- The ribosomal cistron (rDNA cistron) is a tandemly repeated region in the genome that encodes for the necessary subunits to form ribosomes, complex molecules responsible for the assembly of amino acids into proteins. They are found within all cellular organisms, and evolve at relatively constant rates, making them ideal for comparative analysis. A significant difference in rDNA copy number was observed in a recent Illumina sequencing analysis of a group of Bembidion ground beetles known as the breve group. Graph-based cluster analyses of repetitive sequences conducted using the program RepeatExplorer showed strong support for an increase in rDNA copy number in Bembidion lividulum, and matched expected results for four other breve group species as well. In addition, patterns of variation in genome proportions and transposable element abundance were consistent with phylogenetic and geographic relationships in B. lividulum and B. laxatum, suggesting that repetitive content may be in an important factor for differences in genomic architecture within and between species.