XVI International Botanical Congess

Genetic population differentiation is typically viewed as differentiation of population means. However, theories of evolution and speciation postulate that populations differentiate not only for population means, but also with respect to the effects of alleles. I examine the differentiation of allelic effects in a metapopulation. I define Alocal average effect@ to be the average effect of an allele in a deme measured as a deviation from the metapopulation mean. The differentiation for local average effects is a form of population differentiation that is distinct from differentiation of population means. When there is only additive gene action populations only differentiate for population means. If there is gene interaction then populations can also differentiate for the local average effects of alleles. Differentiation of local average effect has important evolutionary implications. It provides a model for the formation of Aadaptive gene complexes@ and a genetic mechanism for speciation.