DRUSE

Lawrence Weider and colleagues wrote a review in 2005 covering ribosomal DNA variation. They discussed the interaction between rDNA and growth rate. They also highlighted the role of selection on rDNA variants in the microevolutionary process. They concluded that using biological stoichiometry to examine how evolutionary forces operate on rDNA variation can have a major effect on ecological interactions, via the ribosome biogenesis.

Here’s a portion of it (LV = length variant of the intergenic spacer IGS):

“Among the few animal studies that have utilized artificial selection on specific traits (e.g., growth rate, life-history traits) and examined concomitant changes in rDNA, the studies by Cluster et al. (1987) and Grimaldi & Di Nocera (1988) on D. melanogaster are noteworthy because they show a clear response of the rDNA to directional selection. Cluster et al. (1987) selected for fast and slow development times among lines of D. melanogaster and noted a significant shift in the frequency of IGS LVs in the two selection regimes. A greater proportion of the faster developing lines maintained longer LVs, whereas the slower developing lines maintained shorter LVs. Subsequent work by Grimaldi & Di Nocera (1988) showed that the rate of transcriptional production of pre-rRNA was directly proportional to the number of enhancers located in the IGS. These two studies provide support for the notion that genotypes composed of longer IGS LVs may benefit from higher rDNA transcriptional rates via more enhancer and promoter sites in the subrepeat region of the IGS and thus exhibit faster development (higher growth rates).”