Patterns of rDNA chromosomal localization in Palearctic Cephalota and Cylindera (Coleoptera: Carabidae: Cicindelini) with different numbers of X-chromosomes

Jose Galian,Sonia J R Proença,Jose Serrano,Artur R.M Serrano

doi:10.3897/compcytogen.v5i1.962

Jose Galian, Sonia J R Proença + Show 2 more

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https://doi.org/10.3897/compcytogen.v5i1.962

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Journal: Comparative cytogenetics	Publication Date: May 5, 2011
Citations: 2	License type: CC BY 3.0

Affiliation: University of Lisbon

Abstract

The ribosomal clusters of six Paleartic taxa belonging to the tiger beetle genera Cephalota Dokhtourow, 1883and Cylindera Westwood, 1831, with multiple sex chromosomes (XXY, XXXY and XXXXY) have been localised on mitotic and meiotic cells by fluorescence in situ hybridization (FISH), using a PCR-amplified 18S rDNA fragment as a probe. Four patterns of rDNA localization in these tiger beetles were found: 1. Two clusters located in one autosomal pair; 2. Two clusters located in one autosomal pair and one in an X chromosome; 3. Three clusters located in three heterosomes (XXY); 4. Two clusters located in one autosomal pair and two in the heterosomes (one of the Xs and the Y). These results illustrate that ribosomal cistrons have changed their number and localization during the evolution of these genera, showing a dynamic rather than a conservative pattern. These changes in rDNA localization are uncoupled with changes in the number of autosomes and/or heterosomes. A mechanism that involves transposable elements that carry ribosomal cistrons appears to be the most plausible explanation for these dynamics that involve jumping from one location in the genome to another, in some cases leaving copies in the original location.

Highlights

Often closely related species differ in their karyotypes, both in terms of changes in chromosome number and morphology and/or localization of genes in chromosomes
Males and females were analysed in all species, in Cephalota deserticoloides, C. circumdata and Cylindera paludosa, only males provided interpretable plates
The karyotypes of Cephalota hispanica, C. maura and Cylindera trisignata are represented in Figure 1 to illustrate the three types of multiple sex chromosome systems

Summary

Introduction

Often closely related species differ in their karyotypes, both in terms of changes in chromosome number and morphology and/or localization of genes in chromosomes. Whether these changes have played a significant role as isolation mechanisms in speciation (White 1978; King 1993), or have been an accompanying consequence of this isolation (Futuyma and Mayer 1980; Coyne and Orr 2004) has generated some debate among cytogeneticists. Within the more recent tribe Cicindelini the generalized karyotype is made up of nine to eleven autosomal pairs of decreasing size (Galián et al 1990), plus a sex chromosome mechanism of the XnY type, where n varies between 2 and 4 that forms a non-chiasmatic multivalent connected by telomeric proteins during meiosis (Giers 1977). Single systems (XY/XX and X0/XX) have been considered as an ancestral state in the morphologically more primitive lineages, namely the tribes Megacephalini (Serrano et al 1986; Galián and Hudson 1999; Proença et al 2002b), Mantichorini and Omini (Galián et al 2002)

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