Cytogenetic characterization of Hypostomus soniae Hollanda-Carvalho & Weber, 2004 from the Teles Pires River, southern Amazon basin: evidence of an early stage of an XX/XY sex chromosome system

In the present study, we analyzed individuals of Hypostomus soniae (Loricariidae) collected from the Teles Pires River, southern Amazon basin, Brazil. Hypostomus soniae has a diploid chromosome number of 2n = 64 and a karyotype composed of 12 metacentric (m), 22 submetacentric (sm), 14 subtelocentric (st), and 16 acrocentric (a) chromosomes, with a structural difference between the chromosomes of the two sexes: the presence of a block of heterochromatin in sm pair No. 26, which appears to represent a putative initial stage of the differentiation of an XX/XY sex chromosome system. This chromosome, which had a heterochromatin block, and was designated proto-Y (pY), varied in the length of the long arm (q) in comparison with its homolog, resulting from the addition of constitutive heterochromatin. It is further distinguished by the presence of major ribosomal cistrons in a subterminal position of the long arm (q). The Nucleolus Organizer Region (NOR) had different phenotypes among the H. soniae individuals in terms of the number of Ag-NORs and 18S rDNA sites. The origin, distribution and maintenance of the chromosomal polymorphism found in H. soniae reinforced the hypothesis of the existence of a proto-Y chromosome, demonstrating the rise of an XX/XY sex chromosome system.

Chromosomal Diversity of Three Species of Hypostomus Lacépède, 1803 (Siluriformes, Loricariidae), from the Paraná River Basin, Brazil: A Species Complex in Hypostomus ancistroides Reinforced by a ZZ/ZW Sex Chromosome System

Hypostomus shows wide morphological patterns, corroborated by great chromosomal diversity that has suggested the existence of new species, especially from small tributaries. Cytogenetic analysis has contributed to estimate a cryptic diversity providing important data for taxonomic and evolutionary studies. Cytogenetic techniques were carried out on species from a small tributary of Ivaí River, Keller River (upper Paraná River basin): Hypostomus aff. ancistroides, Hypostomus topavae, and Hypostomus aff. hermanni that presented 2n = 68, 80, and 72 chromosomes, respectively. Each species showed the same diploid number from previous descriptions for other populations but different karyotype formulas, and Hypostomus aff. ancistroides had a ZZ/ZW sex chromosome system. Multiple NORs (nucleolar organizer regions) and pericentromeric heterochromatin blocks were found in the three species. Moreover, each of them showed species-specific heterochromatins. Multiple 5S rDNA sites were detected in Hypostomus aff. ancistroides and H. topavae, whereas Hypostomus aff. hermanni had only one pair bearing these sites. In addition to the divergence in the karyotype formulas, chromosomal markers used showed karyotype differences in the three species related to other respective populations studied. Furthermore, the first description of a ZZ/ZW system for Hypostomus aff. ancistroides reinforces the hypothesis that it may correspond to a species complex and yet, confirming an unknown cryptic diversity existent in small rivers.

Karyotypic diversity of the armoured catfish genus Hypostomus (Siluriformes: Loricariidae) in the context of its occurrence and distribution

This study taxonomically reviewed the specimens studied by Artoni & Bertollo (1996) and assimilated species of Hypostomus into three groups according to their cytogenetic characteristics, vagility and occurrence environments.

Cytogenetic characterization of species of the family Heptapteridae (Teleostei: Siluriformes) from the Cuiabá and Ivaí River Basins, Brazil

We cytogenetically characterized three species of Heptapteridae (Pimelodella sp, Pimelodella taenioptera, and Imparfinis schubarti) by investigating the distribution of constitutive heterochromatin and nucleolar organizer regions by silver nitrate impregnation (Ag-NOR) and fluorescence in situ hybridization. Pimelodella sp showed had a diploid number (2n) = 46 chromosomes, 26m + 10sm + 10st, and FN = 92; P. taenioptera, 2n = 52 chromosomes, 26m + 22sm + 4st, and FN = 104; and I. schubarti, 2n = 58 chromosomes, 28m + 28sm + 2st, and FN = 116. The two Pimelodella species had Ag-NORs sites on the submetacentric pair 14, located on the short arm in terminal position. In I. schubarti, the Ag-NORs sites were in an interstitial position on the long arm of the metacentric pair 1. C-banding revealed that Pimelodella sp contained a small amount of constitutive heterochroma-tin, whereas P. taenioptera contained a higher number of heterochromatic regions, in the pericentromeric, interstitial, and telomeric positions. I. schubarti had markers in centromeric and telomeric regions of a few chromosomes, and a large pericentromeric block on pair 1. Fluorochrome chromomycin A3 (CMA3) staining revealed positive signals on pair 14 in both Pimelodella species. Treatment with 4ꞌ,6-diamidino- 2-phenylindole (DAPI) revealed no markings in P. taenioptera, but an interstitial marking on the long arm of pair 14 in Pimelodella sp. In I. schubarti, positive signals of CMA3 were detected in the first pair, but negative signals were detected for DAPI staining. These results con-tribute to the karyotypic description of the less-studied species in the Brazilian Midwest.

