Orlando Moreira Filho

Altitudinal variation for B chromosome frequency in the characid fish Astyanax scabripinnis

The analysis of three populations of the characid fish Astyanax scabripinnis located at different altitudes along the same stream has revealed the presence of a macro B chromosome in two high-altitude populations (1800 m and 1920 m) but its absence from a low-altitude population (700 m). Because the stream flows through very rugged mountains, with numerous falls ensuring that any gene flow occurs downstream only, the absence of B chromosomes from the low-altitude populations is best interpreted in the light of the parasitic theory of B chromosome evolution. Under this theory, we would expect B chromosomes to be more frequent where environmental conditions are more favourable for the species, because Bs are best tolerated there. The widespread presence of these B chromosomes in numerous Brazilian river headwaters, which are the preferred habitat for this species, support this possibility.

Morphological Differentiation and Possible Origin of B Chromosomes in Natural Brazilian Population of Astyanax Scabripinnis (PISCES, CHARACIDAE)

Specimens of Astyanax scabripinnisfrom three different altitudes (1920, 1800 and 700 m) along the Ribeirão Grande stream in the Campos do Jordão region (São Paulo State, Brazil) were investigated. The same diploid number, 2n = 50, was detected in the three populations, with the following karyotypic constitution: 6M, 22SM, 10ST and 12A. The populations located at 1920 and 1800 m altitude presented a high incidence of B chromosomes varying in number (0–2), shape (meta- and submetacentrics), size (large and small) and sex-related frequency (they were more frequent among females). The two morphologically variant B chromosomes probably evolved from a metacentric macrochromosome, which is the most commonly observed B chromosome in several A. scabripinnispopulations.

Chromosomal localization of 5S and 18S rRNA genes in three Parodon species (Pisces, Parodontidae)

Abstract The nucleolar organizer regions (NORs) have often been analyzed in Parodontidae fish using silver staining. In the genus Parodon, the Ag-NORs are used as species chromosomal markers, while in the genus Apareiodon they show a more conserved location. In the present study, the NORs are investigated in three Parodon species (P. hilarii, Parodon sp. and P. tortuosus) using silver and fluorochrome staining and fluorescence in situ hybridization (FISH) with a PCRobtained 18S probe. In addition, the chromosomal 5S rDNA sites are also analyzed with a cloned 5S rDNA probe. It was seen a close correspondence between Ag-NORs, chromomycin positive regions and the 18S rDNA sites in the chromosomes of the three species. A major and a minor 5S rDNA cluster were also abserved in these species. While the 18S and major 5S rRNA genes are located on different chromosome pairs in Parodon sp. and P. hilarii, they are linked in P. tortuosus, although in opposite regions of the chromosome. Both 18S and 5S rDNA sites appear as important chromosome markers for Parodon species.

First description of B chromosomes in the family Auchenipteridae, Parauchenipterus galeatus (Siluriformes) of the São Francisco River basin (MG, Brazil)

B chromosomes are considered additional and non-essential; they likely originate from A chromosomes and follow a distinct evolution. In fish, approximately half of the Neotropical species with B chromosomes are Characiformes and 35% are Siluriformes. There has been no report of B chromosomes in Auchenipteridae until this moment. B chromosomes found in a population of Parauchenipterus galeatus from the São Francisco River basin in the state of Minas Gerais (Brazil) were small, metacentric, totally heterochromatic and exhibited intra-individual and inter-individual variation. The diploid number was 58 chromosomes (22 metacentric, 16 submetacentric, 12 subtelocentric and 8 acrocentric). The nucleolar organizing regions were simple and the heterochromatin intercalated in the ribosomal sites, characterized by CMA(3) and DAPI fluorochromes, was of a GC-rich constitution. The 5S rDNA genes were located in an intercalary position in only one chromosome pair. An hypothesis about the origin of the B chromosomes in P. galeatus and a review on B chromosomes in catfish are also presented in this study.

Constitutive heterochromatin, 5S and 18S rDNA genes in Apareiodon sp. (Characiformes, parodontidae) with a ZZ/ZW sex chromosome system

Karyotype, sex chromosome system and cytogenetics characteristics of an unidentified species of the genus Apareiodon originating from Piquiri River (Paraná State, Brazil) were investigated using differential staining techniques (C-banding and Ag-staining) and fluorescent in situ hybridization (FISH) with 5S and 18S rDNA probes. The diploid chromosome number was 2n = 54 with 25 pairs of meta- (m) to submetacentric (sm) and 2 pairs of subtelocentric (st) chromosomes. The major ribosomal rDNA sites as revealed by Ag-staining and FISH with 18S rDNA probe were found in distal region of longer arm of st chromosome pair 26, while minor 5S sites were observed in the interstitial sites on chromosome pairs 2 (smaller cluster) and 7 (larger one). The C-positive heterochromatin had pericentromeric and telomeric distribution. The heteromorphic sex chromosome system consisted of male ZZ (pair 21) and female middle-sized m/st Z/W chromosomes. The pericentric inversion of heterochromatinized short arm of ancestral Z followed by multiplication of heterochromatin segments is hypothesized for origin of W chromosome. The observed karyotype and chromosomal markers corresponded to those found in other species of the genus.

