Evolution of satellite DNAs from the genus Palorus--experimental evidence for the "library" hypothesis

Satellite DNA profiles have been characterized in the congeneric speciesPalorus ratzeburgii, Palorus subdepressus, Palorus genalis, and Palorusficicola (Coleoptera, Insecta), each of which contains a single, A + T-richsatellite DNA comprising a considerable portion of the genome (20%-40%).These satellites exhibit insignificant mutual sequence similarity. UsingPCR assay, it has been shown that all four sequences are present in each ofthe tested Palorus species: one of them is amplified into a high copynumber or a major satellite, while the three others are in the form oflow-copy-number repeats estimated to make up approximately 0.05% of thegenome. Each of the four satellites is interspecifically high conservedconcerning the sequence, monomer length, and tandem repeat organization.Major, as well as low- copy-number, satellites are colocalized in theregions of pericentromeric heterochromatin on all chromosomes of thecomplement. The low-copy-number satellites are dispersed between the largearrays of the major satellite over the whole heterochromatic block. Ourresults explain satellite DNA evolution, confirming the hypothesis thatrelated species share a "library" of conserved satellite sequences, some ofwhich could be amplified into a major satellite. Due to the evolutionarydynamics of satellite DNAs, the content of the "library" is variable; theelimination of some sequences parallels the creation of the new ones.Quantitative changes in satellite DNAs, induced by occasional amplificationof satellite repeat from the "library", could possibly occur in the courseof the speciation process, thus forming a species-specific profile ofsatellite DNAs.