Cytogenetic analysis of two locariid species (Teleostei, Siluriformes) from Iguatemi River (Parana River drainage) in Brazil

Fishes of the Loricariidae family, known as "cascudos", constitute an endemic group in Neotropical freshwaters. In this study, were cytogenetically examined two species of Loricariidae (Pterygoplichthysanisitsi Eigenmann & Kennedy, 1903 and Farlowellaamazonum (Günther, 1864) belonging to Hypostominae and Loricariinae subfamilies respectively) from Iguatemi River. Our study provide the first description regarding C-band and fluorochromic analysis in Farlowellaamazonum. In Farlowellaamazonum, diploid number was 58 chromosomes, with single Ag-NOR and heterochromatic blocks in centromeric regions of some chromosomes and large subtelomeric blocks were evidenced on the long arm of the pair 27, being this region CMA3 (+)/DAPI(-). The Pterygoplichthysanisitsi showed diploid number equal 52 chromosomes, with single Ag-NOR and heterochromatic blocks in centromeric and telomeric regions of some chromosomes and conspicuous large telomeric blocks on the long arm of the pair 10, being this region CMA3 (+)/DAPI(-). The results show that karyotype formula is nonconservative in Pterygoplichthysanisitsi and Farlowellaamazonum.

B chromosome and NORs polymorphism in Callichthys callichthys (Linnaeus, 1758) (Siluriformes: Callichthyidae) from upper Paraná River, Brazil

B chromosomes are extra chromosomes from the normal chromosomal set, found in different organisms, highlighting their presence on the group of fishes. Callichthys callichthys from the upper Paraná River has a diploid number of 56 chromosomes (26 m-sm + 30 st-a) for both sexes, with the presence of a sporadically acrocentric B chromosome. Moreover, one individual presented a diploid number of 57 chromosomes, with the presence of a morphologically ill-defined acrocentric B chromosome in all analyzed cells. The physical mapping of 5S and 18S rDNA shows multiple 5S rDNA sites and only one pair of chromosomes with 18S sites in C. callichthys, except for two individuals. These two individuals presented a third chromosome bearing NORs (Ag-staining and 18S rDNA) where 5S and 18S rDNA genes are syntenic, differing only in position. The dispersion of the 18S rDNA genes from the main st-achromosome pair 25 to one of the chromosomes from the m-sm pair 4 would have originated two variant individuals, one of which with the ill-defined acrocentric B chromosome. Mechanisms to justify the suggested hypothesis about this B chromosome origin are discussed in the present study.

Polymorphisms of the nucleolus organizing regions in Loricaria cataphracta (Siluriformes, Loricariidae) of the upper Paraguay River basin indicate an association with transposable elements

A cytogenetic analysis of Loricaria cataphracta revealed a diploid number of 2n = 64 chromosomes, distributed as 12 metacentric + 8 submetacentric + 2 subtelocentric + 42 acrocentric, with a fundamental number of 86. Analysis of the nucleolus organizing region (NOR) using silver nitrate impregnation and fluorescence in situ hybridization (18S rDNA probe) techniques showed intra-population chromosomal polymorphism that could be classified into five different patterns (I to V), involving four pairs of chromosomes (8, 9, 12, and 13). In pattern I, the NOR was located in pair 12, whereas in pattern II, the NOR was detected in pair 8; these two patterns were characterized as a simple-NOR system. A multiple NOR system was evident in the other patterns (III, IV, and V). In pattern III, the NOR was located in only one of the homologs of pairs 12 and 8, and in patterns IV and V, the NOR was observed in pair 12 and in only one of the homologs of pairs 9 and 13, respectively. In addition, C-band analysis also showed this pattern of variation, and characterized a polymorphism in relation to the constitutive heterochromatin; the composition of this region was GC-rich (positive CMA3) and 4',6-diamidino-2-phenylindole negative. Transposition of NOR sites for mobile elements is suggested to explain this polymorphism.

