotypes of Channalucius (Cuvier, 1831) and C.striata (Bloch, 1793) from Phu Quoc Island and analyzes the trends of karyotypic evolution in the genus Channa. In C.lucius, the karyotypes are differed in the number of chromosome arms (2n = 48, NF = 50 and 51), while in C.striata, the karyotypes are differed in the diploid chromosome number (2n = 44 and 43, NF = 48). A comparative cytogenetic analysis showed that the main trend of karyotypic evolution of Channa species is associated with a decrease in the number of chromosomes and an increase in the number of chromosome arms, mainly due to fusions and pericentric inversions. The data obtained support the assumption that fragmentation and isolation of populations, especially of continental islands, contribute to the karyotypic diversification of snakeheads and are of interest for further cytogenetic studies of Channidae.

Extensive karyotype variability of African fish genus Nothobranchius (Cyprinodontiformes).

Karyotypes of 65 species of the genus Nothobranchius Peters, 1868 were reviewed and of those 35 examined first time. The results of present study have shown that fishes of the genus Nothobranchius possessed highly diverse karyotypes. The diploid chromosome number (2n) ranged from 16 to 50. The most frequent 2n was 2n = 36 (in 35 species) while the second one 2n = 38 (in 13 species). Proportion of biarmed chromosomes varied from 0 to 95% between species. Diploid chromosome number variability apparently exists as a result of chromosomal fusions or fissions and extensive karyotypic formula alterations promoting by inversions. Multiple sex chromosomes of system X1X1X2X2/X1X2Y type were found only in karyotypes of 5 species. The extensive karyotype variability, unusual for teleosts, of genus Nothobranchius can be likely associated with the characteristics of its life cycle and inhabiting under unstable environment of East African savannah temporal pools.

Morphologically Cryptic Species of the Astyanax bimaculatus "Caudal Peduncle Spot" Subgroup Diagnosed Through Cytogenetic Characters.

Astyanax is a species-rich polyphyletic genus distributed between the southern United States and central Argentina. The genus contains groups of cryptic species, which are difficult to distinguish, and are sometimes identified wrongly. Basic and molecular cytogenetic analyses were run on Astyanax abramis and three junior synonyms of Astyanax lacustris: Astyanax altiparanae, from the upper Paraná River basin, Astyanax asuncionensis, from the lower Paraná basin, and Astyanax jacuhiensis, from the upper Uruguay River. These species all belong to the Astyanax bimaculatus group. All species presented 2n = 50 chromosomes and single nucleolar organizing regions (NORs). In A. altiparanae, the karyotype was 6m + 28sm+4st+12a and the NORs were present in pair 20, while A. jacuhiensis was 8m + 28sm+6st+8a, with NORs in pair 22, and A. asuncionensis was 8m + 24sm+6st+12a, with NORs in pair 20. A. abramis was 4m + 30sm+8st+8a with NORs in pair 22. Fluorescence in situ hybridization revealed single 5S rDNA cistrons in A. altiparanae and A. asuncionensis, and multiple (4) cistrons in A. abramis and A. jacuhiensis. Heterochromatin had a distinct distribution in each species, but was predominantly centromeric and interstitial proximal. In A. abramis and A. asuncionensis, the first acrocentric chromosome pair presented centromeric, telomeric, and interstitial-proximal heterochromatin in the long arm, which may represent the presence of homologous chromosomes in these species. While there are some cytogenetic similarities, differences in the location of 5S rDNA, distribution of heterochromatin, and karyotype formulae contribute to the differentiation of the study species, and support the identification of phylogenetically proximate groups in the "Astyanax clade."

Evolutionary dynamics of an at-rich satellite DNA and its contribution to karyotype differentiation in wild diploid Arachis species.

Satellite DNA (satDNA) is a major component of the heterochromatic regions of eukaryote genomes and usually shows a high evolutionary dynamic, even among closely related species. Section Arachis (genus Arachis) is composed of species belonging to six different genomes (A, B, D, F, G and K). The most distinguishing features among these genomes are the amount and distribution of the heterochromatin in the karyotypes. With the objective of gaining insight into the sequence composition and evolutionary dynamics of the heterochromatin fraction in Arachis, we investigated here the sequence diversity, genomic abundance, and chromosomal distribution of a satDNA family (ATR-2) among seven diploid species of section Arachis. All of the isolated sequences were AT-rich and highly conserved at both intraspecific and interspecific levels, without any species-specific polymorphism. Pairwise comparisons of isolated ATR-2 monomers revealed that most of the nucleotide sites were in the first two transitional stages of Strachan's model. However, the abundance of ATR-2 was significantly different among genomes according to the 'library hypothesis'. Fluorescent in situ hybridization revealed that ATR-2 is a main component of the DAPI+ centromeric heterochromatin of the A, F, and K genomes. Thus, the evolution of the different heterochromatin patterns observed in Arachis genomes can be explained, at least in part, by the differential representation of ATR-2 among the different species or even among the chromosomes of the same complement. These findings are the first to demonstrate the participation of satDNA sequences in the karyotype diversification of wild diploid Arachis species.

Dynamics of Rex3 in the genomes of endangered Iberian Leuciscinae (Teleostei, Cyprinidae) and their natural hybrids.

