Variability in rDNA loci in Iberian species of the genus Zabrus (Coleoptera : Carabidae) detected by fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) with a PCR-amplified 18S ribosoma l probe was used to map rDNA loci in 19 taxa of the ground beetle genus Zab rus (2n = 47-63) from the Iberian Peninsula. A quantitative and qualitative variation has been observed among related species, subspecies, populations , and even individuals. The number of rDNA-carrying chromosomes varies from 2 to 12, and the extent of the signal from small dots to entire arms. Chan ges altering the number of rDNA clusters seem to be uncoupled from the vari ation found in the chromosome number. Mechanisms that explain the numerical variation and spreading of rDNA clusters throughout the genome within the genus Zabrus are briefly discussed. No concordance between the pattern of r DNA sites and the phylogenetic relationships as based on morphological char acters has been found.