Cytogenetic analysis of Astyanax laticeps (Cope, 1894) (Ostariophysi: Characidae) from the laguna dos Patos system

The genus Astyanax is prominent among Characiformes, due to the large number of species found and its wide geographic distribution. In this work, Astyanax laticeps specimens from the laguna dos Patos system were cytogenetically analyzed. A diploid number of 2n = 50 chromosomes distributed into 6m+16sm+16st+12a (FN = 88) was found, without differences between males and females. A few small heterochromatin blocks were observed, besides three more conspicuous C-bands, corresponding to NORs, as confirmed by silver nitrate and CMA3 staining, FISH, and DAPI negative staining. These regions were located in a medium-sized subtelocentric and in a large subtelocentric chromosomal pair, probably because of a deletion of this region in one homologous chromosome, or due to a transposition event between them.

Cytogenetic characterization of Crenicichla (Pisces, Perciformes, Cichlidae) of the Iguaçu River

Three populations of the genus Crenicichla, namely Crenicichla iguassuensis, Crenicichla sp 1 and Crenicichla sp 2, from the Iguaçu River, were analyzed cytogenetically, and their nucleolus organizer regions, constitutive heterochromatin distribution and chromomycin A3 markings were studied. Karyotype analyses showed a diploid number of 48 chromosomes, made up of 2 metacentric pairs, 2 submetacentric pairs, 7 subtelocentric pairs, and 13 acrocentric pairs for the three Crenicichla species and no sexual chromosome differentiation. Nucleolus organizer regions showed strong interstitial marking on the first chromosome pair, coincident with a constriction presented by Giemsa and positive marking by chromomycin. Although constitutive heterochromatin patterns were also similar, with pericentromeric markings, small differences in the three species could be observed. Crenicichla sp 2 presented some chromosomes with bitelomeric markings absent in Crenicichla iguassuensis and Crenicichla sp 1.

Cytogenetic analysis and description of the sexual chromosome determination system ZZ/ZW of species of the fish genus Serrapinnus (Characidae, Cheirodontinae)

Four populations of Serrapinnus notomelas and one population of Serrapinnus sp.1, both belonging to the subfamily Cheirodontinae, were analyzed by Giemsa and silver nitrate impregnation techniques. We found 2n = 52 chromosomes for all populations, with interspecific differences in the karyotype formula; S. notomelas showed 16 m + 22 sm + 10 st + 4a, with fundamental number (FN) = 100 for males, and 16 m + 23 sm + 10 st + 3a, with FN = 101 for females. Serrapinnus sp.1 had 8m + 16 sm + 4 st + 24 a, with FN = 80 for males, and 8m + 15 sm + 4 st + 25 a, with FN = 79 for females. The difference in FN for the two sexes is due to a pair of heteromorphic chromosomes in the females of both species, which characterizes a ZZ/ZW-type mechanism of chromosome sexual determination. Interspecies differences were also found in nucleolus organizer regions (NORs). A simple NOR system was detected in three of four S. notomelas populations, while Serrapinnus sp.1 had two chromosome pairs with NOR. Although S. notomelas and Serrapinnus sp.1 have the same diploid number, differences in the karyotype structure indicate that these are different species. Apparently there was pericentric inversion during the karyotype evolution of these species.

Sympatric occurrence of three cytotypes and four morphological types of B chromosomes of Astyanax scabripinnis (Pisces, Characiformes) in the River Ivaí Basin, state of Paraná, Brazil

Chromosomes of Astyanax scabripinnis from the Tatupeba stream, Ivaí Basin (state of Paraná, Brazil), were analyzed. Astyanax scabripinnis population presents 3 different diploid numbers (2n = 46, 48 and 50) and B chromosomes in each cytotype. Eighty per cent of the females among individuals of cytotype I (2n = 50) has a metacentric B macrochromosome, whereas three different types of B chromosomes were identified in individuals of cytotype II (2n = 48). Cytotype III (2n = 46) showed two B chromosomes of different morphologic types (metacentric macrochromosomes and acrocentric) in all specimens and cells analyzed. Constitutive heterochromatin pattern for the three cytotypes showed weak markings in centromeric regions and conspicuous blocks in the telomere regions of ST and A chromosomes. Whereas C-banding showed that B chromosomes were totally or partially heterochromatic, a discussion on their behavior and origin was also undertaken.

