Chromosomal diversification in ribosomal DNA sites in Ancistrus Kner, 1854 (Loricariidae, Ancistrini) from three hydrographic basins of Mato Grosso, Brazil

Sandra Mariotto,Roberto Artoni,Marcelo Vicari,Orlando Moreira Filho,Liano Centofante

doi:10.3897/compcytogen.v5i4.1757

Abstract

Populations of seven Ancistrus species were analyzed from streams and rivers of three hydrographic Brazilian basins. All populations showed different diploid numbers (2n), fundamental numbers (FNs), and karyotypes. Some representatives of Loricariidae have 2n = 54 chromosomes, which is very likely an ancestral cytotaxonomic characteristic, but many other representatives show extensive karyotype diversification. In the Ancistrus species studied, extensive karyotypic differentiation, which is generally associated with chromosome number reduction and rearrangement of the ribosomal RNA gene (rDNA) sites, was verified. Chromosomal locations of 18S and 5S rDNA were jointly detected using fluorescence in situ hybridization (FISH). In all the Ancistrus species analyzed, 18S rDNA sites were detected only on one chromosome pair, though this differed among species. 5S rDNA was located on 1–3 chromosome pairs either separately or in synteny with 18S rDNA in four of the seven species/populations. Hence the karyotype differentiation in Ancistrus species could be associated with a morphological speciation process, suggesting that chromosome fusions, inversions, deletions, duplications, and heterochromatination could contribute to the karyotype evolution of these neotropical armored catfishes.

Highlights

In eukaryotes, 5S and 18S ribosomal genes are arranged into two distinct classes, namely the major rDNA family composed of 18S, 5.8S, and 28S genes and the minor family composed of 5S genes (Long and David 1980, Pendás et al 1994)
Comparison using fluorescence in situ hybridization (FISH) associated with classical chromosomal markers has become the preferred method for genome comparisons at the cytogenetic level because it allows complete chromosome probes of a species to be hybridized in situ with chromosomes of other species, thereby allowing the detection of homologous genomic regions (Vicari et al 2010; Bellafronte et al 2011; Machado et al 2011)
nucleolar organizing regions (NORs) were seen in a single chromosome pair in all the Ancistrus sp. analyzed using silver nitrate staining and FISH with 18S rDNA probe (Fig. 1)

Summary

Introduction

5S and 18S ribosomal genes (rDNA) are arranged into two distinct classes, namely the major rDNA family composed of 18S, 5.8S, and 28S genes and the minor family composed of 5S genes (Long and David 1980, Pendás et al 1994). Comparison using fluorescence in situ hybridization (FISH) associated with classical chromosomal markers has become the preferred method for genome comparisons at the cytogenetic level because it allows complete chromosome probes of a species to be hybridized in situ with chromosomes of other species, thereby allowing the detection of homologous genomic regions (Vicari et al 2010; Bellafronte et al 2011; Machado et al 2011). A few such studies were conducted in Pimelodidade and Pseudopimelodidae, where non-syntenic 5S and 18S ribosomal regions were observed (Carvalho and Dias 2007; Garcia and Moreira-Filho 2008; Marques et al 2008; Matoso et al 2011; Moraes Neto et al 2011; Silva et al 2011). In Loricariidae, chromosomes with syntenic 5S and 18S regions were observed in some groups like Neoplecostominae and the out group Trichomycteridae (Ziemniczak 2011)

Methods

Results

Conclusion