Lm. Wolfe, INBREEDING DEPRESSION IN HYDROPHYLLUM-APPENDICULATUM - ROLE OF MATERNAL EFFECTS, CROWDING, AND PARENTAL MATING HISTORY, Evolution, 47(2), 1993, pp. 374-386
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.