Chromosome Mapping of 18S Ribosomal RNA Genes in Eleven Hypostomus Species (Siluriformes, Loricariidae): Diversity Analysis of the Sites

Abstract

We investigated the chromosomal distribution of 18S ribosomal DNA (rDNA) in different populations of 11 species of Hypostomus collected in important Brazilian basins, namely South Atlantic, Upper Paraná, and Paraguay applying the fluorescence in situ hybridization (FISH). Hypostomus cochliodon, Hypostomus commersoni, Hypostomus hermanni, Hypostomus regani, Hypostomus albopunctatus, Hypostomus paulinus, Hypostomus aff. paulinus, Hypostomus iheringii, and Hypostomus mutucae presented multiple 18S rDNA sites while Hypostomus strigaticeps and Hypostomus nigromaculatus exhibited a single pair of chromosomes with 18S rDNA sites. The studied species presented variations in the number and position of these sites. The results accomplished were similar to those obtained by the analysis of AgNORs, revealing the same interspecific variability. Each species exhibited distinctive patterns of AgNOR and 18S rDNA distribution, which can be considered cytogenetic markers in each species of the genus and help improve the discussions on the phylogeny of the group.

Constitutive heterochromatin heteromorphism in the Neotropical armored catfish Hypostomus regani (Ihering, 1905) (Loricariidae, Hypostominae) from the Paraguay River basin (Mato Grosso do Sul, Brazil)

“…This is considered to be a derived trait in Locariids (Bueno et al 2013, 2014). The mapping of the 18S rDNA gene in other H.regani populations has demonstrated multiple sites, located in the terminal position, mostly on the short arms of the st/a chromosomes (Rubert et al 2016), which contrasts with the findings of the present study, given that the specimens of H.regani analyzed here presented single NORs, with active NOR and the 18S rDNA sites located in a terminal position on the short arms of submetacentric pair 10. Thus these chromosomes can be considered markers for the H.regani populations from Paraguay River basin.…”

“…The chromosomal heteromorphism detected in H.regani from Onça Stream, in the Taquari River basin, and investigated by chromosome painting provides an important model for the cytogenetic analysis for other species of the genus, in addition to other fish genera in which the role of the heterochromatin in differentiation and evolution of karyotypes need to be better understood. The divergence in karyotype formulas found among different populations of H.regani (Rubert et al 2016) suggests the existence of cryptic species within this taxon, and emphasizes the need of a thorough revision of the taxonomy of this group. While the taxonomic complexity of the genus Hypostomus is still far from being sorted out, cytogenetic analyses based on high resolution techniques, such as those applied in the present study, should help to reduce the taxonomic uncertainties in this genus.…”

“…Despite the uniform diploid number in this species, this comparison highlighted different karyotype formulas, including those of the present study, as well as differences in the position and amount of rDNA clusters (18S and 5S). This variability, summarized for Hypostomus by Rubert et al (2016), suggests a cryptic diversity in H.regani and the need for a taxonomic revision of this species.…”

“…The genus Hypostomus is cytogenetically highly diversified, with a wide range of diploid (2n=64–84) and fundamental (FN = 82–121) numbers as well as, inter- and intra-specific differences in the number and position of 18S and 5S rDNA clusters (Bueno et al 2014, Lorscheider et al 2015, Rubert et al 2016). In fish, the amount and position of the heterochromatic blocks have been related to the occurrence of chromosomal rearrangements or amplifications, especially during the origin and evolution of specific chromosomes, such as sex chromosomes and B chromosomes (Vicari et al 2010).…”

Studies in two allopatric populations of Hypostomus affinis (Steindachner, 1877): the role of mapping the ribosomal genes to understand the chromosome evolution of the group

“…These data, however, are rare for most fish, although some trends have been observed in smaller groups and have been examined in detail. In Hypostomus , through the efforts of different research groups, 18S gene localization data are available for approximately 30 species/populations (for review, see Rubert et al 2016). …”