  Mutational robustness quantifies the effect of random mutations on fitness.
When mutational robustness is high, most mutations do not change fitness or
have only a minor effect on it. From the point of view of fitness landscapes,
robust genotypes form neutral networks of almost equal fitness. Using
deterministic population models it has been shown that selection favors
genotypes inside such networks, which results in increased mutational
robustness. Here we demonstrate that this effect is massively enhanced by
recombination. Our results are based on a detailed analysis of mesa-shaped
fitness landscapes, where we derive precise expressions for the dependence of
the robustness on the landscape parameters for recombining and non-recombining
populations. In addition, we carry out numerical simulations on different types
of random holey landscapes as well as on an empirical fitness landscape. We
show that the mutational robustness of a genotype generally correlates with its
recombination weight, a new measure that quantifies the likelihood for the
genotype to arise from recombination. We argue that the favorable effect of
recombination on mutational robustness is a highly universal feature that may
have played an important role in the emergence and maintenance of mechanisms of
genetic exchange.
