Background: Genetic systems involving multiple X chromosomes have arisen repeatedly in sexually reproducing animals. Tiger beetles (Cicindelidae) exhibit a phylogenetically ancient multiple-X system typically consisting of 2-4 X chromosomes and a single Y. Because recombination rates are suppressed in sex chromosomes, changes in their numbers and movement of genes between sex chromosomes and autosomes, could have important consequences for gene evolution and rates of speciation induced by these rearrangements. However, it remains unclear how frequent these rearrangements are and which genes are affected.
Cicindela littoralis and Cicindela flexuosa were analysed at population level to determine the localization and activity of ribosomal genes. Fluorescence in situ hybridization (FISH), using a PCR-amplified 18S rDNA fragment as a probe, revealed the presence of polymorphism regarding the number of chromosomes with ribosomal genes as well as their localization within the genome. Nine populations of C. littoralis showed a consistent pattern of two loci located in an autosomal pair (active during spermatogenesis as shown by silver staining) and one locus located in one of the multiple X chromosomes (silent during spermatogenesis), whereas individuals from the population of Punta Entinas showed only signals in the autosomal pair, lacking the heterosomal locus. In C. flexuosa, two patterns were also observed. Nine populations showed two loci in an autosomal pair whereas individuals from the population of San Pedro del Pinatar showed the two loci located in the heterosomes (one of the multiple Xs and in the Y). The hypothesis that these two different populations may reflect a status of well-differentiated phylogenetic entities is not supported for C. littoralis after the phylogenetic analysis of a fragment of the cytochrome oxidase I gene.
-Karyological investigations were carried out on five species of tiger beetles from the Afrotropical Region belonging to the tribes Megacephalini and Cicindelini. The species have distinct karyotypes either in the number of autosomes and heterosomes or in size and shape of the chromosomes: Megacephala megacephala and Prothyma lepneurii have 2n = 24+X,X 2 Y/ 24+X 1 X 1 X 2 X 2 , Euryarthron festwum has 2n= 22+X ] X 2 Y/22+X 1 X 1 X 2 X 2 , Ropaloteres feisthameli has 2n = 20+X 1 X 2 X,X 4 Y/20+XiX 1 X 2 X 2 X 3 X 3 X 4 X 4 and Hipparid-ium intenuptum has 2« = 20+X ] X 2 X 3 Y/20+XjX 1 X 2 X2X3X 3 . The existence of 12 pairs of autosomes in tribe Cicindelini is reported for the first time, being found in the genus Prothyma, the most ancient genus of this tribe. This supports the hypothesis that the chromosomal evolution in the Cicindelidae involved a reduction in number of chromosomes in the derived groups since the same number of autosomes or even more were found to occur in the most primitive tribes Collyrini and Megacephalini. All species have multiple sex chromosomes, apparently a characteristic of this family. Ropaloteres feisthameli has a sex chromosome system with four X chromosomes, only described for Cicindela maroccana pseudomar-occana and Cylindera trisignata.
In this work, the first cytogenetic data on Neotropical Collyrinae is provided, by way of their karyotypes, C-banding and ribosomal genes (rDNA) localization using fluorescence in situ hybridization (FISH). The two species analysed, Ctenostoma (Procephalus) ornatum ornatum (male) and Ctenostoma (Euctenostoma) rugosum (female) showed, respectively, a diploid number of 17 and 18 chromosomes. C. ornatum ornatum has a multiple sex chromosome system (n = 7 + X1X2Y), and mitotic and meiotic metaphase cells showed rDNA gene labelling in the smallest autosomal pair. In this species, no C-bands were obtained, while C. rugosum seems to exhibit centromeric and/or interstitial C-bands in almost all chromosomes. The observation of a multiple sex chromosome system in Ctenostomini ensured the appearance of this characteristic in the hypothetical ancestral of Collyrinae and Cicindelini. The subfamily Collyrinae is not uniform in what concerns diploid chromosome number and rDNA gene localization, because C. ornatum ornatum possesses a lower chromosome number and autosomal rDNA genes when compared with the other Collyrinae species studied (Neocollyris spp.). Independent events leading to the reduction in chromosome number might have taken place during the split of the Collyrinae into the tribes Ctenostomini and Collyrini.
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