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

Abstract

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 fl uctuating and/or changing conditions ( cf . genetic assimilation). We furthermore show that DAE is likely to evolve in fl uctuating 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. Author summary: In diploid organisms, the differential expression of the two alleles of a gene gives individuals more opportunities to adapt to fl uctuating environmental conditions, which is particularly bene fi cial for clonally reproducing species.