GENE INTERACTION AFFECTS THE ADDITIVE GENETIC VARIANCE IN SUBDIVIDED POPULATIONS WITH MIGRATION AND EXTINCTION

We investigated the effect of nonadditive genetic variance on the amou nt of additive genetic variance within local populations in an infinit e-allele, infinite-island model with migration, extinction, and recolo nization, using two-locus descent measures. For an island model with e xtinction, one- and two-locus descent measures are expressed in a matr ix form that allows equilibrium solutions to be calculated similar to previous work on Wright's F-statistics. In a subdivided population, th e additive genetic variation within a local deme depends on the domina nce and epistatic genetic variation in the species. Moreover, to a goo d approximation, the amount of additive variance within a deme is a si mple function of F-st, which is twice the demic fraction of genic vari ance. At equilibrium, it is equal to (1 - F-st) V-A plus 4 F-st (1 - F -st) V-AxA, where V-A and V-AxA are the additive and additive x additi ve epistatic variances at the level of the species, respectively, plus a contribution from the dominance variance and other terms including dominance. Paradoxically, with nonadditive genetic effects, drift on a verage increases the amount of additive genetic variance within popula tions, whereas migration decreases the equilibrium amount. In the pres ence of nonadditive genetic effects, measurements of additive genetic variance in natural populations must be taken at the proper spatial sc ale with respect to natural selection, or they will provide an inaccur ate description of evolutionary potential both within local population s and within the species as a whole.