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Populations of seven Ancistrus species were analyzed from streams and rivers of three hydrographic Brazilian basins. All populations showed diferent diploid numbers (2n), fundamental numbers (FNs), and karyo-types. Some representatives of Loricariidae have 2n = 54 chromosomes, which is very likely an ancestral cytotaxonomic characteristic, but many other representatives show extensive karyotype diversiication. In the Ancistrus species studied, extensive karyotypic differentiation, which is generally associated with chromosome number reduction and rearrangement of the ribosomal RNA gene (rDNA) sites, was verified. Chromosomal locations of 18S and 5S rDNA were jointly detected using fluorescence in situ hybridization (FISH). In all the Ancistrus species analyzed, 18S rDNA sites were detected only on one chromosome pair, though this differed among species. 5S rDNA was located on 1-3 chromosome pairs either separately or in synteny with 18S rDNA in four of the seven species/populations. Hence the karyotype differentiation in Ancistrus species could be associated with a morphological speciation process, suggesting that chromosome fusions, inversions, deletions, duplications, and heterochromatination could contribute to the karyotype evolution of these neotropical armored catfishes. [ABSTRACT FROM AUTHOR]

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 H. regani from the Piracicaba and Tietê River Basins are also discussed. The occurrence of H. 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. [ABSTRACT FROM AUTHOR]

The freshwater silver catfish from the genus Rhamdia belongs to a group of neotropical fish with wide distribution throughout Central and South America. The results obtained in the F1 generation of native specimens of this species bred in captivity using molecular cytogenetic tools revealed a high number of triploid specimens (46.8%) in the samples analyzed. The use of double fluorescent in situ hybridization (double-FISH) with 18S and 5S rDNA probes allowed highlighting the location of ribosomal sites with independent activity. This chromosome marker allowed the identification of triploid nuclei, in which three markers were visualized, in contrast to diploid fish, which only exhibited two fluorescent signals. As triploid specimens exhibit either total or partial gonad sterility, the present study demonstrates the importance of cytogenetic monitoring in restocking programs aimed at genetic conservation. [ABSTRACT FROM AUTHOR]

Chromosome analyses were carried out for several fish species in a region impacted by the connection between two hydrographic basins, where a river originally pertaining to the Paraná River basin was transposed to the São Francisco River basin in the state of Minas Gerais, Brazil. The purpose was to assess the dispersal of invasive species from one hydrographic basin to the other and the consequent new geographical distributions of species that had been previously isolated from each other. Species of the families Parodontidae ( Apareiodon piracicabae, A. ibitiensis, Parodon hilarii, and P. nasus), Sternopygidae ( Eigenmannia virescens), and Gymnotidae ( Gymnotus sylvius) were studied. The four species of Parodontidae had 2n = 54 chromosomes, but species-specific karyotype structures, including the presence of the ZZ/ZW sex chromosome system in A. ibitiensis and P. hilarii. Two distinct karyomorphs (A and B) were identified for E. virescens, although with the same diploid number (2n = 38 chromosomes). G. sylvius had 2n = 40 chromosomes. P. hilarii and E. virescens (karyomorph B) are considered to be native to the São Francisco River basin, whereas A. piracicabae, A. ibitiensis, E. virescens (karyomorph A), and G. sylvius are known for the Paraná River basin, and P. nasus is known for the Paraná-Paraguay basin. The presence of the last five species in the São Francisco River basin indicates that they migrated from the Parana River to the São Francisco River basin due to the transposition of the river, and can therefore be considered invasive species in this basin. Moreover, a natural migratory pathway through the former wetland may have affected this dispersal. [ABSTRACT FROM AUTHOR]

Genetic variations in Astyanax sp. fish from Vila Velha State Park and Tibagi river (Paraná, Brazil) were analyzed by RAPD. Intrapopulational genetic similarity was analyzed at three collection sites. The higher RAPD polymorphism observed at site 3 (Tibagi river) suggests either an overlapping of structured populations or the presence of coexisting morphotypes at this site. Significant p values obtained by homogeneity tests revealed an unequal loci proportion among populations. The significance of similarity coefficients indicated that the differences observed among populations are relevant. These findings provide important information for the management and conservation of the species analyzed and for genetic variability maintenance programs. [ABSTRACT FROM AUTHOR]

