Cytogenetic characterization of Hypostomus nigromaculatus (Siluriformes: Loricariidae)

Abstract

Hypostomus is the most speciose genus in the family Loricariidae, with approximately 120 species. These fish show a wide morphological and color variation, which hinders the identification of species, mainly of widely distributed representatives. The aim of this study was to contribute to the current knowledge on cytogenetic features of Hypostomus nigromaculatus. Three specimens of H. nigromaculatus, collected in two tributaries of rio Tibagi, Paraná, and in Cachoeira de Emas, rio MogiGuaçu, São Paulo, the latter being the type locality of H. nigromaculatus, were studied. Chromosomal preparations were submitted to Giemsa staining, silver nitrate impregnation, C-banding and CMA 3 and DAPI fluorochromes staining. All samples presented 2n = 76, but the rio Mogi-Guaçu sample differed from those from tributaries of rio Tibagi in relation to karyotype formulae, distribution and composition of heterochromatin, and NOR location. The silver nitrate staining revealed the presence of multiple Ag-NORs for all samples, but with differences on the location on chromosomes. CMA 3 staining reveled bright signals equivalent to NOR-bearing chromosomal segments; such sites were characterized by negative, i.e. unstained, marks after DAPI staining. The pattern of heterochromatin distribution was distinctive among samples from rio Mogi-Guaçu and tributaries of rio Tibagi. The differences observed between the sample from rio Mogi-Guaçu and the ones from tributaries of rio Tibagi allow us to suggest that these samples are presently isolated. Further analyses are necessary to ascertain whether such isolation refers to distinct populations or characterizes true different species.O gênero Hypostomus é um dos mais especiosos na família Loricariidae, tendo aproximadamente 120 espécies. Apresenta uma ampla diversidade quanto ao padrão de coloração e morfologia, o que dificulta a identificação de determinadas espécies, principalmente aquelas com ampla distribuição geográfica. Para isso os dados obtidos neste trabalho contribuem para os estudos citogenéticos de Hypostomus nigromaculatus. Foram analisados três exemplares de H. nigromaculatus de afluentes do rio Tibagi, Paraná e Cachoeira de Emas, rio Mogi-Guaçu, São Paulo, sendo esta última, a localidade tipo de H. nigromaculatus. Os cromossomos foram submetidos à coloração convencional (Giemsa), impregnação por nitrato de prata, bandamento-C e coloração com os fluorocromos CMA 3 e DAPI. Todos os exemplares apresentaram 2n = 76, no entanto com diferença quanto às fórmulas cariotípicas, distribuição e composição da heterocromatina. O nitrato de prata detectou RONs múltiplas para as amostras, porém com diferenças quanto à localização nos cromossomos. A coloração com fluorocromo CMA 3 foi correspondente aos cromossomos Ag-RONs, na coloração com DAPI foram observadas bandas negativas, ou seja, não coradas. O padrão de distribuição da heterocromatina foi diferente para as amostras do rio Mogi-Guaçu e dos tributários do rio Tibagi. As diferenças observadas entre as amostras de rio Mogi-Guaçu e afluent...

Karyotype structure of Hypostomus cf. plecostomus (Linnaeus, 1758) from Tapajós River basin, Southern Amazon: occurrence of sex chromosomes (ZZ/ZW) and their evolutionary implications

“…The standard C band observed in H. cf. plecostomus with a few conspicuous blocks on the long arm of the chromosome as well as on the short arms of other chromosomes, was also found in other species of the genus, such as H. affinis (Kavalco et al, 2004), H. nigromaculatus (Rubert et al, 2008), and H. cochliodon (Cereali et al, 2008). This corroborates the results of Artoni and Bertollo (1996) and Kavalco et al (2004), who reported that Hypostomus has relatively little constitutive heterochromatin.…”

Population divergence and peculiar karyoevolutionary trends in the loricariid fish Hypostomus aff. unae from northeastern Brazil

“…unae analyzed in the present study. However, the latter also presented GC-rich NORs as shown by CMA 3 + signals, following the general pattern among Hypostominae (Rubert et al, 2008).…”

“…A co-localization of NORs and heterochromatin is commonly reported for Hypostomus (Rubert et al, 2008). However, this correspondence is not a ubiquitous condition inasmuch as it is absent in some loricariids such as Upsilodus sp, Neoplecostomus microps Steindachner, 1877 (Kavalco et al, 2005) and population C of H. aff.…”

Chromosomal diversity in Hypostomus (Siluriformes, Loricariidae) with emphasis on physical mapping of 18S and 5S rDNA sites

“…We found this situation in H. ancistroides and H. nigromaculatus, species that are widespread in Brazilian basins. All populations of H. ancistroides and H. nigromaculatus that have been studied showed 2n = 68 chromosomes (Artoni and Bertollo, 1996;Alves et al, 2006;Rubert et al, 2011) and 76 chromosomes (Rubert et al, 2008), respectively, with differences in karyotype formulae, heterochromatic pattern and NOR location. According to Bueno et al (2012), in addition to the centric fissions, pericentric and paracentric inversions also have an important role in karyotype diversification of Hypostomus, which could explain these population differences.…”