The dynamic karyotype and the complex genetic structure of the obligate parthenogen Clonopsis gallica (Insecta: Phasmatodea)

The stick insects of the genus Clonopsis embody bisexual, parthenogenetic and androgenetic taxa. Clonopsis gallica is an obligate parthenogen with a very wide geographic range, spreading eastwards from Morocco to Tunisia, and across Gibraltar to southern Europe. The body morphology and the egg parameters and pattern are very stable throughout the geographic range, while cytological investigations on follicular mitotic plates and oocyte maturation mechanisms as well as mtDNA findings neatly separated the Moroccan C. gallica collections from the remaining African and European samples, thus revealing a complex phylogenetic scenario. Here we investigated, by two-colour fluorescence in situ hybridization (FISH) of 28S ribosomal and telomeric (TTAGG)n sequences, European C. gallica specimens from three allopatric Italian sites, namely Sicily, Sardinia and Tuscany. We confirmed the variability of mitotic chromosome number and revealed a shared occurrence of colocalized, highly-amplified ribosomal genes and (TTAGG)n interstitial telomeric sequences (ITSs). The labelled sites were constant within the same specimen, but variable in number and chromosome location among specimens, even those coming from the same collecting site. Moreover, the telomeric signals also labelled the centromeric/pericentromeric regions of a few chromosomes, thus showing the presence of another ITS class, generally considered to be the trace of chromosome rearrangements. The finding of different classes of ITSs located on several chromosomes of the complement makes the C. gallica karyotype highly dynamic; its diffuse chromosome repatterning well accounts for the differences between the Moroccan and non-Moroccan populations.