Mutation bias can shape adaptation in large asexual populations experiencing clonal interference

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 287; no. 1937; p. 20201503
• Main Authors: Gomez, Kevin, Bertram, Jason, Masel, Joanna
• Format: Journal Article
• Language: English
• Published: England The Royal Society 28.10.2020
• Subjects: Adaptation, Physiological - genetics; Evolution; Genetics, Population; Mutation; Mutation Rate; Reproduction, Asexual - genetics; developmental bias; mutation-driven adaptation; modern synthesis; standard evolutionary theory; parallel adaptation; elasticity
• DOI: 10.1098/rspb.2020.1503
• ISSN: 0962-8452; 1471-2954

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 U , the other with larger selection coefficient s , using asexual travelling wave models. We find that adaptation is dominated by whichever trait has the faster rate of adaptation v 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 v is only twice as sensitive to s as to U . In some cases, differences in U are at least ten to twelve times larger than differences in s , as needed to cause mutation-biased adaptation even in the ‘multiple mutations’ regime. Surprisingly, when U > s in the ‘diffusive-mutation’ regime, the required sensitivity ratio is also only two, despite pervasive clonal interference. Given two traits with identical v , the benefit of having higher s is surprisingly small, occurring largely when one trait is at the boundary between the origin-fixation and multiple mutations regimes.