Localization and activity of rDNA genes in tiger beetles (Coleoptera: Cicindelidae).
ABSTRACT Siver staining of male meiotic nuclei of six species f the tiger beetle genus Cicindela (tribe Cicindelini), with multiple sex chromosomes, reveals the presence of active nucleolar organizing regions (NORs) in the sex vesicle. In one species, Cicindela melancholica, fluorescence in situ hybridization b(FISH) with a ribosomal probbe showed that rDNA genes are in one of the three X chromosomes and in the Y chromosome. Silver staining and FISH show that the related species Cicindela paludosa with a male XO system. has NORs located in one pair of autosomes. In Megacephala euphratica (tribe Megacephalini) these techniques indicate that NORs are located in three autosomal pairs but not in the single X chromosomes of males. In all these species the nucleolus can be seen from the onset of meiosis to the end of the diffuse stage; it disappears from diplotene to the end of meiosis and appears again during the spermatid stage. From these results it is concluded that: (i) the nucleolus does not seem to play a major role in the pairing and association of the multiple sex chromosomes during first meiotic prophase and metaphase; (ii) the occurrence of NORs in the heterosomes of species having multiple sex chromosomes is thought to be an ancestral condition for the genus Cicindela; and (iii) changes of location of NORs from heterosomes to the autosomes have occurred within species of this genus, at least in species showing extensive karyotypic repatterning.
Full-textDOI: · Available from: Eduard Petitpierre, May 05, 2015
SourceAvailable from: Alejandro López-López[Show abstract] [Hide abstract]
ABSTRACT: Meiotic behavior based on observations of the first and second divisions was studied in males of four taxa of the Australian tiger beetle genus Pseudotetracha of the tribe Megacephalini (Coleoptera). Pseudotetracha blackburni clade 1 shows 10 pairs of autosomes plus a trivalent that is hypothesized to be the result of either a translocation or a fusion in which the original heterosomes (very likely XY) and an autosomal pair are involved, giving rise to a recently established neo-X1X2Y sex chromosome system of chiasmatic nature. The origin of this karyotype has been determined to have taken place 2.30–3.72 million years in the past using a molecular clock based on the 16S rRNA substitution rate. Pseudotetracha blackburni clade 2 shows a meioformula of the type n = 11 + XY, the same as that found in the related taxon P. australis. Previous data for P. whelani, with 12 pairs of autosomes and an XY sex chromosome system, are confirmed in this survey. The multiple chiasmatic sex chromosome system of P. blackburni clade 1 is considered to be of recent origin and with an evolutionarily short-life confined to this species, where close relatives exhibit simple genetic systems, in contrast to the long evolutionary life of the multiple achiasmatic sex chromosome system broadly found in the tribes Cicindelini and Collyrini. The implications of this chromosomal rearrangement in terms of recombination and speciation are discussed. The results of this work, together with the available cytogenetic data for other Megacephalini species, are interpreted in the light of recent molecular phylogenies of the tribe, showing evidence of a possible process of karyotypic orthoselection with recurrent cycles of incorporation of autosomes to the heterosome pair and subsequent loss of the Y chromosome in Tetracha and Pseudotetracha.Journal of Zoology 04/2013; 289(4). DOI:10.1111/jzo.12003 · 1.95 Impact Factor
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ABSTRACT: The order Coleoptera comprises species that are used as models in evolutionary studies, such as Alticinae, which features giant sex chromosomes. Thus, the aim of the present study was to investigate the differentiation and evolution of the sex chromosome in species of the Omophoita genus (Alticinae) using repetitive DNA (total C0t-1), C-banding and base-specific fluorochromes. Analyses using probes generated through C0t-1 reassociation kinetics showed markers distributed across all the chromosomes, especially the sex chromosomes. In conclusion, repetitive sequences are distributed across the sex chromosomes and autosomes, demonstrating that the heterochromatin of the species is largely composed of repetitive DNA. Cross-hybridisation among the species produced a very similar staining pattern for the probes. Thus, we conclude that the majority of the genome of the species of Omophoita is shared, showing the heterochromatin to be largely composed of repetitive DNA distributed along the sex chromosomes and autosomes.Italian Journal of Zoology 04/2014; 81(1). DOI:10.1080/11250003.2014.882995 · 0.87 Impact Factor