Ribosomal DNA (rDNA) spacer polymorphism in mole rats

Genetic differentiation of ribosomal DNA (rDNA) nontranscribed-spacer (NTS) polymorphism was analyzed in 50 individuals from 13 populations among the four chromosomal species (2n = 52, 2n = 54, 2n = 58, and 2n = 60) of subterranean mole rats of the Spalax ehrenbergi complex in Israel. Southern blot analysis with a mouse rDNA probe and two restriction enzymes, EcoRI and BamHI, revealed various sizes of major restriction fragments. The assumption that this variation is due to length polymorphism of NTS DNA was supported by the construction of restriction-site maps. On the basis of the EcoRI and BamHi fragment lengths, we could characterize the major types of NTS rDNA repeating units in each individual. Each member of the central population in the four chromosomal groups of mole rats has a characteristic combination of the NTS types, suggesting that the karyotype groups were genetically diverged. Some near-hybrid-zone populations reflect similarities with the rDNA spectra of a neighbor chromosomal group. This might have resulted from gene flow across the hybrid zones.