directional epistasis

Schenk MF, Szendro IG, Salverda MLM, Krug J & de Visser JAGM 2013 Patterns of epistasis between beneficial mutations in an antibiotic resistance gene. Mol Biol Evol 30:1779-1787.

• it has been suggested that epistasis is stronger among mutations in the same gene than among mutations in different genes
• confounding methodological variation across studies has prevented solid tests

• we found support for the notion that large-effect beneficial mutations interact more strongly than small-effect mutations
• the effect size of mutations may be an organizing principle for understanding patterns of epistasis
• two recently published landscapes involving beneficial mutations in different bacterial genes (Chou et al. 2011; Khan et al. 2011) show an overall pattern of diminishing returns similar to the pattern that we observe