Offspring fitness and parental effects as a function of inbreeding in Epilobium angustifolium (Onagraceae)

The fitness of plant offspring is determined not only by their nuclear genotype but also by non‐nuclear contributions and provisioning by parents (parental effects). Nuclear and parental effects on the production and germination of offspring were estimated for self‐, full‐sibling and outbred pollinations in a diallel crossing design involving eight plants of Epilobium angustifolium . Seed‐set and germination were significantly higher in offspring derived from outbred pollinations than from self‐pollinations. Full‐sib pollinations had intermediate seed‐set and germination but were not statistically different from self‐pollinations. The average nuclear contribution to offspring fitness was not significantly different among plants; however, variation in mean seed‐set and germination percentage among particular parent combinations, which was attributable to nuclear effects, was highly significant. Parental effects accounted for a significant portion of the variation in seed‐set and germination among the eight parent plants. Of these effects, 50 per cent were maternal and 50 per cent were paternal. There was no interaction between parental effects and offspring nuclear genotypes. These results suggest that, although parental effects do influence seed number and germination, parents do not differentially provision inbred and outbred offspring, and therefore differences in fitness between inbred and outbred offspring can be attributed to their nuclear genotypes.