Cytogenetical analyses in three fish species of the genus Pimelodus(Siluriformes: Pimelodidae) from rio São Francisco: considerations about the karyotypical evolution in the genus

Karyotypes and other chromosomal markers were investigated in three species of the catfish genus Pimelodus, namely P. fur, P. maculatus and Pimelodus sp., from municipality of Tres Marias, Minas Gerais, Brazil, using differential staining techniques (C-banding, Silver nitrate and CMA3 staining). The diploid chromosome number was 2n = 56 in P. maculatus and Pimelodus sp., while in P. fur 2n = 54. The karyotype of P. fur consisted in 32M + 8SM + 6ST + 8A with fundamental number (NF) of 100, that of P. maculatus 32M + 12SM + 12A with NF = 112, and that of Pimelodus sp. had 32M + 12Sm + 6ST + 6A with NF = 106.The nucleolar organizer regions (NORs) in all three species were invariably detected in telomeres of longer arm of the 20th chromosome pair. These sites were also positive after CMA3 and C-banding. No heteromorphic sex chromosomes were detected and C-banding pattern was species specific. Inferences about the karyotype differentiation in Pimelodus and putative chromosomal rearrangements are hypohesized.

Characterization of invasive fish species in a river transposition region: evolutionary chromosome studies in the genus Hoplias (Characiformes, Erythrinidae)

Karyotypic analyses were performed in fishes from the genus Hoplias (H.malabaricus and H. lacerdae groups) from the São Francisco River basin (Brazil), in an impacted region by a river transposition which altered the local ecology and fish fauna. The karyotypes were investigated using chromosomal markers obtained from classic and molecular cytogenetics (Giemsa, CMA3 and DAPI staining, C-banding, Ag-NORs, and FISH with 18S rDNA, 5S rDNA and 5SHindIII satellite DNA probes). Two karyotypic forms were found for the H. malabaricus group—karyomorph F, corresponding to the native form from the São Francisco River basin, and karyomorph A, corresponding to the invading form from the Upper Paraná River basin. Specimens from the H. lacerdae group exhibited striking chromosome differences in relation to the H. malabaricus group, thereby enabling good cytotaxonomic characterization and inferences regarding the karyotype evolution of these groups.

Physical mapping of the 18S and 5S ribosomal genes in nine Characidae species (Teleostei, Characiformes)

Characidae is one of the largest fish families of the Neotropical region, and presenting a pronounced morphological variability, certainly does not constitute a monophyletic group. The cytogenetical data also show a large chromosomal variation and can provide important information for a better understanding of the relationships between the species of this group. 18S and 5S rDNA probes were used in the present study for the chromosomal mapping in different Characidae species from the Sao Francisco River (Astyanax lacustris, Astyanax scabripinnis, Hasemania nana, Piabina argentea, Orthospinus franciscensis, Serrapinnus heterodon, Serrapinnus piaba and Myleus micans) and Alto Parana (Astyanax altiparanae) basins. Species with a single pair of chromosomes bearing the nucleolar organizing regions (NORs) were identified, as well as species with multiple NORs, up to a maximum of seven 18S rDNA sites. The number of 5S rDNA site was also not constant, varying from two to eight. The mapping of the ribosomal genes was useful for the characterization and differentiation of the analyzed species.

A poorly known case of watershed transposition between the São Francisco and upper Paraná river basins

During construction of the Furnas hydroelectric power dam in the upper rio Parana basin in the early 1960s, the rio Piumhi drainage outflow was diverted into the headwaters of the Sao Francisco river basin. The rio Piumhi was a right bank tributary of the rio Grande, which unites with the rio Paranaiba to form the rio Parana. The transposition allowed the entire fish fauna of the rio Piumhi and associated swamps, lakes, and tributaries to intermingle with the fish fauna of the Sao Francisco basin via the ribeirao Sujo, a right bank tributary of the Sao Francisco. The transposition of the watershed may have had a major impact on the current composition of the fish fauna of the upper rio Sao Francisco watershed.

Karyotypic diversity between allopatric populations of the group Hoplias malabaricus (Characiformes: Erythrinidae): evolutionary and biogeographic considerations

Three populations of the group Hoplias malabaricus from the hydrographic basins of the Sao Francisco, Araguaia/Tocantins and Xingu Rivers in Brazil were analyzed using classic cytogenetic methods (Giemsa staining, C-banding and Ag-NORs) and molecular methods (fluorescent in situ hybridization with 18S rDNA, 5S rDNA and 5SHindIII satellite DNA probes). The chromosome markers allowed the characterization of these populations as belonging to karyomorph A and the detection of inter-population divergences. These differences likely stem from different evolutionary histories resulting from geographic isolation between populations associated to the dispersive mode of these organisms, reinforcing genetic diversity in the group Hoplias malabaricus.