Negative Epistasis Between Beneficial Mutations in an Evolving Bacterial Population

Abstract

Epistatic interactions between mutations play a prominent role in evolutionary theories. Many studies have found that epistasis is widespread, but they have rarely considered beneficial mutations. We analyzed the effects of epistasis on fitness for the first five mutations to fix in an experimental population of Escherichia coli. Epistasis depended on the effects of the combined mutations--the larger the expected benefit, the more negative the epistatic effect. Epistasis thus tended to produce diminishing returns with genotype fitness, although interactions involving one particular mutation had the opposite effect. These data support models in which negative epistasis contributes to declining rates of adaptation over time. Sign epistasis was rare in this genome-wide study, in contrast to its prevalence in an earlier study of mutations in a single gene.

Quantifying natural seasonal variation in mutation parameters with mutation accumulation lines

“…In this case, the assayed population may be far from its optimum in the new environment, increasing the likelihood a mutation will be beneficial, as has been observed with experimental studies of microorganisms (Burch & Chao, 1999; Khan, Dinh, Schneider, Lenski, & Cooper, 2011; Kryazhimskiy, Rice, Jerison, & Desai, 2014; MacLean, Perron, & Gardner, 2010; Perfeito, Sousa, Bataillon, & Gordo, 2014) and in one field study with A. thaliana (Stearns & Fenster, 2016). It is also possible that there was within‐plant selection during the propagation of the mutation accumulation lines (Otto & Orive, 1995).…”

Genetic background affects epistatic interactions between two beneficial mutations

“…For example, several studies have examined specific examples of epistasis causing evolutionary contingency [12,13]. Other studies have demonstrated a trend for beneficial mutations to interact antagonistically, causing the rate of adaptation to slow as beneficial mutations accumulate [8,9,15], a relationship predicted by theory [16].…”

“…This dependence, known as epistasis, is important to many areas of developmental and evolutionary biology, including speciation [1][2][3][4], the maintenance of sex [5,6], adaptation [7][8][9], the evolution of ploidy [10] and evolutionary contingency [11 -14]. As the technology to identify and manipulate specific mutations becomes increasingly available, the influence of epistasis can be examined directly.…”

Évolution adaptative des bactéries

“…La question dès lors se pose des interactions entre ces mutations bénéfiques. Des résultats limités récents ont montré une action épistatique négative entre des mutations bénéfiques, avec décé-lération de l'adaptation [10,11]. Une telle action épistatique négative a été retrouvée dans les données du travail décrit ci-dessus avec des quasi-exclusions de mutations (la présence de mutation au codon 17 du gène rho est en complète répulsion avec la mutation au codon 966 de rpoB).…”