XVI International Botanical Congess

The balance between mutation and selection of partially recessive, deleterious mutations is a major source of inbreeding depression. The theoretical relation between this genetic basis and mating system is thoroughly investigated for annuals but not perennials. In perennials, weaker mutation results from reduced rates of mitotic relative to meiotic mutation. Consequently, perennials exhibit weaker inbreeding depression than annuals and are more susceptible to the evolution of selfing. On the other hand, selection over extended perennial life histories acts as a sieve on the dominance coefficient of mutations, so that mutations in perennials are more recessive than in annuals. Perennials then exhibit substantial inbreeding depression. These results indicate the complexities arising from realistic genetic models of perennial inbreeding depression.