Figure 2

Mean performance (on a 0 to 1 scale) as a function of the effective population size (\(N_e\)), the selection coefficient (s), and the size of linkage groups, for the case of a biallelic model with the mutation rate to the beneficial allele being \(10\times\) the reciprocal rate. All results denote the selection-drift-mutation equilibrium performance (as described in the main text, but equal to the mean frequency of \(+\) alleles for the case of single effects). (Upper left) Results are given for the situation in which all sites have equal mutational effects, for four values of the selection coefficient s (bundles of curves) and six linkage-block sizes [color coded as in the inset of the lower left panel]. The cartoons to the right denote arbitrary stretches of linked sites with different fractions of sites containing \(+\) alleles (solid balls), increasing as mean performance increases. As s declines by a factor x, the curves shift to the right in an essentially constant pattern, such that a specific level of performance requires an x-fold increase in \(N_e\). (Lower left) The latter point is made by plotting the points in the upper left panel against the product \(N_e s\), which leads to nearly perfectly overlapping curves. (Lower right) Results for the situation in which two types of linked sites are simultaneously selected upon: the numbers and selection coefficients associated with large-effect sites are given within the graph, whereas the small-effect sites are \(10\times\) more abundant but have \(10\times\) smaller selective effects, such the full performance of the system is equally distributed over the linked sets of large- and small-effect sites.