Study on karyotype and occurrence of B chromosomes in two endemic species of the genus Pimelodus (Siluriformes, Pimelodidae) from the river Igua çu

The current work describes, for the first time, the occurrence of B chromosomes in the genus Pimelodus. Cytogenetic analysis in P. ortmanni and Pimelodus sp., from the river Iguaçu basin, revealed a diploid number of 56 chromosomes. Whereas distribution pattern of C-banding in Pimelodus sp. showed predominance of heterochromatin at the two extremities of several pairs of chromosomes, centromere markings predominated in P. ortmanni. Additional chromosomes in the two species were observed with numerical intra-individual variations between zero and four B, together with interspecies differences in their frequency. In Giemsa-stained metaphases two distinct morphological types of B chromosomes were identified: Bm (B metacentric) and Ba (B acrocentric). In P. ortmanni both types of B chromosomes were totally heterochromatic; the Bm type in Pimelodus sp. had heterochromatin throughout its entire extension; the Ba type was partially heterochromatic with telomere markings on the long arm.

A natural triploid in Trichomycterus davisi (Siluriformes, Trichomycteridae): mitotic and meiotic characterization by chromosome banding and synaptonemal complex analyses

Within a total of 50 analyzed specimens a male individual of Trichomycterus davisi has been recorded with 81 chromosomes including 60 metacentric, 18 submetacentric and three subtelocentric chromosomes. When compared with diploid individuals (2n = 54) and the morphological standard of chromosomes, this male is a triploid with 3n = 81 chromosomes. Since staining with silver nitrate indicates three active nucleolar organizer regions (NORs), the three NOR-bearing chromosomes in this individual are genetically active. Analysis of the synaptonemal complex (SC) by electronic microscopy shows that there is an incomplete pairing of the third set of chromosomes in the triploid individual.

Intra-individual numerical chromosomal polymorphism in Trichomycterus davisi (Siluriformes, Trichomycteridae) from the Iguaçu River basin in Brazil

Cytogenetic analysis of Trichomycterus davisi, collected from the Iguaçu River basin, has shown a diploid number of 2n = 54 chromosomes. However, we observed intra-individual numerical polymorphism in a T. davisi specimen. There were three cell populations with diploid number 2n = 54 (40M + 12SM + 2ST), 2n = 55 (40M + 12SM + 2ST + 1M) and 2n = 56 (40M + 12SM + 2ST + 2A) chromosomes. This variation was attributed to a probable post-zygotic non-disjunction of a metacentric chromosome of small/middle size, followed by centric fission, which originated in this individual.

Karyotype characterization of three species of the genus Trichomycterus (Teleostei, Siluriformes) from Iguaçu river basin

Three species belonging to the genus Trichomycterus were collected from Iguaçu river basin and analyzed from the cytogenetic point of view. Although the species studied had the same diploid number 2n = 54 chromosomes and fundamental number 108, they differed in their karyotypic formulae. C-band patterns showed presence of specific-species markers in T. davisi and T. stawiarski. Results of analysis from the nucleolus organizer region, obtained by silver nitrate staining and CMA3, showed that size heteromorphism observed in this region may be due to gene duplication. Evolution aspects of the Trichomycteridae family and the presence of B chromosome in T. davisi are discussed.

Cytogenetic and morphometric differences in populations of Astyanax "scabripinnis" (Pisces, Characidae) from Maringá region, PR, Brazil

A cytogenetic and morphometric study of four populations of characid fish assigned to the "complex" of Astyanax scabripinnis originating from three riverine basins, namely Ivaí (populations A and B), Paranapanema (C) and Paraná (D), was carried out. Karyological analysis showed the diploid chromosome number 2n = 48 for population B and 2n = 50 for the remaining populations. All populations under study differed in the composition of karyotypes and C-banding patterns. Canonical variable analysis used to assess the morphometric data revealed that 1) the four populations under study were entirely discriminated from each other and 2) the coefficients that most contributed to this pattern were standard length, rostrodorsal distance, eye diameter and snout length. The results indicate that the differences in karyotypes were paralleled by the morphological differentiation of the populations under study and contributed to the problem of systematics of A. scabripinnis "complex".