Chromosome evolution in the genus Cicindela: physical mapping and activity of rDNA loci in the tiger beetle species Cicindela littoralis and C. flexuosa

Abstract

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.

Chromosome evolution in tiger beetles: Karyotypes and localization of 18S rDNA loci in Neotropical Megacephalini (Coleoptera, Cicindelidae)

“…The autosomal localization of these gene clusters as well as the higher number of copies resemble other data for basal groups, such as Amblycheila and Manticora (eight rDNA loci) and Omus and Megacephala (six rDNA loci) (Galián and Hudson, 1999;Galián et al, 2002). In M. sobrina and M. cruciata (with eight and five rDNA loci, respectively) the ribosomal clusters occupied a distal position as observed in other cicindelids (Galián et al, 1995;Galián and Hudson, 1999;Proença et al, 2002a;Proença and Galián, 2003). Also, the size of the fluorescent region varied in the different chromosomes, with one signal being much larger than the others, covering almost all the short arm of the chromosome in M. sobrina.…”

“…Differences at population level regarding the number and distribution of ribosomal genes have already been described for the Cicindela species C. littoralis and C. flexuosa (Proença and Galián, 2003). In our study, however, an interesting aspect about the localization of ribosomal clusters was the presence of odd numbers of autosomal copies (three in M. rutilans and five in M. cruciata) since the same number of rDNA clusters should be expected in both homologous chromosomes.…”

“…Additional information regarding the genomic structure of tiger beetles have been limited to the application of C-banding to a restrict number of species and to the in situ localization of the 18S-28S ribosomal gene clusters (rDNA) (Galián et al, 1995;Galián and Hudson, 1999;Galián et al, 2002;Proença et al, 2002aProença et al, , b, 2004Proença and Galián, 2003;Zacaro et al, 2004). The number and distribution of these highly repetitive and conserved rDNA clusters can be useful for the construction of physical maps for comparative genomics and phylogenetic and evolutionary studies.…”

“…One exception to this model is the description of only two autosomal clusters in Megacephala brasiliensis, attributable to the unusually small number of autosomal pairs (Proença et al, 2002b). Recently, the localization of rDNA clusters in Cicindela littoralis and Cicindela flexuosa revealed the presence of interpopulation polymorphisms regarding the number of chromosomes with ribosomal genes and their localization within the genome (Proença and Galián, 2003). However, while the Cicindelini have been more or less well-studied, other tribes remain for which data are scarce because only a reduced number of species, mainly from basal groups, have been cytogenetically analyzed.…”

Cytogenetic variability in three species of the genus Cicindela (s.l.) (Coleoptera, Cicindelidae): karyotypes and localization of 18S rDNA genes

“…558 Proença et al In our research, the localization of major rDNA sites by FISH revealed different patterns for C. argentata, C. aurulenta and C. suturalis, with ribosomal clusters located in the autosomes, the heterosomes or in both. Different patterns regarding the localization of rDNA genes have been described in other Cicindela species : two clusters located in one autosomal pair (C. flexuosa, C. paludosa and C. hispanica); two clusters located in one autosomal pair and one in an X chromosome (C. littoralis and C. maura); two clusters located in one autosomal pair and two in the heterosomes (XY) (C. deserticoloides and C. circumdata) and three clusters located in the heterosomes (XXY) (C. trisignata) (see Proença et al, 2000;Proença and Galián, 2003). In our study we found two new rDNA localization patterns, i.e.…”