Pollination, mating system, and distribution of genetic variation within populations of Camellia japonica L. (Theaceae)

Aspects of the pollination biology, the mating system, and the distribution of genetic variation were investigated within natural populations of Camellia japonica in Japan. Field assessment of the outcrossing rate through pollination experiments indicated complete outcrossing. No significant inter-seasonal variation in the outcrossing rate was detected. Fruit set under natural conditions appears to be low, due to both lack of pollination and fruit abortion following fertilization.;Flower characteristics, the foraging behavior of insects and birds, the almost total lack of C. japonica pollen on insects, and the results of a bird exclusion experiment all support ornithophily as the mode of pollination. Nectar quantity and solute concentration are typical for passerine bird-pollinated flowers, but the high sucrose to hexose ratio and high amino acid content are atypical.;Quantitative estimates of the outcrossing rate were obtained by the electrophoretic analysis of seed progeny arrays from six populations. Multilocus outcrossing rate estimates (t;The distribution of genetic variation among spatial groups and size classes of trees was investigated in two populations. Heterogeneity chi-square analysis showed significant variation in allele frequencies between spatial groups, but little differentiation between size classes. F-statistic analysis showed a moderate degree of differentiation between spatial groups. There was no compelling evidence for selection for particular alleles, and little evidence for heterozygote advantage.;This study is significant as a detailed study of the distribution of genetic variation within natural populations of a bird-pollinated, outcrossing woody angiosperm. The results presented may also help in the design of strategies for sampling genetic variation within natural populations, and the elucidation of optimal strategies for the conservation of genetic resources.