Significance of differential allelic expression (DAE) in phenotypic plasticity and evolutionary potential of microbial eukaryotes

Background: Differential allelic expression (DAE) plays a key role in the regulation of many biological processes, and it may also play a role in adaptive evolution. Recently, environment-dependent DAE has been observed in species of marine phytoplankton, and most remarkably, alleles that showed the highest level of DAE also showed the fastest rate of evolution.
Methods: To better understand the role of DAE in adaptive evolution and phenotypic plasticity, we developed a 2-D cellular automata model “DAEsy-World” that builds on the classical Daisyworld model.
Results: Simulations show that DAE delineates the evolution of alternative alleles of a gene, enabling the two alleles to adapt to different environmental conditions and sub-functionalize. With DAE, the build-up of genetic polymorphisms within genes is driven by positive selection rather than strict neutral evolution, and this can enhance phenotypic plasticity. Moreover, in sexually reproducing organisms, DAE also increased the standing genetic variation, augmenting a species' adaptive evolutionary potential and ability to respond to fluctuating and/or changing conditions (cf. genetic assimilation). We furthermore show that DAE is likely to evolve in fluctuating environmental conditions.
Conclusions: DAE increases the adaptive evolutionary potential of both sexual and asexually reproducing organisms, and it may affect the pattern of nucleotide substitutions of genes.