INBREEDING DEPRESSION IN HYDROPHYLLUM-APPENDICULATUM - ROLE OF MATERNAL EFFECTS, CROWDING, AND PARENTAL MATING HISTORY

This paper examines several aspects of the expression of inbreeding de pression in an outcrossing, obligately biennial plant, Hydrophyllum ap pendiculatum (Hydrophyllaceae). The amount of inbreeding depression de tected was small during the first year of life but increased with age and had significant effects on adult size and reproductive traits. The lack of significant inbreeding depression during early growth is like ly due to the overriding influence of maternal environmental effects o n seed size and seedling growth. However, as maternal effects decrease d with age, the seedling's own genotype became a more important determ inant of its fate. To examine whether the expression of inbreeding dep ression was sensitive to ecological conditions, selfed and outcrossed seedlings were grown alone or with other H. appendiculatum seedlings. No inbreeding depression was detected in the plants grown alone. In co ntrast, under competitive conditions, outcrossed seedlings were signif icantly larger than selfed seedlings by the end of the first growing s eason. To address whether parental mating history influences the amoun t of inbreeding depression expressed, I examined the consequences of t wo successive generations of selfing on seed set and seed weight. The amount of inbreeding depression increased following the second generat ion of selfing. In the first generation, seed set and seed weight diff ered by less than 5% between selfed and outcrossed progeny. However, b oth traits were 15% greater for outcrossed plants after two generation s. These results indicate that the alleles responsible for the reducti ons in these traits were not purged and suggest the action of multiple loci with deleterious effects.