EFFECTS OF DIFFERENT LEVELS OF INBREEDING ON FITNESS COMPONENTS IN MIMULUS GUTTATUS.

Recent theoretical work has shown that there can be selection favoring the maintenance of sexual reproduction and the evolution of increased recombination when deleterious mutations at different loci interact synergistically, such that the logarithm of fitness declines at a greater than linear rate with the number of harmful mutations per genome. The purpose of this experimental study was to determine whether synergism exists for genes affecting fitness components in two partially selfing populations of the monkey flower Mimulus guttatus. For each wild population, a large randomly mated base population was constructed and many independent lines, inbred to differing degrees, were extracted from this base population. Lines with expected inbreeding coefficients of 0, 0.25, 0.5, and 0.75 were raised simultaneously in the greenhouse and were scored for germination, flowering, flower production, and pollen viability. All fitness traits except germination success declined with increased inbreeding, but in spite of the substantial inbreeding depression found in this study, relatively little evidence of synergistic epistasis was found. The only trait that showed evidence of synergism was pollen viability. These results indicate that synergism is not strong for the fitness components measured in this study. The evidence for synergism from other published studies is also reviewed.