Cryptic genetic variation can make "irreducible complexity" a common mode of adaptation in sexual populations Journal Article

Author(s): Trotter, Meredith V; Weissman, Daniel B; Peterson, Grant I; Peck, Kayla M; Masel, Joanna
Article Title: Cryptic genetic variation can make "irreducible complexity" a common mode of adaptation in sexual populations
Affiliation IST Austria
Abstract: The existence of complex (multiple-step) genetic adaptations that are "irreducible" (i.e., all partial combinations are less fit than the original genotype) is one of the longest standing problems in evolutionary biology. In standard genetics parlance, these adaptations require the crossing of a wide adaptive valley of deleterious intermediate stages. Here, we demonstrate, using a simple model, that evolution can cross wide valleys to produce "irreducibly complex" adaptations by making use of previously cryptic mutations. When revealed by an evolutionary capacitor, previously cryptic mutants have higher initial frequencies than do new mutations, bringing them closer to a valley-crossing saddle in allele frequency space. Moreover, simple combinatorics implies an enormous number of candidate combinations exist within available cryptic genetic variation. We model the dynamics of crossing of a wide adaptive valley after a capacitance event using both numerical simulations and analytical approximations. Although individual valley crossing events become less likely as valleys widen, by taking the combinatorics of genotype space into account, we see that revealing cryptic variation can cause the frequent evolution of complex adaptations.
Keywords: Adaptive valley; Complex adaptation; Evolutionary capacitance; Moran model; Theoretical population genetics
Journal Title: Evolution
Volume: 68
Issue 12
ISSN: 1558-5646
Publisher: Wiley-Blackwell  
Date Published: 2014-12-01
Start Page: 3357
End Page: 3367
Sponsor: Funded by National Institutes of Health. Grant Numbers: R01GM076041, R01GM104040 ERC. Grant Number: 250152 Simons Foundation
DOI: 10.1111/evo.12517
Notes: KMP received support from the Undergraduate Biology Research Program at the University of Arizona. GIP thanks A. Lancaster for discussion.
Open access: yes (repository)