Abstract
Two populations of Astyanax altiparanae (Garutti & Britski, 2000) of the Água dos Patos stream/SP and lake Igapó/PR were analyzed. All individuals showed 2n = 50, however, different karyotypic formulae were observed. The population of the Água dos Patos stream showed 8m +24sm+6st+12a (NF=88) and the population of lake Igapó, 8m+28sm+4st+10a (NF=90). Nucleolus organizing regions (AgNORs) were observed in the terminal position on the short and long arm of different chromosomes of both populations, showing a variation from 3 to 4 chromosomes. Fluorescent in situ hybridization (FISH) using 18S rDNA probes revealed only one pair of chromosomes with fluorescent signals in the terminal site on the short arm in the Igapó lake population, while the population of Água dos Patos stream showed 4 fluorescence terminal signals, characterizing a system of simple and multiple NORs, respectively. 5S rDNA fluorescent signals were detected in the interstitial position of a pair of chromosomes in the two studied populations. Some AgNOR sites revealed to be GC-rich when stained with Chromomycin A3 (CMA3), however, AT positive regions were not observed. The data obtained show that, despite the conservation of the diploid number and location of 5S DNAr, differences in both the distribution of 18S rDNA and karyotypic formula among the populations were found, thus corroborating the existing data on chromosome variability in Astyanax altiparanae that can be significant for cytotaxonomy in this group.
Highlights
Astyanax Baird et Girard, 1854, the most common and diversified genus within the family Characidae, has a wide distribution in the Neotropical Region
In view of the great chromosome variation observed by other authors in the genus Astyanax, the objective of the present work was to characterize the karyotypes of two populations of Astyanax altiparanae, with emphasis on the location of 18S and 5S DNAr sites, and compare them with data contained in the literature, in an endeavor toward a better understanding of chromosome evolution within this fish group
The population of the Água dos Patos stream showes 2 to 4 AgNORs on the short arm, in two equal medium-sized subtelocentric chromosomes, one of which revealed size heteromorphism observed in all metaphases (Fig. 3a)
Summary
Astyanax Baird et Girard, 1854, the most common and diversified genus within the family Characidae, has a wide distribution in the Neotropical Region. In Astyanax altiparanae (Garutti et Britski, 2000) from the upper Parana river basin, previously identified as Astyanax bimaculatus (Linnaeus, 1758), all cytogenetic studies accomplished so far reported the occurrence of 2n = 50, with differences in the karyotypic formula among the analyzed populations (Ferreira Neto et al 2009), which can be explained by the occurrence of chromosome rearrangements, such as pericentric inversions (Domingues et al 2007). Besides the differences in karyotypic formula, the nucleolus organizer regions in this species vary in relation to number and position, as observed by Fernandes and Martins-Santos (2006a), Domingues et al (2007), Ferreira Neto et al (2009). The same authors found evidence for conservation in relation to the location and number of fluorescent signals of 5S rDNA sites located in the interstitial region of one chromosome pair
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