Chromosomal location of 18S and 5S rDNA sites in Triportheus fish species (Characiformes, Characidae)

Débora Diniz,Alejandro Laudicina,Luiz Antonio Carlos Bertollo

doi:10.1590/s1415-47572009005000017

Débora Diniz, Alejandro Laudicina + Show 1 more

Open Access

https://doi.org/10.1590/s1415-47572009005000017

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Abstract

The location of 18S and 5S rDNA sites was determined in eight species and populations of the fish genus Triportheus by using fluorescent in situ hybridization (FISH). The males and females of all species had 2n = 52 chromosomes and a ZZ/ZW sex chromosome system. A single 18S rDNA site that was roughly equivalent to an Ag-NOR was detected on the short arms of a submetacentric pair in nearly all species, and up to two additional sites were also observed in some species. In addition, another 18S rDNA cluster was identified in a distal region on the long arms of the W chromosome; this finding corroborated previous evidence that this cluster would be a shared feature amongst Triportheus species. In T. angulatus, a heterozygotic paracentric inversion involving the short arms of one homolog of a metacentric pair was associated with NORs. The 5S rDNA sites were located on the short arms of a single submetacentric chromosomal pair, close to the centromeres, except in T. auritus, which had up to ten 5S rDNA sites. The 18S and 5S rDNA sites were co-localized and adjacent on the short arms of a chromosomal pair in two populations of T. nematurus. Although all Triportheus species have a similar karyotypic macrostructure, the results of this work show that in some species ribosomal genes may serve as species-specific markers when used in conjunction with other putatively synapomorphic features.

Highlights

The advent of fluorescent in situ hybridization (FISH) has made it possible to map specific DNA sequences in plants and animals
We examined the chromosomal locations of the 18S and 5S rDNA sites of several Triportheus species and populations, and assessed the usefulness of these sites as possible chromosomal markers within and among species
In T. angulatus, in which only females were studied, hybridization signals were observed on five chromosomes: in two cases they were located on the short arms of a metacentric pair, in another two cases they were located on the long arms of a meta-submetacentric pair and in one case the site was located at a distal position on the long arm of the W chromosome (Figure 2f)

Summary

Introduction

The advent of fluorescent in situ hybridization (FISH) has made it possible to map specific DNA sequences in plants and animals. Two important features have contributed to the widespread use of FISH with ribosomal DNA probes, namely, the organization of rRNA genes that consist of multiple repeats and the presence of highly conserved nucleotide sequences that are very similar among eukaryotes in general. Fish of the genus Triportheus, popularly known as “sardinhas de água doce”, “sardela” or “sardinha facão”, have a widespread distribution throughout South America, ranging from Colombia to Uruguay. These fish, which may reach 20-24 cm in length, are an important source of food in certain regions of Brazil such as the Amazon. In a recent review of the genus, Malabarba (2004) considered 16 valid species, with some of the names being regarded as syn-

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