Luiz Antonio Carlos Bertollo

A biodiversity approach in the neotropical Erythrinidae fish, Hoplias malabaricus. Karyotypic survey, geographic distribution of cytotypes and cytotaxonomic considerations

Hoplias malabaricus, a widely distributed neotropical freshwater fish, shows a conspicuous karyotypic diversification. An overview of this diversity is presented here comprising several Brazilian populations, and some others from Argentina, Uruguay and Surinam. Seven general cytotypes are clearly identified on the basis of their diploid number (2n=39 to 2n=42), chromosomal morphology and sex chromosome systems, which can be clustered into two major karyotypic groups. This clustering suggests that karyotype structure would be more informative than the diploid number regarding cytotype relationships in this fish group. While some cytotypes show a wide geographical distribution, some others appear to be endemic to specific hydrographic basins. Sympatric cytotypes can occur without detection of hybrid forms; this situation points to a lack of gene flow, a fact that is also reinforced by studies with genomic markers. The karyotypic data support the view that the nominal taxon H. malabaricus corresponds to a species complex comprising distinct evolutionary units, each with well-established chromosomal differences.

An XX/XY Sex Chromosome System in a Fish Species, Hoplias malabaricus, with a Polymorphic NOR-Bearing X Chromosome

Cytogenetic studies were carried out in the fish, Hoplias malabaricus, from the Parque Florestal do Rio Doce (Brazil). This population is characterized by 2n = 42 chromosomes for both males and females and an XX/XY sex chromosome system, confirmed through several banding methods. Females show 24 metacentric, 16 submetacentric and 2 subtelocentric chromosomes. Males show 24 metacentric, 17 submetacentric and 1 subtelocentric chromosomes. While the X chromosome is easily recognized (the only subtelocentric element), the Y chromosome is somewhat difficult to identify but appears to correspond to the smallest submetacentric in the male karyotype. In-situ hybridization with an 18S rDNA probe showed 10 well-labeled chromosomes, including the X chromosome. The 5S rDNA is interstitially located in a single metacentric pair independent of the 18S rDNA sites. The NOR on the X chromosome is always active and occurs adjacent to a heterochromatic distal segment on the long arm. Variations in size of the NORs and/or heterochromatic segment correspond to a polymorphic size condition observed in the X chromosome. The present results confirm the XX/XY sex chromosome system in the population analyzed as well as a new cytotype in the Hoplias malabaricus group.

Nucleolar Organizing Regions, 18S and 5S rDNA in Astyanax Scabripinnis (Pisces, Characidae): Populations Distribution and Functional Diversity

Astyanax scabripinnis specimens from four distinct populations in Brazil were studied with respect to their karyotype macrostructure, nucleolar organizer regions, and 18S and 5S rRNA genes. The four populations showed a 2n = 50 chromosomes (3 M + 11 SM + 5 ST + 6 A pairs) and 1–2 B chromosomes. No chromosomal differentiations were observed between sexes. Although a karyotypic diversity has been characterized in this fish group, the populations now analyzed presented the same macrokaryotypic pattern. Chromosome mapping of 5S rDNA showed a total of eight sites located in four distinct chromosomal pairs, with no apparent differences among populations. A comparative study on 18S rDNA locations and Ag-NORs showed some secondary NOR sites that are not usually expressed in karyotypes and a probable differential NOR activity among populations. Correlations between these data, environmental conditions and B chromosomes are discussed.

Chromosome spreading of associated transposable elements and ribosomal DNA in the fish Erythrinus erythrinus. Implications for genome change and karyoevolution in fish

BackgroundThe fish, Erythrinus erythrinus, shows an interpopulation diversity, with four karyomorphs differing by chromosomal number, chromosomal morphology and heteromorphic sex chromosomes. Karyomorph A has a diploid number of 2n = 54 and does not have differentiated sex chromosomes. Karyomorph D has 2n = 52 chromosomes in females and 2n = 51 in males, and it is most likely derived from karyomorph A by the differentiation of a multiple X1X2Y sex chromosome system. In this study, we analyzed karyomorphs A and D by means of cytogenetic approaches to evaluate their evolutionary relationship.ResultsConspicuous differences in the distribution of the 5S rDNA and Rex3 non-LTR retrotransposon were found between the two karyomorphs, while no changes in the heterochromatin and 18S rDNA patterns were found between them. Rex3 was interstitially dispersed in most chromosomes. It had a compartmentalized distribution in the centromeric regions of only two acrocentric chromosomes in karyomorph A. In comparison, in karyomorph D, Rex3 was found in 22 acrocentric chromosomes in females and 21 in males. All 5S rDNA sites co-localized with Rex3, suggesting that these are associated in the genome. In addition, the origin of the large metacentric Y chromosome in karyomorph D by centric fusion was highlighted by the presence of internal telomeric sites and 5S rDNA/Rex3 sites on this chromosome.ConclusionWe demonstrated that some repetitive DNAs (5S rDNA, Rex3 retroelement and (TTAGGG)n telomeric repeats) were crucial for the evolutionary divergence inside E. erythrinus. These elements were strongly associated with the karyomorphic evolution of this species. Our results indicate that chromosomal rearrangements and genomic modifications were significant events during the course of evolution of this fish. We detected centric fusions that were associated with the differentiation of the multiple sex chromosomes in karyomorph D, as well as a surprising increase of associated 5S rDNA/Rex3 loci, in contrast to karyomorph A. In this sense, E. erythrinus emerges as an excellent model system for better understanding the evolutionary mechanisms underlying the huge genome diversity in fish. This organism can also contribute to understanding vertebrate genome evolution as a whole.

