Adaptation of asexual populations in correlated environments

We introduce two computational models of subdivided populations of asexual organisms which present variability in selection pressure. In both models one can handle the level of environmental correlation among the subpopulations (demes), which is dependent on the length of the shortest path between the demes. This work mainly addresses how environmental heterogeneity can affect the rate at beneficial mutations fixes in a structured population, and the conditions under which clonal interference becomes significant. Although the fixation probability of beneficial mutations is roughly the same as in a panmitic population and so does not depend on the level of correlation among the demes, the simulation results show that fixation rates may be strongly influenced by environmental variability. Based on our simulations we conclude that an increased variability in selection leads to a smaller fixation rate. The effect of environmental heterogeneity on the adaptive process is enhanced as the flow of organisms between subpopulations is reduced. In extreme scenarios, the fixation rate decreases as the rate of beneficial mutations rises. (C) 2010 Elsevier B.V. All rights reserved.