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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.

We provide cytogenetic data for the threatened species Gymnogeophagus setequedas, and the first record of that species collected in the Iguaçu River, within the Iguaçu National Park's area of environmental preservation, which is an unexpected occurrence for that species. We verified a diploid number of 2n = 48 chromosomes (4sm + 24st + 20a) and the presence of heterochromatin in centromeric and pericentromeric regions, which are conserved characters in the Geophagini. The multiple nucleolar organizer regions observed in G. setequedas are considered to be apomorphic characters in the Geophagini, whereas the simple 5S rDNA cistrons located interstitially on the long arm of subtelocentric chromosomes represent a plesiomorphic character. Because G. setequedas is a threatened species that occurs in lotic waters, we recommend the maintenance of undammed environments within its known area of distribution.Keywords: Chromosomes, Conservation, Iguaçu River, Karyotype, Paraná River.Fornecemos dados citogenéticos para a espécie ameaçada Gymnogeophagus setequedas, e o primeiro registro da espécie coletado no rio Iguaçu, na área de preservação ambiental do Parque Nacional do Iguaçu, a qual é uma área de ocorrência inesperada para esta espécie. Verificamos em G. setequedas 2n = 48 cromossomos (4sm + 24st + 20a) e heterocromatina presente nas regiões centroméricas e pericentroméricas, as quais indicam caracteres conservados em Geophagini. Múltiplas regiões organizadoras de nucléolos foram observadas em G. setequedas e são consideradas características apomórficas em Geophagini, enquanto cístrons de DNAr 5S simples e localizados intersticialmente no braço longo de cromossomos subtelocêntricos representam uma característica plesiomórfica. Visto que G. setequedas é uma espécie ameaçada de extinção que ocorre em águas lóticas, recomendamos a manutenção de ambientes livre de barragens em sua área de distribuição.

This study provides new insight into the chromosomal diversification in Loricariinae. We analyzed nine species from different Brazilian hydrographic basins, using conventional and molecular cytogenetic methods, aiming to understand the karyotypic diversification, and contribute with cytotaxonomic markers in this group considered one of the most diverse of Loricariidae. Our results evidenced a high karyotypic variability in diploid number (2n) ranging from 2n = 54 (Loricariichthys platymetopon and Loricariichthys anus), 2n = 60 (Rineloricaria reisi and Rineloricaria parva), 2n = 62 (Proloricaria prolixa), 2n = 64 (Loricaria cataphracta complex species), 2n = 66 (Sturisoma barbatum), and 2n = 68 (Pyxiloricaria menezesi). Different patterns of 18S and 5S ribosomal DNA (rDNA) were also identified, while slight divergences in heterochromatin distribution were observed. This high variability is probably related with independent events of Robertsonian translocations, pericentric inversions, and different mechanisms of rDNA sites dispersion (nonreciprocal translocation and transposable element [TEs] co-localization). In addition, our study provides a set of efficient chromosomal markers for the characterization of all analyzed species, and certainly, in future analyzes, will contribute as a useful cytotaxonomic tool in groups where the traditional taxonomy based on morphological data are not sufficient to clarify their relationship.

Karyotype and chromosomal characteristics of both minor and major rDNA of

A cytogenetic analysis was performed on four populations of Hypostomus strigaticeps from the Paraná River basin, Brazil. Two populations were collected from the large channel river at the Itaipu reservoir area and the other two were from the upper stretches of tributaries of the Paraná River. All populations showed 2n=72 chromosomes (12m+12sm+18st+30a), intra- and interpopulation 18S rDNA site polymorphisms (two to three acrocentric chromosome pairs), and multiple 5S rDNA sites in three chromosome pairs (4, 21, and 28). C-banding revealed heterochromatin located in the centromere and pericentromere regions of most chromosome; however, large heterochromatic blocks (CMA3(-)/DAPI(+)) on the long arm of acrocentric chromosomes identified intra- and interpopulation polymorphism. The amount and distribution of heterochromatin seem to be correlated to biogeographical characteristics of H. strigaticeps along the Paraná River. Morphometric results also showed diversity among the populations, suggesting phenotypic plasticity of this species. Evolutionary, taxonomy, and biogeographical approaches with regard to H. strigaticeps and interrelationships in Hypostomus are discussed.

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The karyotype and chromosomal characteristics of Trachydorasparaguayensis, a representative of the South American catfish family Doradidae, were analyzed by conventional (Giemsa staining, silver staining, C-banding) and molecular (FISH with rDNA and telomeric probes) cytogenetic techniques. The diploid chromosome number was 2n = 56, with 36 metacentric, 16 submetacentric, and 4 subtelocentric chromosomes in both sexes; however, a remarkable heteromorphism in pair 22 (submetacentric and metacentric elements) was detected in 6 individuals. Compared to other representatives of Doradidae which mostly have 58 chromosomes, the karyotype of T. paraguayensis suggests a reduction in 2n due to chromosomal fusion, as could be deduced from the presence of an interstitial telomere sequence in the submetacentric pair 19. Pale heterochromatic blocks were present in the terminal regions of some chromosomes, very similar to other species of Doradidae. The interstitial position of the NORs observed in the karyotype of T. paraguayensis differs from those reported for most Doradidae species, indicating that it is a derived character. FISH with 5S rDNA revealed 2 interstitial fluorescent signals in the submetacentric pair 22, and the polymorphism of these sites likely resulted from a pericentric inversion.