EPISTASIS AS A SOURCE OF INCREASED ADDITIVE GENETIC VARIANCE AT POPULATION BOTTLENECKS

The role of epistasis in evolution and speciation has remained controv ersial. We use a new parameterization of physiological epistasis to ex amine the effects of epistasis on levels of additive genetic Variance during a population bottleneck. We found that all forms of epistasis i ncrease average additive generic variance in finite populations derive d from initial populations with intermediate allele frequencies. Avera ge additive variance continues to increase over many generations, espe cially Lit larger population sizes (N = 32 to 64). Additive-by-additiv e epistasis is the most potent source of additive genetic variance in this situation, whereas dominance-by-dominance epistasis contributes s maller amounts of additive genetic variance. With additive-by-dominanc e epistasis, additive genetic variance decreases at a relatively high rate immediately after a population bottleneck, rebounding to higher l evels after several generations. Empirical examples of epistasis for m urine adult body weight based on measured genotypes are provided illus trating the varying effects of epistasis on additive genetic variance during population bottlenecks.