INBREEDING DEPRESSION UNDER A COMPETITIVE REGIME IN MIMULUS-GUTTATUS - CONSEQUENCES FOR POTENTIAL MALE AND FEMALE FUNCTION

The effects of one generation of selfing and outcrossing on six life history characters were examined in the greenhouse for two populations of the mixed-mating species Mimulus guttatus. Inbreeding depression was not detected in the mass of seed produced by maternal plants, but selfing significantly reduced germination success by 13-20 per cent relative to outcross seeds. Seedlings produced by self-pollination were 26-31 per cent smaller than outcross progeny. Late life history stages were examined under varied competitive regimes in which each plant was grown with a neighbour of either an inbred or outbred individual. Progeny resulting from self-pollinations showed a 14-30 per cent reduction in ovule number per locule, and their pollen production per flower was reduced by 28-33 per cent. Adult above-ground biomass showed the greatest inbreeding depression, ranging from 24-50 per cent depending on the competitive conditions. Thus progeny resulting from selfing are smaller as adults and contribute significantly fewer potential gametes into the gene pool as pollen grains and ovules. The multiplicative effects of these characters is calculated. For all traits except ovule number, outcross progeny from parents of the same population did not differ significantly from outcross progeny produced by parents that came from populations separated by 10 km, suggesting relatively little differentiation between populations. The relative performance of self and outcross progeny in later life history stages was independent of the relative performance observed in earlier stages.