Distribution of sex chromosome mechanisms in neotropical fish and description of a ZZ/ZW system in Parodon hilarii (Parodontidae)

SUMMARYParodon hilarii, a neotropical fish species of the family Parodontidae, presents a well-differentiated ZZ/ZW system, with a W chromosome being the largest in the complement and mostly heterochromatic. A review of the sex chromosome of neotropical fish is presented and some aspects of their differentiation are discussed, with emphasis on the family Parodontidae.

Short term culture from solid tissues of fishes

SUMMARYIn fish cytogenetics the methods of chromosome preparations still need to be improved in order to obtain good metaphase figures for banding technics and more accurate analysis. In this paper we describe a very fast and simples culture method from solid fish tissues. Results of its application to different species as well as about 5-BrdU incorporation, both for chromosome banding and sister chromatid differentiation are reported. The data emphasized the advantage of this short term culture method wich provide excellent chromosome preparations suitables for basic and applied cytogenetic studies.

Cytogenetic Considerations on the Genus Astyanax (Pisces, Characidae). I. Karyotypic Variability

SUMMARYA study was carried out on mitotic and meiotic chromosomes of four species of the genus Astyanax (Pisces, Characidae) from three different water basins in the State of Sao Paulo, Brazil. The following karyotypic characteristics were observed: A. bimaculatus, 2n = 50 (n = 25, FN = 86–88); A. fasciatus, 2n = 46 (n = 23, FN = 90); « A. fasciatus » from the Juquia river, 2n = 48 (n = 24, FN = 94); A. schubarti, 2n = 36 (n = 18, FN = 70) and A. scabripinnis paranae, 2n = 50 (n = 25, FN = 90–92). The diversity in the number and morphology of the chromosomes suggests a model of non-conservative karyotypic evolution in this genus, with chromosome rearrangements of the centric fusion/fission type and/or inversion playing an important role in these alterations. On the basis of its characteristics, A. schubarti has the most differentiated karyotype and, in view of the low diploid number and small number of subtelocentric-acrocentric chromosomes, is probably of most recent origin. The two karyotypes encountere...

The X1X2Y sex chromosome system in the fish Hoplias malabaricus. I. G-, C- and chromosome replication banding

Hoplias malabaricus, a widely distributed neotropical fish (Central America to Argentina), may represent a group of distinct species showing diversified cytotypes with respect to chromosome number, morphology and sex systems. One of these karyotypic forms is characterized by an X1X1X2X2/X1X2Y sex chromosome system, with 2n= 40 and 39 chromosomes in females and males respectively. Analyses with G-, C- and chromosome replication banding permitted a better characterization of the sex chromosomes in this cytotype. The Y chromosome, unique in males, resulted from a translocation event between two biarmed chromosomes: one similar to chromosome 6 (X1) and the other one similar to chromosome 20 (X2), the latter corresponding to a probable identification. On the basis of the observed banding patterns, the Y chromosome may represent a stable dicentric, with an inactive centromere interstitially located on its long arm. The results are also related to a specific satellite DNA subfamily, previously characterized in Hoplias malabaricus, which appears to be associated with the X1 chromosome.

Characterization of eight species of Anostomidae (Cypriniformes) fish on the basis of the nucleolar organizing region

SUMMARYThe present study shows the distribution of nucleolar organizing regions (NORs) in eight species of fresh-water fish of family Anostomidae belonging to the genera Leporinus, Leporellus and Schizodon, using silver staining techniques. Only two NORs per karyotype were encountered in all the species investigated. Despite the karyotypic similarity of these species, NORs appear in distinct chromosome and/or positions, thus representing excellent cytologic markers.

Evidence for a System of Supernumerary Chromosomes in Prochilodus Scrofa Steindachner, 1881 (Pisces, Prochilodontidae)

SUMMARYBoth males and females of the fish Prochilodus scrofa have a diploid number of 2n = 54. However, with the exception of a single female, all 59 specimens (25 ♀, 34 ♂) studied had 1–5 minutes accessory chromosomes. The unstable behavior of these chromosomes during mitosis and meiosis as well as their heterochromatic nature, as detected by C-banding, are characteristics that emphasize their supernumerary nature. This is the first report of chromosomes of this type in the Osteichthyes (Pisces).