Supplementary material from "Mutation bias can shape adaptation in large asexual populations experiencing clonal interference"

The Extended Evolutionary Synthesis invokes a role for development in shaping adaptive evolution, which in population genetics terms corresponds to mutation-biased adaptation. Critics have claimed that clonal interference makes mutation-biased adaptation rare. We consider the behaviour of two simultaneously adapting traits, one with larger mutation rate <i>U</i>, the other with larger selection coefficient <i>s</i>, using asexual travelling wave models. We find that adaptation is dominated by whichever trait has the faster rate of adaptation <i>v</i> in isolation, with the other trait subject to evolutionary stalling. Reviewing empirical claims for mutation-biased adaptation, we find that not all occur in the ‘origin-fixation’ regime of population genetics where <i>v</i> is only twice as sensitive to <i>s</i> as to <i>U</i>. In some cases, differences in <i>U</i> are at least ten to twelve times larger than differences in <i>s</i>, as needed to cause mutation-biased adaptation even in the ‘multiple mutations’ regime. Surprisingly, when <i>U</i> > <i>s</i> in the ‘diffusive-mutation’ regime, the required sensitivity ratio is also only two, despite pervasive clonal interference. Given two traits with identical <i>v</i>, the benefit of having higher <i>s</i> is surprisingly small, occurring largely when one trait is at the boundary between the origin-fixation and multiple mutations regimes.