Cryptic genetic variation can make “irreducible complexity” a common mode of adaptation in sexual populations |
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Authors: | Meredith V Trotter Daniel B Weissman Grant I Peterson Kayla M Peck Joanna Masel |
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Institution: | 1. Department of Biology, Stanford University, , Stanford, California, 95306;2. Department of Ecology and Evolutionary Biology, University of Arizona, , Tucson, Arizona, 85721;3. Institute of Science and Technology Austria, , Klosterneuburg, Austria;4. Current Address: Department of Physics, University of California, , Berkeley, California, 94720;5. Current Address: Department of Biology, University of North Carolina at Chapel Hill, , Chapel Hill, North Carolina, 27599 |
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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. |
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Keywords: | Adaptive valley complex adaptation evolutionary capacitance Moran model theoretical population genetics |
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