mutation landscape
Franke J, Klözer A, de Visser JAGM & Krug J 2011 Evolutionary accessibility of mutational pathways. PLoS Comput Biol 7:e1002134.
- does epistasis make the global fitness optimum selectively inaccessible?
- this question has a long history in evolutionary theory
- two contradictory intuitions can be discerned in the still ongoing debate
- one viewpoint generally attributed to Fisher [19] emphasizes the proliferation of mutational pathways in high dimensional genotype spaces
- because of the sheer number of possible paths, accessibility will remain high
- the second line of argument originally formulated by Wright [20], and more recently promoted by Kauffman [21] and others, focuses instead on the proliferation of local fitness maxima
- which present obstacles to adaptation and reduce accessibility with increasing genotypic dimensionality
- both views are valid at a qualitative level
- Fisher's scenario prevails on the basis of a specific, quantitative definition of accessibility, since the number of accessible pathways grows much faster with landscape dimensionality than the inaccessibility per pathway as long as the fitness landscape is not completely uncorrelated
- we assume a 'strong-selection/weak mutation' (SSWM) regime
- mutations are selected one by one and prohibits the populations from crossing valleys of fitness
- in natural populations of sufficient size, a number of double mutants is present at all times
- the crossing of fitness valleys can be relatively facile
- the SSWM assumption may therefore seem overly restrictive
- even under these conditions, the landscapes considered are typically very accessible
