Abstract
In this study, which is the first karyotype analysis of Hypostomus iheringii, nine specimens collected in Córrego da Lapa (tributary of the Passa-Cinco River) showed a diploid number of 80 chromosomes. Silver nitrate staining and fluorescence in situ hybridization (FISH) with an 18S rDNA probe revealed the presence of multiple nucleolus organizer regions (NORs) (chromosome pairs 13, 20, and 34). FISH with a 5S rDNA probe showed that this cistron was only present in chromosome pair 2. When the karyotypes of individual animals were compared, unique heterochromatic polymorphisms were detected on chromosome pairs 1 and 5. Specifically, specimens had heterochromatic blocks (h+h+) on both chromosomes, one chromosome with heterochromatic blocks (h+h-) or chromosomes that lacked heterochromatic blocks (h-h-). Considering that heteromorphic pattern is not correlated with variation in size, the process of heterochromatinization might act on the long arms of these chromosomes. In summary, all chromosomal markers indicate that the karyotype of Hypostomus iheringii is highly differentiated and that the heterochromatinization of chromosomal segments may have contributed to its karyotypic differentiation.
Highlights
All chromosomal markers indicate that the karyotype of H. iheringii is highly differentiated and that the heterochromatinization of chromosomal segments may have contributed to its karyotypic differentiation
fluorescence in situ hybridization (FISH) revealed that the 5S rDNA sites were located in the interstitial portion of the short arm of a metacentric chromosome (Fig. 3b)
In Hypostomus, the diploid number ranges from 54 chromosomes in Hypostomus plecostomus Linnaeus, 1758 (Muramoto et al 1968) to 84 chromosomes in Hypostomus sp. 2 (Cereali et al 2008)
Summary
Josiane Baccarin Traldi et al / Comparative Cytogenetics 6(2): 115–125 (2012). Armbruster (2004) considered the old subfamily Ancistrinae to be a synonym of Hypostominae, a group that currently consists of the tribes Corymbophanini, Rhinelepini, Hypostomini, Pterygoplichthini and Ancistrini. Hypostomus is the type genus of Hypostominae and has great morphological (Weber 2003) and cytogenetic (Bueno et al 2011) diversity. According to Weber (2003), the genus consists of a large number of species that exhibit a high level of morphological and color pattern variation, making systematic identification difficult. Ziemniczak et al (in press) concluded that the karyotypic differentiation of Hypostomini is correlated with the great diversification of form in this tribe and may have been important for genetic and reproductive isolation between species
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