BACKGROUND: Iberian Leuciscinae are greatly diverse comprising taxa of hybrid origin. With highly conservative karyotypes, Iberian Chondrostoma s.l. have recently demonstrated sub-chromosomal differentiation and rapid genome restructuring in natural hybrids, which was confirmed by ribosomal DNA (rDNA) transposition and/or multiplication. To understand the role of repetitive DNAs in the differentiation of their genomes, a genetic and molecular cytogenetic survey was conducted in Achondrostoma oligolepis, Anaecypris hispanica, Iberochondrostoma lemmingii, I. lusitanicum, Pseudochondrostoma duriense, P. polylepis, Squalius pyrenaicus and hybrids between A. oligolepis x (P. duriense/P. polylepis), representing 'alburnine', chondrostomine and Squalius lineages. RESULTS: Partial Rex3 sequences evidenced high sequence homology among Leuciscinae (≥98 %) and different fish families (80-95 %) proposing a relatively recent activity of these elements in the species inspected. Low nucleotide substitution rates (<20 %) and intact ORFs suggests that Rex3 may in fact be active in these genomes. The chromosomal distribution of Rex3 retroelement was found highly concentrated at pericentromeric and moderately at subtelomeric blocks, co-localizing with 5S rDNA loci, and correlating with blocks of heterochromatin and C0t-1 DNA. This accumulation was evident in at least 10 chromosome pairs, a pattern that seemed to be shared among the different species, likely pre-dating their divergence. Nevertheless, species-specific clusters were detected in I. lusitanicum, P. duriense, P. polylepis and S. pyrenaicus demonstrating rapid and independent differentiation. Natural hybrids followed the same patterns of accumulation and association with repetitive sequences. An increased number of Rex3 clusters now associating also with translocated 45S rDNA clusters vouched for other genomic rearrangements in hybrids. Rex3 sequence phylogeny did not agree with its hosts' phylogeny but the observed distribution pattern is congruent with an evolutionary tendency to protect its activity, a robust regulatory system and/or events of horizontal transfer. CONCLUSIONS: This is the first report directed at retroelement physical mapping in Cyprinidae. It helped outlining conceivable ancestral homologies and recognizing retrotransposon activation in hybrids, being possibly associated with genome diversification within the subfamily. The extensive diversity of Iberian Leuciscinae makes them excellent candidates to explore the processes and mechanisms behind the great plasticity distinguishing vertebrate genomes.

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.

Comparative cytogenetics of Neotropical cichlid fishes (Nannacara, Ivanacara and Cleithracara) indicates evolutionary reduction of diploid chromosome numbers.

A comparative cytogenetic analysis was carried out in five species of a monophyletic clade of neotropical Cichlasomatine cichlids, namely Cleithracara maronii Steindachner, 1881, Ivanacara adoketa (Kullander & Prada-Pedreros, 1993), Nannacara anomala Regan, 1905, N. aureocephalus Allgayer, 1983 and N. taenia Regan, 1912. Karyotypes and other chromosomal characteristics were revealed by CDD banding and mapped onto the phylogenetic hypothesis based on molecular analyses of four genes, namely cyt b, 16S rRNA, S7 and RAG1. The diploid numbers of chromosomes ranged from 44 to 50, karyotypes were composed predominantly of monoarmed chromosomes and one to three pairs of CMA3 signal were observed. The results showed evolutionary reduction in this monophyletic clade and the cytogenetic mechanisms (fissions/fusions) were hypothesized and discussed.

Chromosome polymorphism of heterochromatin and nucleolar regions in two populations of the fish Astyanax bockmanni (Teleostei: Characiformes)

Karyotype and other chromosomal markers as revealed by C-banding and silver (Ag) impregnation in two Astyanax bockmanni populations (Barra Seca Stream and Campo Novo River) were examined. The diploid chromosome number 2n = 50 and nearly identical karyotypes were documented. C-banding revealed heterochromatic blocks on the terminal regions of some chromosomes, with high frequencies of polymorphisms. The Ag-impregnation showed that the nucleolus organizer regions (NORs) varied in number, location and organization. Astyanax bockmanni revealed chromosome characteristics similar those of the species complex "A. scabripinnis". Mechanisms that may be responsible for the high degree of polymorphism are discussed.

Cariótipo e outros marcadores cromossômicos revelados pelo bandamento C e impregnação da prata (Ag) em duas populações de Astyanax bockmanni (córrego Barra Seca e rio Campo Novo) foram examinados. O número cromossômico diploide 2n = 50 e cariótipo quase idênticos são documentados. Bandamento C revelou blocos heterocromáticos na região terminal de alguns cromossomos, com um elevado nível de polimorfismos. A impregnação da prata mostrou variabilidade do número, posição e organização para as regiões organizadoras de nucléolo (RONs). Astyanax bockmanni revelou características cromossômicas similares ao complexo "A. scabripinnis" e os mecanismos responsáveis pelo alto nível do polimorfismo foram discutidos.

Comparative cytogenetics of Carnegiella marthae and Carnegiella strigata (Characiformes, Gasteropelecidae) and description of a ZZ/ZW sex chromosome system

Comparative cytogenetic analyses of hatchetfishes Carnegiella marthae and Carnegiella strigata (Gasteropelecidae) from the Rio Negro basin were performed using conventional Giemsa staining, silver (Ag) -staining and C-banding. The diploid chromosome numbers of both species equaled 2n = 50 but their karyotypes were distinct. We found evidence for sex chromosomes in C. marthae since karyotype of males presented 20 M + 12 SM + 4 ST + 14 A and ZZ ST chromosomes while the females presented 20 M + 12 SM + 4 ST + 14 A and ZW ST chromosomes of distinct size. Conversely, C. strigata presented 4 M + 4 SM + 2 ST + 40 A chromosomes without sex chromosome heteromorphism. Karyotypes of both species had two NOR-bearing SM chromosomes of distinct size indicating the presence of multiple NOR phenotypes. The sex chromosome pair had specific C-banding pattern allowing identification of both Z and W. This heteromorphic system has previously been described for the gasteropelecids.