EVOLUTIONARY RATES IN PARTIALLY SELF-FERTILIZING SPECIES

This article develops models of the rates of fixation of mutant genes in partially self-fertilizing populations, with particular emphasis on the effect of the level of dominance of a favorable mutation on its probability of fixation. It is shown that even a moderate rate of selfing greatly increases the probability of fixation of a favorable recessive mutation in a large population. If favorable recessive mutations are commoner than dominant ones, recessive alleles should frequently be fixed by selection in partially selfing populations, in contrast to what is found for autosomal loci in large random-mating populations. This expectation was tested by comparing the frequency of dominant versus recessive derived traits in cases of recent evolution in selfing populations and was found to be supported. The effect of the rate of self-fertilization on the rate of fixation of deleterious mutations was found to be minor. The mte of fixation of chromosomal rearrangements with large heterozygous fertility losses is nonlinearly related to the rate of selfing unless population size is very small. This may explain comparative data on the relation between breeding system and rate of karyotypic evolution in plants.