Evolutionary Convergence and Divergence In A Model Fitness Landscape



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Fitness landscapes are the invisible force responsible for directing the course of evolution. Here, we look at the pattern of substitution of the first two mutations fixed in two diverging populations at high and no epistasis in an adaptive fitness landscape. We used a two loci system with a fitness landscape generated randomly using an NK model. For the case of no epistasis, we used a K = 0, and for the case of high epistasis, K = 1. If the mutations are neutral, the probability that one substitution occurs in each lineage, the probability of two substitutions occur in a single lineage, and the probability of convergence are all equal. However, this is not the case if the mutations are adaptive. Our simulations show that convergence occurs in over half of all cases in both epistasis levels. For the remaining, one substitution occurring in each diverging lineage is more likely to occur than two substitutions occurring in a single lineage under both levels of epistasis. Despite having identical patterns of substitution, our data suggests discrepancies in the average fitness benefit of mutations at each substitution between the two epistasis levels; this will be the subject of further investigation.