The library model for satellite DNA evolution: a case study with the rodents of the genus Ctenomys (Octodontidae) from the Iberá marsh, Argentina.

On the basement of the library model of satellite DNA evolution is the differential amplification of subfamilies through lineages diversification. However, this idea has rarely been explored from an experimental point of view. In the present work, we analyzed copy number and sequence variability of RPCS (repetitive PvuII Ctenomys sequence), the major satellite DNA present in the genomes of the rodents of the genus Ctenomys, in a closely related group of species and forms inhabiting the Iberá marsh in Argentina. We studied the dependence of these two parameters at the intrapopulation level because in the case of interbreeding genomes, differences in RPCS copy number are due to recent amplification/contraction events. We found an inverse relationship among RPCS copy number and sequence variability: amplifications lead to a decrease in sequence variability, by means of biased homogenization of the overall satellite DNA, prevailing few variants. On the contrary, the contraction events that involve tandems of homogeneous monomers contribute-by default-minor variants to become "evident", which otherwise were undetectable. On the other hand, all the RPCS sequence variants are totally or partially shared by all the studied populations. As a whole, these results are comprehensible if these RPCS variants preexisted in the common ancestor of this Ctenomys group.