B chromosomes are extra genomic compounds found in different taxonomic groups, including plants and animals. Obtaining patterns of resolutive chromosomal bands is necessary to understand the nuclear organization, variability and nature of B chromosome chromatin and possible transcriptional regions. In this study, we analyzed 35 Astyanax scabripinnis specimens sampled from Fazenda Lavrinha, a stream in the Paraíba do Sul river basin, Brazil. Through the incorporation of the thymidine analog 5'-bromo-2'-deoxyuridine (5-BrdU) in vivo , it was possible to recognize the replicating regions of the B chromosome at the beginning of the S phase, differentially characterized in relationship to the regions of late replication. In this perspective, it is possible to suggest that the B chromosome of this species possesses a territory and the chromatin accessible for transcription, especially in the light (i.e., early replicating) bands (p1.1; p1.3; and p2.1 and q1.1, q1.3, q2.1, and q2.2). The late-replicating regions are corresponding to the blocks of constitutive heterochromatin. They show a preferential accumulation of satellite DNA As 51. By the use of the fluorochrome chromomycin A3 (CMA3), it was possible to identify GC-rich chromosomal regions, corresponding to late-replicating parts of genome, confirming the revealed data by the replication banding and C-banding. In addition, the analysis by confocal microscopy in kidney cells indicates the location of a peripheral anchorage of this chromosome in the nuclear lamina, reinforcing the idea of downregulation of the associated regions.

Electric fish of the order Gymnotiformes are endemic to the Neotropical region, and their highest diversity is observed in the Amazon region. The family Gymnotidae, which consists of the genera Electrophorus and Gymnotus , is a natural group and is located at the base of the phylogeny of the order. Gymnotus is a widely distributed and specious genus with high karyotypic diversity, especially concerning to the diploid number and the locations of repetitive sequences. Our karyotyping results in five species of the family Gymnotidae ( Gymnotus ucamara , Gymnotus cf. stenoleucus , Gymnotus cf. pedanopterus , Gymnotus mamiraua , and Gymnotus carapo "Maranhão") corroborate the proposal of plasticity of the diploid number in this group. Moreover, in this study, we propose that the 5S ribosomal DNA (rDNA) sequences were species-specific markers that act as a potential biogeographical marker for the genus. Besides, the sequence's location, particularly in G . mamiraua from Central Amazon, shows a close relationship with 5S of the Gymnotus species, with 54 chromosomes, from the Paraná-Paraguay basin in the Center-South of Brazil. Considering that the ancestral diploid number for Gymnotidae is 52 chromosomes, we also suggest that the trend in the family is toward a decrease in the chromosome number. However, the carapo clade stands out in this regard, with an increase and a decrease in chromosome number; this pattern may be reinforced with the ecologic behaviors and the geodispersal patterns of this clade.

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.

The family Ariidae comprises approximately 130 catfish species on both warm-temperate and tropical continental shelves around the world. The systematics of the group is problematic, with several misidentification problems. In order to better understand the evolutionary relationships in the family, the present study used a cytogenetic approach to characterize two populations of Genidens genidens and two populations of Aspistor luniscutis from the southern coast of Brazil using conventional techniques and fluorescent in situ hybridization with 18S rDNA probes. The two species had the same diploid number (2n = 56), high fundamental numbers and similar banding patterns, thereby corroborating the karyotypic homogeneity proposed for the group. Single nucleolus organizer regions (NORs) were found in the genus Genidens and multiple NORs were found in Aspistor, which are considered an important cytotaxonomic marker for this genus. Karyotypic evolution trends were hypothesized, providing a better understanding of the karyotype diversity and chromosome evolution processes., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Smooth pufferfish of the family Tetraodontidae had become pure genomic models because of the remarkable compaction of their genome. This trait seems to be the result of DNA loss following its divergence from the sister family Diodontidae, which possess larger genomes. In this study, flow cytometry was used for estimate the genome size of four pufferfish species from the Neotropical region. Cytogenetic data and confocal microscopy were also used attempting to confirm relationships between DNA content and cytological parameters. The haploid genome size was 0.71 + or - 0.03 pg for Sphoeroides greeleyi, 0.34 + or - 0.01 pg for Sphoeroides spengleri, 0.82 + or - 0.03 pg for Sphoeroides testudineus (all Tetraodontidae), and 1.00 + or - 0.03 pg for Chilomycterus spinosus (Diodontidae). These differences are not related with ploidy level, because 46 chromosomes are considered basal for both families. The value for S. spengleri represents the smallest vertebrate genome reported to date. Since erythrocyte cell and nuclear sizes are strongly correlated with genome size, the variation in this last is considered under both adaptive and evolutionary perspectives.