Genetic complexity of adapting populations.

A small number of point mutations rose to appreciable frequencies in each population with the exception of the allantoin-limited population, which contains ∼500 SNPs most of which have frequencies less than 10% (see Table S2 and Table S3). This population also contains a mutant MSH2 gene, suggesting the existence of a low frequency mutator phenotypes [73], [74]. Nitrogen concentrations were normalized between environments by adjusting the concentration of each compound according to its molecular composition.